Gait & Posture 41 (2015) 282–287
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Effects of focal ankle joint cooling on unipedal static balance in individuals with and without chronic ankle instability Kyung-Min Kim a,*, Joseph M. Hart b, Susan A. Saliba b, Jay Hertel b a b
Texas State University, San Marcos, TX, United States University of Virginia, Charlottesville, VA, United States
A R T I C L E I N F O
A B S T R A C T
Article history: Received 27 April 2014 Received in revised form 5 September 2014 Accepted 16 October 2014
Application of cryotherapy over an injured joint has been shown to improve muscle function, yet it is unknown how ankle cryotherapy affects postural control. Our purpose was to determine the effects of a 20-min focal ankle joint cooling on unipedal static stance in individuals with and without chronic ankle instability (CAI). Fifteen young subjects with CAI (9 males, 6 females) and 15 healthy gender-matched controls participated. All subjects underwent two intervention sessions on different days in which they had a 1.5 L plastic bag filled with either crushed ice (active treatment) or candy corn (sham) applied to the ankle. Unipedal stance with eyes closed for 10 s were assessed with a forceplate before and after each intervention. Center of pressure (COP) data were used to compute 10 specific dependent measures including velocity, area, standard deviation (SD), and percent range of COP excursions, and mean and SD of time-to-boundary (TTB) minima in the anterior–posterior (AP) and mediolateral directions. For each measure a three-way (Group–Intervention–Time) repeated ANOVAs found no significant interactions and main effects involving intervention (all Ps > 0.05). There were group main effects found for mean velocity (F(1,28) = 6.46, P = .017), area (F(1,28) = 12.83, P = .001), and mean of TTB minima in the AP direction (F(1,28) = 5.19, P = .031) indicating that the CAI group demonstrated greater postural instability compared to the healthy group. Postural control of unipedal stance was not significantly altered following focal ankle joint cooling in groups both with and without CAI. Ankle joint cryotherapy was neither beneficial nor harmful to single leg balance. ß 2014 Elsevier B.V. All rights reserved.
Keywords: Cryotherapy Postural control Center of pressure
1. Introduction Chronic ankle instability (CAI) is a debilitating collection of symptoms that persists following an initial ankle sprain [1,2]. It has been documented that approximately 30% of ankle sprain patients develop CAI [2]. CAI is primarily characterized by repetitive bouts of the ankle giving way, feeling of ankle instability, and recurrent ankle sprains [3]. Although CAI has been associated with a variety of mechanical and sensorimotor deficits [1,2], postural control impairments have been suggested as a primary contributing factor [4]. Rehabilitation programs with an emphasis on postural control for patients with CAI have been shown to lead to improved clinical outcomes [5].
* Corresponding author at: Department of Health and Human Performance, Texas State University, San Marcos, TX 78666, United States. Tel.: +1 512 245 4373; fax: +1 512 245 8678. E-mail address: [email protected] (K.-M. Kim). http://dx.doi.org/10.1016/j.gaitpost.2014.10.017 0966-6362/ß 2014 Elsevier B.V. All rights reserved.
Cryotherapy is one of the most common modalities used in sports medicine. Traditionally, it is used for a variety of treatment purposes including decreased inflammation, pain, swelling, and muscle spasm [6,7]. Application of cryotherapy over a joint using one or two ice bags has been shown to increase muscle activation [8–12] and potentially lead to muscle strength gains [10,12,13]. These studies [10,11] attributed the improved muscle function to increased alpha motoneuron recruitment following joint cooling. Recently, cryotherapy applied to the ankle joint has been found to facilitate alpha motoneuron pool excitability of the soleus and fibularis longus in individuals with CAI [8,9]. Furthermore, knee cryotherapy was found to restore deficits in quadriceps muscle fiber conduction velocity [13], and also negated the functional movement deficiencies associated with experimentally induced knee joint effusion [14]. These results suggested that joint cryotherapy might have therapeutic potential to enhance functional outcomes in patients with joint pathology. Ankle cryotherapy resulting in increased alpha motoneuron pool excitability (aMNPE) may have the potential to improve
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postural control. There are multiple studies determining that decreased aMNPE is associated with postural control deficits in individuals with postural instability due to various pathologies including CAI [15–17]. There is also evidence that an intervention, electrical perturbation during bipedal standing, directly aimed at evoking aMNPE did restore the diminished aMNPE, and lead to improvement in postural control [18]. There was a strong correlation between changes in aMNPE and postural control following the intervention [18]. These findings indicate that decreased aMNPE may play a role in postural control deficits. Two previous studies [19,20] have assessed unipedal postural control performance following ankle joint cooling, and both reported that balance was not adversely affected. However, these findings are not convincing because of methodological limitations including the lack of a control condition. This warrants a follow-up study with a sound design and more outcome variables of postural control to confirm or refute the previous findings. We were interested in how the ankle cryotherapy would affect not only normal postural control in healthy subjects, but also impaired postural control in subjects with CAI because focal ankle joint cooling has been demonstrated to increase aMNPE in both groups [8–10,21]. Therefore, the purpose of the present study was to determine the effects of a 20-min focal ankle joint cooling on quiet unipedal postural control in individuals with and without CAI. We hypothesized that the ankle cryotherapy would significantly improve static postural control in individuals with and without CAI. 2. Methods We performed a laboratory study that employed a crossover design. Independent variables were group (CAI and healthy control), intervention (ankle cryotherapy, sham), and time (preand post-intervention). Primary dependent variables were 10 parameters of center of pressure (COP) excursions recorded during a quiet unipedal stance for 10 s. Secondary outcomes were scores on a visual analog scale to represent subject’s perceived level of postural control during the 10-s unipedal stance and the number of failed trials of the unipedal task. All subjects received the ankle cryotherapy and sham treatments on separate days at least 24 h apart. The order of treatment sessions was randomly assigned. All outcomes were collected before and immediately following intervention. 2.1. Subjects Fifteen subjects with CAI and 15 healthy controls without any history of ankle sprains recruited from a university community participated in the present study. Subject demographics are shown in Table 1. Subjects were assigned to either the CAI group or healthy control group based upon their current ankle status and a history of ankle injury. We utilized the previously reported Table 1 Subject demographics (mean and standard deviation). Group
CAI
Subjects Sex Age (yrs) Height (cm) Mass (kg) FAAM-ADL (%) FAAM-Sport (%) Number of previous ankle sprains Months since the latest ankle sprain
15 15 6 females, 9 males 6 females, 9 males 22.6 5.8 23.8 5.8 174.7 8.1 171.9 9.9 74.9 12.8 68.9 15.5 82.7 6.5 100 65.0 9.3 99.7 1.3 4.9 4.8 0 13.5 7.3 N/A
Healthy control
Abbreviation: CAI, chronic ankle instability; FAAM, foot and ankle ability measure; ADL, activity of daily living.
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inclusion criteria for each group [22,23]. Subjects were excluded if they reported current lower extremity injuries within the past 6 weeks, any history of lower extremity surgery, neuropathies, diabetes, balance disorder, Raynaud’s diseases, and any cold induced circulatory problems, and other conditions known to affect balance. For subjects with bilateral CAI, their self-reported worst limb was used, and limbs of healthy controls were sidematched to CAI subjects for analysis purposes. All subjects provided informed consent and the study was approved by the University’s Institutional Review Board. 2.2. Instruments Postural control during unipedal stance was assessed with the Accusway Plus forceplate (AMTI, Watertown, MA). COP was calculated from the three dimensional forces and moments arising from the foot/forceplate interface through the Balance Clinic Software (AMTI, Watertown, MA). COP data were sampled at a rate of 50 Hz and a fourth-order low zero lag, low-pass filter with a cutoff frequency of 5 Hz was used to filter the COP data [24,25]. A custom software program processed in MatLab (MathWorks, Inc., Natick, MA) and the Balance Clinic were used to calculate 10 specific COP parameters [24,25]. Skin surface and ambient air temperatures were collected using PT-6 surface thermocouples (Physitemp Instruments Inc, Clifton, NJ) interfaced to Physitemp Thermes USB electrothermometer (Physitemp Instruments, Inc., Clifton, NJ). The temperature data were stored through the MCC DAQ Software (Measurement ComputingTM, Norton, MA). 2.3. Procedures 2.3.1. Postural control in Unipedal stance Subjects performed three trials of unipedal stance with eyes closed for 10 s on a forceplate. Subjects were instructed to perform a unipedal stance on the involved limbs of subjects with CAI or the side-matched limbs of healthy controls. Specific foot positions on the forceplate and balance assessment were consistent with a previously reported manner [25]. 2.3.2. Ankle cryotherapy and sham treatments Subjects were positioned supine on a table to receive either ankle cryotherapy or sham treatments on different days at least 24 h apart. The ankle cryotherapy consisted of one plastic bag filled with 1.5 L of crushed ice that was applied to the anterior aspect of the ankle with an elastic bandage to secure it for 20 min. The sham treatment consisted of the same size bag, but filled with the same volume of room temperature candy corn that was placed on the same location of the ankle with an elastic bandage for 20 min. All participants were asked to avoid any forms of cryotherapy treatments at least 24 h prior to study participation. 2.3.3. Surface temperature Two surface thermocouples were used to measure skin surface temperatures at two sites: one over the sinus tarsi of the ankle and the other over the soleus muscle belly 2–3 cm distal to the gastrocnemius. Another surface thermocouple measured ambient air temperature in the laboratory. Three measurements at each site were collected before and immediately after removing an ice bag from the ankle joint. These temperature measurements were recorded to ensure that the ankle cryotherapy cooled only the ankle joint, not the surrounding muscles. 2.3.4. Visual analog scale Visual analog scales [22,26] were used to quantify a perceived level of balance performance during unipedal stance. After each
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trial of the postural task, subjects were rated the level of their balance performance by drawing a vertical line across a 100 mm horizontal line ranging from 0 to100 with 0 representing ‘‘worst balance’’ and 100 indicating ‘‘best balance’’.
measurements between pre- and post-intervention. Alpha level was set a priori at p 0.05. All statistical analyses were performed using SPSS 19.0 statistical software (SPSS Incorporated, Chicago, IL, USA).
2.4. Data processing
3. Results
Postural control of unipedal stance was assessed with 10 specific COP measures. There were 6 traditional COP measures and 4 time-to-boundary (TTB) measures utilized. The traditional COP measures included the mean velocity, area, standard deviation, and percent of available range used for COP excursions. For all of these measures, a larger value indicates greater postural instability. In addition to the traditional measures, TTB measures were calculated to provide insight into the spatiotemporal aspects of postural control as these measures have been shown to be sensitive to detecting balance deficits associated with CAI [25,27]. The methods used to compute TTB measures in the anteroposterior (AP) and mediolateral [28] directions have been previously described in detail [24,25,27]. Specific TTB measures serving as dependent variables were mean of the minima and the standard deviation of the minima in the AP and ML directions. A lower TTB measure indicates greater postural instability [24,25,27]. 2.5. Statistical analysis The mean of each outcome measure was used for statistical analysis. For each COP measure, a three-way ANOVA (Group, Intervention, and Time) with repeated measures were performed to determine the effects of ankle cryotherapy on postural control. Another three-way ANOVA was conducted for VAS scores to assess subjective intervention effects on balance performance during unipedal stance. Post hoc simple contrasts were conducted to identify specific differences in the presence of significant interactions or main effects. Consistent with contemporary statistical recommendations [29], we elected to not apply corrections to the level of significance for multiple comparisons. The number of failed trials was analyzed with nonparametic statistical tests because the data were not found normally distributed. Mann–Whitney U tests were used to determine group difference at each of measurement points: pre-and post-intervention (ankle cryotherapy and sham). Additionally, Wilcoxon Signed Rank tests were utilized to assess whether pre-intervention numbers of failed trials were different from post-intervention. For the control variable of temperature, dependent t tests were performed for differences in temperature
Descriptive statistics for all measures are presented in Tables 2–5. There were no significant interactions (all Ps > 0.05) found for any of the COP measures, however, there were significant group main effects found in the mean COP velocity (F(1,28) = 6.46, P = .017), COP area (F(1,28) = 12.83, P = .001), and mean of TTB minima in the AP direction (F(1,28) = 5.19, P = .031). The CAI group was found to sway significantly faster (8.3 0.41 cm/s) and over a larger area (25.2 1.2 cm2) than the healthy control group (6.8 0.41 cm/s, 18.5 1.3 cm2). The mean of TTB minima in the AP direction was significantly lower in the CAI group (4.7 0.36 s) than in the healthy group (5.9 0.36 s). Additionally, there was a significant time main effect for mean COP velocity (F(1,28) = 4.83, P = .036) with baseline measures (7.7 0.33 cm/s) being significantly greater than follow-up measures (7.4 0.27 cm/s). Significant interactions were not found on the VAS scores for subjective balance performance, however, a group main effect (F(1,28) = 5.05, P = .033) was observed. The CAI group (44.1 4.0 mm) reported worse perceptions of postural stability than the control group (56.9 4.0 mm). The CAI group also had more failed trials than the healthy group at all measurement points (all Ps < .029). Neither group significantly changed the number of failed trials following either ankle cryotherapy or sham (Table 4). Our cooling method using an ice bag applied to the ankle joint significantly decreased the skin surfaces overlying the ankle in both CAI (t(14) = 17.30, P < .001) and healthy groups (t(14) = 18.23, P < .001), but no significant changes in soleus surface temperature were noted. As expected, our sham treatment using candy corn did not change skin surface temperature at either location. The ambient room temperatures remained unchanged before and after intervention (Table 5).
4. Discussion Our hypothesis that ankle joint focal cooling would improve postural control during unipedal stance in groups with and without CAI was rejected as the ankle cryotherapy did not significantly affect any of the postural control measures in either group. The findings were consistent with an absence of changes found in VAS scores and the number of failed trials following cryotherapy. The CAI group did demonstrate worse postural control than the control group regardless of the administration of cryotherapy. These results clearly showed that the individuals with CAI had postural control deficits compared to the healthy controls, which agrees with the conclusions recently made in multiple systematic reviews [30–32]. Our method to cool the ankle joint with an ice bag was found to significantly decrease the skin surface temperatures at ankle joint, but not the soleus muscles, indicating the hypothermal effect was given only to the ankle joint. Our results clearly showed ankle joint cryotherapy did not negatively affect postural control. To our knowledge, only two
Table 2 Center of pressure (COP) measures taken during unipedal stance for 10 s (mean and standard deviation). COP parameters
Chronic ankle instability Ankle cryotherapy
Velocity (cm/s)a,b SD ML SD AP Area (cm2)a Percent range ML (%) Percent range AP (%) Mean Min. TTBML(s) Mean Min. TTBAP(s)a SD Min. TTBML SD Min. TTBAP
Healthy control Ankle cryotherapy
Sham
Baseline
Follow-up
Sham Baseline
Follow-up
Baseline
Follow-up
Baseline
Follow-up
8.55 2.5 0.53 0.26 0.71 0.40 26.3 9.7 22.6 11.5 13.7 7.9 1.98 0.92 4.66 1.66 1.70 0.91 3.04 1.52
7.75 1.7 0.50 0.25 0.65 0.31 23.6 7.5 21.5 10.3 12.6 7.7 2.02 0.95 4.80 1.51 1.80 1.07 3.32 1.55
8.47 2.1 0.54 0.28 0.66 0.31 24.8 5.1 22.3 10.5 13.1 6.6 1.89 0.75 4.63 1.77 1.71 0.72 3.20 1.54
8.36 1.8 0.54 0.28 0.70 0.36 26.1 6.1 22.4 11.3 13.6 7.2 2.00 0.89 4.74 1.62 1.81 1.01 3.23 1.31
6.93 1.3 0.51 0.27 0.59 0.28 19.0 4.6 22.8 12.6 11.3 5.9 2.15 1.24 5.86 1.35 1.90 0.50 3.86 1.81
6.73 1.5 0.50 0.25 0.57 0.29 18.3 6.3 23.1 11.3 10.4 5.6 1.99 0.94 5.92 1.47 1.85 0.46 3.93 1.50
6.88 1.6 0.51 0.30 0.64 0.39 18.7 7.5 23.1 13.1 12.3 8.3 2.02 1.04 5.78 1.39 1.92 0.59 3.92 1.47
6.65 1.3 0.52 0.27 0.61 0.37 17.8 4.6 23.5 12.3 10.6 5.7 2.08 0.94 5.98 1.27 2.13 0.51 4.52 1.74
Abbreviation: SD, standard deviation; ML, mediolateral; AP, anteroposterior; TTB, time-to-boundary; Min, minima. a A group main effect indicates that the CAI group had postural control deficits compared to the healthy control group. b A time main effect indicates that postural control improved over time.
K.-M. Kim et al. / Gait & Posture 41 (2015) 282–287 Table 3 Visual analog scale scores (mm) of subjective levels of postural control during unipedal stance for 10 s (mean and standard deviation). Ankle cryotherapy
Sham
Baseline
Baseline
Follow-up
Follow-up
Chronic ankle instabilitya 42.3 18.1 44.27 15.8 45.80 17.5 44.00 13.3 Healthy control 54.3 18.2 58.40 19.8 58.47 19.28 56.33 20.9 a A group main effect indicates that the CAI group perceived less levels of balance performance than the healthy control group.
Table 4 Numbers of failed trials of a 10-s unipedal stance (median and range). It is noted that there were no differences before and after intervention. Ankle cryotherapy
Chronic ankle instability Healthy control
Sham
Baseline
Follow-up
Baseline
Follow-up
2 (0–8)a 0 (0–2)
2 (0–6) 0 (0–2)
1 (0–8)a 0 (0–3)
1 (0–7)a 0 (0–2)
a A group difference indicates that the CAI group failed more numbers of trials than the healthy control group.
studies previously assessed unipedal postural control following ankle joint cooling in healthy subjects [19,20]. They both reported that postural control in healthy subjects was not substantially affected after cryotherapy. Although the methodology of the two previous studies may be criticized, combined with the results of our current study with a more robust design and additional postural control measures, there appears to be mounting evidence indicating the ankle cryotherapy does not adversely affect postural control. One previous study [33] has examined the effects of cryotherapy on single leg balance in patients with lateral ankle sprains within the 4–7 days. The balance performance, as assessed by ML postural sway variability, was impaired following lower-leg immersion cryotherapy in which the injured ankle was immersed for 20 min in a tub containing an ice water mixture [33]. This result conflicts with our findings of no influence of ankle joint cooling on postural control in patients with CAI. This discrepancy may be due to the difference in body area being cooled (lower limb immersion versus focal cooling of the ankle joint) or the nature of the joint pathology (acute versus chronic) [33]. We attempted to locally cool the skin surface overlying the ankle joint with an ice bag because of previously reported favorable outcomes on muscle activation following cold application with an ice bag to a joint [8–14]. Our joint cooling technique significantly decreased only the joint surface, but not the soleus muscle surrounding the joint. In contrast, the immersion cooling technique used in the previous study likely cooled all structures in the lower leg including the entire foot, ankle, and extrinsic muscles and tendons in the lower leg. The immersion cryotherapy likely decreased sensitivity of cutaneous, articular, and musculotendinous receptors thus
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resulting in alterations in single leg balance [33–35]. Postural control impairments following the ice water immersion have also been found in healthy participants [36]. However, focal ankle joint cooling has not resulted in postural control deficits in healthy participants [19,20]. These results suggest that ice water immersion that cools both joints and their surrounding muscles may have different effects than focal joint cooling. We surmise that postural control in unipedal stance may be impaired following cooling the lower leg due to direct muscle cooling, but not after focally cooling the ankle joint. It is believed that the multiple sensory inputs from afferent structures in the ankle joint are necessary for the central nervous system (CNS) to execute successful postural control, and alterations in these sensory activities may cause alterations in postural control [2,25]. Three categories of mechanoreceptors responsible for sensing postural information to CNS in the ankle joint includes cutaneous, articular, and musculotendious receptors. It is reasonable to assume that both focal ankle joint cooling and ice water immersion would affect cutaneous, articular, and tendonous receptors on the anterolateral aspect of the ankle. The ice water immersion would also influence articular receptors elsewhere around the ankle and foot, but probably more importantly, it would also cool the muscle spindles in the intrinsic and extrinsic foot muscles. Muscles spindles, especially in the triceps surae, are extremely important in regulating postural control [34,35,37]. The study utilizing mechanical vibration applied to the triceps surae as a perturbing tool demonstrated considerable postural deviations, indicating a vital role of muscle spindles in contributing to proprioception that is essential for accurate postural control [38,39]. Thus, the differing results on postural control between focal ankle joint cooling and ice water immersion are likely due to the influence that postural control has on the muscle spindles. In addition to potential sensory effects of ankle joint cooling, there is evidence that ice bags applied to the knee or ankle joint significantly enhance motor function including muscle activation [8–13], muscle fiber nerve conduction velocity [13], force output [10,12,13], and functional performance [14]. It has been suggested that these improvements are due to increased motoneuron recruitment following joint cooling [10,11]. We hypothesized that ankle joint cryotherapy would enhance postural control in individuals both with and without CAI because the CNS would better accommodate to postural demands with the expanded alpha motoneuron pool of the ankle stabilizing muscles. However, our results did not support this hypothesis. One likely explanation for these results may be the absence of changes in motoneuron pool excitability (MNPE) of ankle muscles after the similar ice treatment while standing [40]. Recently, Kim et al. [40] assessed MNPE of the soleus and fibularis longus, as assessed by Hoffmann reflex while their subjects laid prone and then stood in bipedal and unipedal stances. They found a 20-min ice bag application to the ankle joint significantly increased MNPE in both muscles while prone in a manner consistent with previous investigations [8,9], but they did not find any changes in MNPE in either standing
Table 5 Skin surface temperatures (8C, mean and standard deviation). Group
Site
Ankle cryotherapy Baseline
Sham Follow-up
Baseline
Follow-up
a
Chronic ankle instability
Ankle Soleus Room
30.86 2.1 31.47 1.9 23.64 1.6
12.08 2.8 31.90 1.5 23.86 1.5
30.23 2.1 31.03 1.9 23.21 2.1
30.68 1.7 31.19 1.8 23.69 2.2
Healthy control
Ankle Soleus Room
30.49 1.7 30.92 1.9 22.95 1.8
12.21 2.7a 30.74 1.8 22.89 1.3
30.16 1.5 30.78 1.4 22.86 1.2
30.25 1.7 30.83 1.2 22.93 1.2
a
A difference indicates that ankle cryotherapy significantly decreased the skin surface overlying the ankle joint.
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postures after cryotherapy. These results indicate that the increased MNPE associated with ankle joint cooling found in a non-weight bearing position may not translate to weight bearing positions. This discrepancy may have important applications for the use of cryotherapy as a disinhibitory modality prior to therapeutic exercise. In addition to the neurophysiological explanations of our results, our methodological choices may have influenced our results. First, we used a 20-min ice bag application to the ankle joint while some authors [8–10] found improved muscle function with 30-min of cold application. However, it should be noted that 20-min of ice treatment has been shown to elicit MNPE of the soleus and fibularis longus in both individuals with and without CAI [40]. Secondly, it has been suggested that exercise intervention following an ice bag application to a joint would facilitate muscle function [10–12], but the present study did not include an exercise protocol because it focused on isolated effects of joint cooling on postural control. Finally, the present study did not utilize a true control condition (no intervention), but had two treatment conditions of cryotherapy and sham. In both conditions the bag containing either ice or candy corn was secured to the ankle with an elastic bandage. It is possible that joint compression with an elastic bandage may affect single leg balance performance, however, it must be noted that the compression wrap was removed when the treatment time elapsed and all balance testing was performed without compression. The results of the current study may be important in clinical settings where there is an impression of potential detrimental effects of cryotherapy on muscle function. We agree that direct muscle cooling may impair postural control [33,36], however, our results showed that focal cooling of the ankle joint did not impair postural control. It does not appear that cryotherapy to either the ankle joint or its surrounding musculature can enhance unipedal postural control. On the other hand, focal joint cooling may be safe to use prior to therapeutic exercises aimed at improving muscle activation and strength [10–13]. When cryotherapy is necessary in the beginning of a rehabilitation session, it is important to focus on ankle joint cooling to avoid deleterious effects on postural balance associated with more global cooling procedures including the surrounding muscles as would occur with cold water immersion. Surprisingly, we found an improvement in postural control regardless of which intervention was applied, as there was a significant decrease in the mean COP velocity after interventions. This result may reflect a learning effect and indicate the COP velocity measure may be more sensitive to change than other COP measures, requiring a practice trial. It is also possible to speculate that joint compression provided by elastic bandage used to secure a plastic bag of ice or candy corn (sham) plays a role in slowing the COP excursions. However, it is noted that the ankle joint was released from the compression during postural control assessments. In conclusion, we found that postural control during unipedal stance was impaired among individuals with CAI, but postural control was not altered following a 20-min focal ankle joint cooling in individuals both with and without CAI. These findings indicate that a single session of ankle joint cryotherapy is neither beneficial nor harmful for single leg balance performance. Acknowledgements National Athletic Trainers’ Association Research and Education Foundation funded the present study through Doctoral Grant Program. The study sponsor does not play any role in the study design, in the collection, analysis and interpretation of data, in the writing of the manuscript, and in the decision to submit the manuscript for publication.
Conflict of interest statement: There is no conflict of interests for any of the authors.
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Effects of focal ankle joint cooling on unipedal static balance in individuals with and without chronic ankle instability Kyung-Min Kim a,*, Joseph M. Hart b, Susan A. Saliba b, Jay Hertel b a b
Texas State University, San Marcos, TX, United States University of Virginia, Charlottesville, VA, United States
A R T I C L E I N F O
A B S T R A C T
Article history: Received 27 April 2014 Received in revised form 5 September 2014 Accepted 16 October 2014
Application of cryotherapy over an injured joint has been shown to improve muscle function, yet it is unknown how ankle cryotherapy affects postural control. Our purpose was to determine the effects of a 20-min focal ankle joint cooling on unipedal static stance in individuals with and without chronic ankle instability (CAI). Fifteen young subjects with CAI (9 males, 6 females) and 15 healthy gender-matched controls participated. All subjects underwent two intervention sessions on different days in which they had a 1.5 L plastic bag filled with either crushed ice (active treatment) or candy corn (sham) applied to the ankle. Unipedal stance with eyes closed for 10 s were assessed with a forceplate before and after each intervention. Center of pressure (COP) data were used to compute 10 specific dependent measures including velocity, area, standard deviation (SD), and percent range of COP excursions, and mean and SD of time-to-boundary (TTB) minima in the anterior–posterior (AP) and mediolateral directions. For each measure a three-way (Group–Intervention–Time) repeated ANOVAs found no significant interactions and main effects involving intervention (all Ps > 0.05). There were group main effects found for mean velocity (F(1,28) = 6.46, P = .017), area (F(1,28) = 12.83, P = .001), and mean of TTB minima in the AP direction (F(1,28) = 5.19, P = .031) indicating that the CAI group demonstrated greater postural instability compared to the healthy group. Postural control of unipedal stance was not significantly altered following focal ankle joint cooling in groups both with and without CAI. Ankle joint cryotherapy was neither beneficial nor harmful to single leg balance. ß 2014 Elsevier B.V. All rights reserved.
Keywords: Cryotherapy Postural control Center of pressure
1. Introduction Chronic ankle instability (CAI) is a debilitating collection of symptoms that persists following an initial ankle sprain [1,2]. It has been documented that approximately 30% of ankle sprain patients develop CAI [2]. CAI is primarily characterized by repetitive bouts of the ankle giving way, feeling of ankle instability, and recurrent ankle sprains [3]. Although CAI has been associated with a variety of mechanical and sensorimotor deficits [1,2], postural control impairments have been suggested as a primary contributing factor [4]. Rehabilitation programs with an emphasis on postural control for patients with CAI have been shown to lead to improved clinical outcomes [5].
* Corresponding author at: Department of Health and Human Performance, Texas State University, San Marcos, TX 78666, United States. Tel.: +1 512 245 4373; fax: +1 512 245 8678. E-mail address: [email protected] (K.-M. Kim). http://dx.doi.org/10.1016/j.gaitpost.2014.10.017 0966-6362/ß 2014 Elsevier B.V. All rights reserved.
Cryotherapy is one of the most common modalities used in sports medicine. Traditionally, it is used for a variety of treatment purposes including decreased inflammation, pain, swelling, and muscle spasm [6,7]. Application of cryotherapy over a joint using one or two ice bags has been shown to increase muscle activation [8–12] and potentially lead to muscle strength gains [10,12,13]. These studies [10,11] attributed the improved muscle function to increased alpha motoneuron recruitment following joint cooling. Recently, cryotherapy applied to the ankle joint has been found to facilitate alpha motoneuron pool excitability of the soleus and fibularis longus in individuals with CAI [8,9]. Furthermore, knee cryotherapy was found to restore deficits in quadriceps muscle fiber conduction velocity [13], and also negated the functional movement deficiencies associated with experimentally induced knee joint effusion [14]. These results suggested that joint cryotherapy might have therapeutic potential to enhance functional outcomes in patients with joint pathology. Ankle cryotherapy resulting in increased alpha motoneuron pool excitability (aMNPE) may have the potential to improve
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postural control. There are multiple studies determining that decreased aMNPE is associated with postural control deficits in individuals with postural instability due to various pathologies including CAI [15–17]. There is also evidence that an intervention, electrical perturbation during bipedal standing, directly aimed at evoking aMNPE did restore the diminished aMNPE, and lead to improvement in postural control [18]. There was a strong correlation between changes in aMNPE and postural control following the intervention [18]. These findings indicate that decreased aMNPE may play a role in postural control deficits. Two previous studies [19,20] have assessed unipedal postural control performance following ankle joint cooling, and both reported that balance was not adversely affected. However, these findings are not convincing because of methodological limitations including the lack of a control condition. This warrants a follow-up study with a sound design and more outcome variables of postural control to confirm or refute the previous findings. We were interested in how the ankle cryotherapy would affect not only normal postural control in healthy subjects, but also impaired postural control in subjects with CAI because focal ankle joint cooling has been demonstrated to increase aMNPE in both groups [8–10,21]. Therefore, the purpose of the present study was to determine the effects of a 20-min focal ankle joint cooling on quiet unipedal postural control in individuals with and without CAI. We hypothesized that the ankle cryotherapy would significantly improve static postural control in individuals with and without CAI. 2. Methods We performed a laboratory study that employed a crossover design. Independent variables were group (CAI and healthy control), intervention (ankle cryotherapy, sham), and time (preand post-intervention). Primary dependent variables were 10 parameters of center of pressure (COP) excursions recorded during a quiet unipedal stance for 10 s. Secondary outcomes were scores on a visual analog scale to represent subject’s perceived level of postural control during the 10-s unipedal stance and the number of failed trials of the unipedal task. All subjects received the ankle cryotherapy and sham treatments on separate days at least 24 h apart. The order of treatment sessions was randomly assigned. All outcomes were collected before and immediately following intervention. 2.1. Subjects Fifteen subjects with CAI and 15 healthy controls without any history of ankle sprains recruited from a university community participated in the present study. Subject demographics are shown in Table 1. Subjects were assigned to either the CAI group or healthy control group based upon their current ankle status and a history of ankle injury. We utilized the previously reported Table 1 Subject demographics (mean and standard deviation). Group
CAI
Subjects Sex Age (yrs) Height (cm) Mass (kg) FAAM-ADL (%) FAAM-Sport (%) Number of previous ankle sprains Months since the latest ankle sprain
15 15 6 females, 9 males 6 females, 9 males 22.6 5.8 23.8 5.8 174.7 8.1 171.9 9.9 74.9 12.8 68.9 15.5 82.7 6.5 100 65.0 9.3 99.7 1.3 4.9 4.8 0 13.5 7.3 N/A
Healthy control
Abbreviation: CAI, chronic ankle instability; FAAM, foot and ankle ability measure; ADL, activity of daily living.
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inclusion criteria for each group [22,23]. Subjects were excluded if they reported current lower extremity injuries within the past 6 weeks, any history of lower extremity surgery, neuropathies, diabetes, balance disorder, Raynaud’s diseases, and any cold induced circulatory problems, and other conditions known to affect balance. For subjects with bilateral CAI, their self-reported worst limb was used, and limbs of healthy controls were sidematched to CAI subjects for analysis purposes. All subjects provided informed consent and the study was approved by the University’s Institutional Review Board. 2.2. Instruments Postural control during unipedal stance was assessed with the Accusway Plus forceplate (AMTI, Watertown, MA). COP was calculated from the three dimensional forces and moments arising from the foot/forceplate interface through the Balance Clinic Software (AMTI, Watertown, MA). COP data were sampled at a rate of 50 Hz and a fourth-order low zero lag, low-pass filter with a cutoff frequency of 5 Hz was used to filter the COP data [24,25]. A custom software program processed in MatLab (MathWorks, Inc., Natick, MA) and the Balance Clinic were used to calculate 10 specific COP parameters [24,25]. Skin surface and ambient air temperatures were collected using PT-6 surface thermocouples (Physitemp Instruments Inc, Clifton, NJ) interfaced to Physitemp Thermes USB electrothermometer (Physitemp Instruments, Inc., Clifton, NJ). The temperature data were stored through the MCC DAQ Software (Measurement ComputingTM, Norton, MA). 2.3. Procedures 2.3.1. Postural control in Unipedal stance Subjects performed three trials of unipedal stance with eyes closed for 10 s on a forceplate. Subjects were instructed to perform a unipedal stance on the involved limbs of subjects with CAI or the side-matched limbs of healthy controls. Specific foot positions on the forceplate and balance assessment were consistent with a previously reported manner [25]. 2.3.2. Ankle cryotherapy and sham treatments Subjects were positioned supine on a table to receive either ankle cryotherapy or sham treatments on different days at least 24 h apart. The ankle cryotherapy consisted of one plastic bag filled with 1.5 L of crushed ice that was applied to the anterior aspect of the ankle with an elastic bandage to secure it for 20 min. The sham treatment consisted of the same size bag, but filled with the same volume of room temperature candy corn that was placed on the same location of the ankle with an elastic bandage for 20 min. All participants were asked to avoid any forms of cryotherapy treatments at least 24 h prior to study participation. 2.3.3. Surface temperature Two surface thermocouples were used to measure skin surface temperatures at two sites: one over the sinus tarsi of the ankle and the other over the soleus muscle belly 2–3 cm distal to the gastrocnemius. Another surface thermocouple measured ambient air temperature in the laboratory. Three measurements at each site were collected before and immediately after removing an ice bag from the ankle joint. These temperature measurements were recorded to ensure that the ankle cryotherapy cooled only the ankle joint, not the surrounding muscles. 2.3.4. Visual analog scale Visual analog scales [22,26] were used to quantify a perceived level of balance performance during unipedal stance. After each
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trial of the postural task, subjects were rated the level of their balance performance by drawing a vertical line across a 100 mm horizontal line ranging from 0 to100 with 0 representing ‘‘worst balance’’ and 100 indicating ‘‘best balance’’.
measurements between pre- and post-intervention. Alpha level was set a priori at p 0.05. All statistical analyses were performed using SPSS 19.0 statistical software (SPSS Incorporated, Chicago, IL, USA).
2.4. Data processing
3. Results
Postural control of unipedal stance was assessed with 10 specific COP measures. There were 6 traditional COP measures and 4 time-to-boundary (TTB) measures utilized. The traditional COP measures included the mean velocity, area, standard deviation, and percent of available range used for COP excursions. For all of these measures, a larger value indicates greater postural instability. In addition to the traditional measures, TTB measures were calculated to provide insight into the spatiotemporal aspects of postural control as these measures have been shown to be sensitive to detecting balance deficits associated with CAI [25,27]. The methods used to compute TTB measures in the anteroposterior (AP) and mediolateral [28] directions have been previously described in detail [24,25,27]. Specific TTB measures serving as dependent variables were mean of the minima and the standard deviation of the minima in the AP and ML directions. A lower TTB measure indicates greater postural instability [24,25,27]. 2.5. Statistical analysis The mean of each outcome measure was used for statistical analysis. For each COP measure, a three-way ANOVA (Group, Intervention, and Time) with repeated measures were performed to determine the effects of ankle cryotherapy on postural control. Another three-way ANOVA was conducted for VAS scores to assess subjective intervention effects on balance performance during unipedal stance. Post hoc simple contrasts were conducted to identify specific differences in the presence of significant interactions or main effects. Consistent with contemporary statistical recommendations [29], we elected to not apply corrections to the level of significance for multiple comparisons. The number of failed trials was analyzed with nonparametic statistical tests because the data were not found normally distributed. Mann–Whitney U tests were used to determine group difference at each of measurement points: pre-and post-intervention (ankle cryotherapy and sham). Additionally, Wilcoxon Signed Rank tests were utilized to assess whether pre-intervention numbers of failed trials were different from post-intervention. For the control variable of temperature, dependent t tests were performed for differences in temperature
Descriptive statistics for all measures are presented in Tables 2–5. There were no significant interactions (all Ps > 0.05) found for any of the COP measures, however, there were significant group main effects found in the mean COP velocity (F(1,28) = 6.46, P = .017), COP area (F(1,28) = 12.83, P = .001), and mean of TTB minima in the AP direction (F(1,28) = 5.19, P = .031). The CAI group was found to sway significantly faster (8.3 0.41 cm/s) and over a larger area (25.2 1.2 cm2) than the healthy control group (6.8 0.41 cm/s, 18.5 1.3 cm2). The mean of TTB minima in the AP direction was significantly lower in the CAI group (4.7 0.36 s) than in the healthy group (5.9 0.36 s). Additionally, there was a significant time main effect for mean COP velocity (F(1,28) = 4.83, P = .036) with baseline measures (7.7 0.33 cm/s) being significantly greater than follow-up measures (7.4 0.27 cm/s). Significant interactions were not found on the VAS scores for subjective balance performance, however, a group main effect (F(1,28) = 5.05, P = .033) was observed. The CAI group (44.1 4.0 mm) reported worse perceptions of postural stability than the control group (56.9 4.0 mm). The CAI group also had more failed trials than the healthy group at all measurement points (all Ps < .029). Neither group significantly changed the number of failed trials following either ankle cryotherapy or sham (Table 4). Our cooling method using an ice bag applied to the ankle joint significantly decreased the skin surfaces overlying the ankle in both CAI (t(14) = 17.30, P < .001) and healthy groups (t(14) = 18.23, P < .001), but no significant changes in soleus surface temperature were noted. As expected, our sham treatment using candy corn did not change skin surface temperature at either location. The ambient room temperatures remained unchanged before and after intervention (Table 5).
4. Discussion Our hypothesis that ankle joint focal cooling would improve postural control during unipedal stance in groups with and without CAI was rejected as the ankle cryotherapy did not significantly affect any of the postural control measures in either group. The findings were consistent with an absence of changes found in VAS scores and the number of failed trials following cryotherapy. The CAI group did demonstrate worse postural control than the control group regardless of the administration of cryotherapy. These results clearly showed that the individuals with CAI had postural control deficits compared to the healthy controls, which agrees with the conclusions recently made in multiple systematic reviews [30–32]. Our method to cool the ankle joint with an ice bag was found to significantly decrease the skin surface temperatures at ankle joint, but not the soleus muscles, indicating the hypothermal effect was given only to the ankle joint. Our results clearly showed ankle joint cryotherapy did not negatively affect postural control. To our knowledge, only two
Table 2 Center of pressure (COP) measures taken during unipedal stance for 10 s (mean and standard deviation). COP parameters
Chronic ankle instability Ankle cryotherapy
Velocity (cm/s)a,b SD ML SD AP Area (cm2)a Percent range ML (%) Percent range AP (%) Mean Min. TTBML(s) Mean Min. TTBAP(s)a SD Min. TTBML SD Min. TTBAP
Healthy control Ankle cryotherapy
Sham
Baseline
Follow-up
Sham Baseline
Follow-up
Baseline
Follow-up
Baseline
Follow-up
8.55 2.5 0.53 0.26 0.71 0.40 26.3 9.7 22.6 11.5 13.7 7.9 1.98 0.92 4.66 1.66 1.70 0.91 3.04 1.52
7.75 1.7 0.50 0.25 0.65 0.31 23.6 7.5 21.5 10.3 12.6 7.7 2.02 0.95 4.80 1.51 1.80 1.07 3.32 1.55
8.47 2.1 0.54 0.28 0.66 0.31 24.8 5.1 22.3 10.5 13.1 6.6 1.89 0.75 4.63 1.77 1.71 0.72 3.20 1.54
8.36 1.8 0.54 0.28 0.70 0.36 26.1 6.1 22.4 11.3 13.6 7.2 2.00 0.89 4.74 1.62 1.81 1.01 3.23 1.31
6.93 1.3 0.51 0.27 0.59 0.28 19.0 4.6 22.8 12.6 11.3 5.9 2.15 1.24 5.86 1.35 1.90 0.50 3.86 1.81
6.73 1.5 0.50 0.25 0.57 0.29 18.3 6.3 23.1 11.3 10.4 5.6 1.99 0.94 5.92 1.47 1.85 0.46 3.93 1.50
6.88 1.6 0.51 0.30 0.64 0.39 18.7 7.5 23.1 13.1 12.3 8.3 2.02 1.04 5.78 1.39 1.92 0.59 3.92 1.47
6.65 1.3 0.52 0.27 0.61 0.37 17.8 4.6 23.5 12.3 10.6 5.7 2.08 0.94 5.98 1.27 2.13 0.51 4.52 1.74
Abbreviation: SD, standard deviation; ML, mediolateral; AP, anteroposterior; TTB, time-to-boundary; Min, minima. a A group main effect indicates that the CAI group had postural control deficits compared to the healthy control group. b A time main effect indicates that postural control improved over time.
K.-M. Kim et al. / Gait & Posture 41 (2015) 282–287 Table 3 Visual analog scale scores (mm) of subjective levels of postural control during unipedal stance for 10 s (mean and standard deviation). Ankle cryotherapy
Sham
Baseline
Baseline
Follow-up
Follow-up
Chronic ankle instabilitya 42.3 18.1 44.27 15.8 45.80 17.5 44.00 13.3 Healthy control 54.3 18.2 58.40 19.8 58.47 19.28 56.33 20.9 a A group main effect indicates that the CAI group perceived less levels of balance performance than the healthy control group.
Table 4 Numbers of failed trials of a 10-s unipedal stance (median and range). It is noted that there were no differences before and after intervention. Ankle cryotherapy
Chronic ankle instability Healthy control
Sham
Baseline
Follow-up
Baseline
Follow-up
2 (0–8)a 0 (0–2)
2 (0–6) 0 (0–2)
1 (0–8)a 0 (0–3)
1 (0–7)a 0 (0–2)
a A group difference indicates that the CAI group failed more numbers of trials than the healthy control group.
studies previously assessed unipedal postural control following ankle joint cooling in healthy subjects [19,20]. They both reported that postural control in healthy subjects was not substantially affected after cryotherapy. Although the methodology of the two previous studies may be criticized, combined with the results of our current study with a more robust design and additional postural control measures, there appears to be mounting evidence indicating the ankle cryotherapy does not adversely affect postural control. One previous study [33] has examined the effects of cryotherapy on single leg balance in patients with lateral ankle sprains within the 4–7 days. The balance performance, as assessed by ML postural sway variability, was impaired following lower-leg immersion cryotherapy in which the injured ankle was immersed for 20 min in a tub containing an ice water mixture [33]. This result conflicts with our findings of no influence of ankle joint cooling on postural control in patients with CAI. This discrepancy may be due to the difference in body area being cooled (lower limb immersion versus focal cooling of the ankle joint) or the nature of the joint pathology (acute versus chronic) [33]. We attempted to locally cool the skin surface overlying the ankle joint with an ice bag because of previously reported favorable outcomes on muscle activation following cold application with an ice bag to a joint [8–14]. Our joint cooling technique significantly decreased only the joint surface, but not the soleus muscle surrounding the joint. In contrast, the immersion cooling technique used in the previous study likely cooled all structures in the lower leg including the entire foot, ankle, and extrinsic muscles and tendons in the lower leg. The immersion cryotherapy likely decreased sensitivity of cutaneous, articular, and musculotendinous receptors thus
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resulting in alterations in single leg balance [33–35]. Postural control impairments following the ice water immersion have also been found in healthy participants [36]. However, focal ankle joint cooling has not resulted in postural control deficits in healthy participants [19,20]. These results suggest that ice water immersion that cools both joints and their surrounding muscles may have different effects than focal joint cooling. We surmise that postural control in unipedal stance may be impaired following cooling the lower leg due to direct muscle cooling, but not after focally cooling the ankle joint. It is believed that the multiple sensory inputs from afferent structures in the ankle joint are necessary for the central nervous system (CNS) to execute successful postural control, and alterations in these sensory activities may cause alterations in postural control [2,25]. Three categories of mechanoreceptors responsible for sensing postural information to CNS in the ankle joint includes cutaneous, articular, and musculotendious receptors. It is reasonable to assume that both focal ankle joint cooling and ice water immersion would affect cutaneous, articular, and tendonous receptors on the anterolateral aspect of the ankle. The ice water immersion would also influence articular receptors elsewhere around the ankle and foot, but probably more importantly, it would also cool the muscle spindles in the intrinsic and extrinsic foot muscles. Muscles spindles, especially in the triceps surae, are extremely important in regulating postural control [34,35,37]. The study utilizing mechanical vibration applied to the triceps surae as a perturbing tool demonstrated considerable postural deviations, indicating a vital role of muscle spindles in contributing to proprioception that is essential for accurate postural control [38,39]. Thus, the differing results on postural control between focal ankle joint cooling and ice water immersion are likely due to the influence that postural control has on the muscle spindles. In addition to potential sensory effects of ankle joint cooling, there is evidence that ice bags applied to the knee or ankle joint significantly enhance motor function including muscle activation [8–13], muscle fiber nerve conduction velocity [13], force output [10,12,13], and functional performance [14]. It has been suggested that these improvements are due to increased motoneuron recruitment following joint cooling [10,11]. We hypothesized that ankle joint cryotherapy would enhance postural control in individuals both with and without CAI because the CNS would better accommodate to postural demands with the expanded alpha motoneuron pool of the ankle stabilizing muscles. However, our results did not support this hypothesis. One likely explanation for these results may be the absence of changes in motoneuron pool excitability (MNPE) of ankle muscles after the similar ice treatment while standing [40]. Recently, Kim et al. [40] assessed MNPE of the soleus and fibularis longus, as assessed by Hoffmann reflex while their subjects laid prone and then stood in bipedal and unipedal stances. They found a 20-min ice bag application to the ankle joint significantly increased MNPE in both muscles while prone in a manner consistent with previous investigations [8,9], but they did not find any changes in MNPE in either standing
Table 5 Skin surface temperatures (8C, mean and standard deviation). Group
Site
Ankle cryotherapy Baseline
Sham Follow-up
Baseline
Follow-up
a
Chronic ankle instability
Ankle Soleus Room
30.86 2.1 31.47 1.9 23.64 1.6
12.08 2.8 31.90 1.5 23.86 1.5
30.23 2.1 31.03 1.9 23.21 2.1
30.68 1.7 31.19 1.8 23.69 2.2
Healthy control
Ankle Soleus Room
30.49 1.7 30.92 1.9 22.95 1.8
12.21 2.7a 30.74 1.8 22.89 1.3
30.16 1.5 30.78 1.4 22.86 1.2
30.25 1.7 30.83 1.2 22.93 1.2
a
A difference indicates that ankle cryotherapy significantly decreased the skin surface overlying the ankle joint.
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postures after cryotherapy. These results indicate that the increased MNPE associated with ankle joint cooling found in a non-weight bearing position may not translate to weight bearing positions. This discrepancy may have important applications for the use of cryotherapy as a disinhibitory modality prior to therapeutic exercise. In addition to the neurophysiological explanations of our results, our methodological choices may have influenced our results. First, we used a 20-min ice bag application to the ankle joint while some authors [8–10] found improved muscle function with 30-min of cold application. However, it should be noted that 20-min of ice treatment has been shown to elicit MNPE of the soleus and fibularis longus in both individuals with and without CAI [40]. Secondly, it has been suggested that exercise intervention following an ice bag application to a joint would facilitate muscle function [10–12], but the present study did not include an exercise protocol because it focused on isolated effects of joint cooling on postural control. Finally, the present study did not utilize a true control condition (no intervention), but had two treatment conditions of cryotherapy and sham. In both conditions the bag containing either ice or candy corn was secured to the ankle with an elastic bandage. It is possible that joint compression with an elastic bandage may affect single leg balance performance, however, it must be noted that the compression wrap was removed when the treatment time elapsed and all balance testing was performed without compression. The results of the current study may be important in clinical settings where there is an impression of potential detrimental effects of cryotherapy on muscle function. We agree that direct muscle cooling may impair postural control [33,36], however, our results showed that focal cooling of the ankle joint did not impair postural control. It does not appear that cryotherapy to either the ankle joint or its surrounding musculature can enhance unipedal postural control. On the other hand, focal joint cooling may be safe to use prior to therapeutic exercises aimed at improving muscle activation and strength [10–13]. When cryotherapy is necessary in the beginning of a rehabilitation session, it is important to focus on ankle joint cooling to avoid deleterious effects on postural balance associated with more global cooling procedures including the surrounding muscles as would occur with cold water immersion. Surprisingly, we found an improvement in postural control regardless of which intervention was applied, as there was a significant decrease in the mean COP velocity after interventions. This result may reflect a learning effect and indicate the COP velocity measure may be more sensitive to change than other COP measures, requiring a practice trial. It is also possible to speculate that joint compression provided by elastic bandage used to secure a plastic bag of ice or candy corn (sham) plays a role in slowing the COP excursions. However, it is noted that the ankle joint was released from the compression during postural control assessments. In conclusion, we found that postural control during unipedal stance was impaired among individuals with CAI, but postural control was not altered following a 20-min focal ankle joint cooling in individuals both with and without CAI. These findings indicate that a single session of ankle joint cryotherapy is neither beneficial nor harmful for single leg balance performance. Acknowledgements National Athletic Trainers’ Association Research and Education Foundation funded the present study through Doctoral Grant Program. The study sponsor does not play any role in the study design, in the collection, analysis and interpretation of data, in the writing of the manuscript, and in the decision to submit the manuscript for publication.
Conflict of interest statement: There is no conflict of interests for any of the authors.
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