Technology and Health Care 22 (2014) 759–766 DOI 10.3233/THC-140849 IOS Press
759
Effects of motor-level transcutaneous electrical nerve stimulation on ipsilateral and un-stimulated contralateral quadriceps femoris Ayodele Teslim Onigbindea,∗, Opeyemi Oluwasanmi Adeloyea , Olubukola Akindoyina and Tarimo Nestob a Department
of Medical Rehabilitation, College of Health Sciences, Obafemi Awolowo University, Osun State, Nigeria b Malawi Against Physical Disabilities, Blantyre, Malawi Received 31 May 2014 Accepted 13 July 2014 Abstract. PURPOSE: There is a paucity of data on effects of motor-level stimulation using Transcutaneous Electrical Nerve Stimulator (TENS) on ipsilateral quadriceps femoris group of muscles. The effect is also unknown on the untrained contralateral quadriceps femoris. The primary purpose of this study was to determine the effect of TENS on quadriceps muscle strength at the stimulated ipsilateral and un-stimulated contra-lateral extremities. METHODS: Participants were 50 apparently healthy undergraduate. They were recruited using sample of convenience. The right quadriceps group of muscles were stimulated for 15 minutes twice a week for 8 weeks using motor-level stimulation parameters (frequency of 85 Hz and pulse width of 100 microseconds) while the left lower limbs (control) were not stimulated. The right and left quadriceps muscle strengths were quantified using tensiometer; at onset and after 8 weeks. The data were analysed using the descriptive and inferential statistics (paired t-test and ANOVA). Alpha level was set at 0.05. RESULTS: The initial and final left strengths of the un-stimulated quadriceps muscles were 311.46 ± 58.84N and 395.60 ± 100.71N at onset and after 8 weeks respectively. After 8 weeks the un-stimulated left quadriceps strength was significantly greater than the initial value (t = −7.63, p < 0.001). Similarly, the initial and final right quadriceps strength (stimulated limb) were 351.51 ± 117.68N and 471.31 ± 112.19N; at onset and after 8 weeks respectively. The post stimulation strength of the right quadriceps was also significantly higher than the pre-intervention strength (t = −10.25, p < 0.001). However, the increment in quadriceps strength between right and left extremities after 8 weeks was insignificant (t = −1.35, p = 0.18). There was also significant increase in the girth of the right quadriceps (t = −6.08, p = 0.001) after 8 weeks. CONCLUSION: We concluded that there were increments in both strength and muscle size of the stimulated right quadriceps using motor level stimulation parameters of TENS modality. The un-stimulated contralateral quadriceps strength also increased after 8 weeks. This implied that there was cross-training effect at the contralateral quadriceps group of muscles. Keywords: Quadriceps muscle, strength, cross-training, motor level stimulation TENS
∗ Corresponding author: Ayodele Teslim Onigbinde, Department of Medical Rehabilitation, College of Health Sciences, Obafemi Awolowo University, Ile-Ife, Osun State, Nigeria. E-mail: [email protected].
c 2014 – IOS Press and the authors. All rights reserved 0928-7329/14/$27.50
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A.T. Onigbinde et al. / Effects of motor-level TENS on quadriceps femoris
1. Introduction Muscular strength is considered as one of the factors being used to establish musculoskeletal fitness [3, 13]. Strengthening can be achieved using Electrical Muscle Stimulator (EMS), weight resisted programs such as bicep curl, dumb bell, and leg curl [7]. Conventionally, Transcutaneous Electrical Nerve Stimulator (TENS) modality with motor stimulation parameters is being speculated to improve muscle strength and this is suggesting that the electro-analgesic modality is having other indications other than pain modulation [8,11]. Previous studies have established the relevance of different types of TENS in reducing spasticity [15,22,27]. Kavac et al. [16] reported the efficacy of TENS in decreasing both sensory and motor impairments associated with diabetic polyneuropathy and this lent credence to previous reports of Watkins [28] and Apfel et al. [2] that it could affect changes at both sensory and motor systems of peripheral nerves. Early fifties and recently, muscle strengthening programmes such as isometric, isotonic, isokinetic, muscle settings, weight training, muscle conditioning and kinetic chain exercises had been established to improve strength [10,18]. Muscle strength training is effective for postural body alignment, increasing metabolism, and relieving stress [24]. Quadriceps group of muscles is a vital group of muscles responsible for flexion of the hip and knee extension [21] and it is of topmost importance for sporting activities and functional activities of daily living. Although, exercise is recommended most often for improving motor skills and bone strength but it appears the use of portable TENS is gaining increasing acceptance for muscle building. Safety and rigour of exercise strength training programme are discouraging factors, and improper execution and negligence of appropriate precautions can result in injury. In an old report by Kots [19], EMS was reported to be more effective than exercise alone in strengthening skeletal muscle in elite athletes and this might continue to influence researcher’s interest in future studies. Several manufacturers have continued to develop portable units which can generate different electrical wave forms to stimulate innervated muscles [23]. Most functions of these stimulators are propagated by manufacturing companies. There is limited evidence to ascertain claims of these companies [23]. Furthermore, several studies on strength training had established that un-exercised contra-lateral extremity gained increment in strength, and this is referred to as cross training or cross education effects [24, 26,29]. However, some findings could not establish this effect [13]. Transcutaneous Electrical Nerve Stimulation placed on motor point elicits muscle contraction depending on selected parameters such as frequency, pulse duration and intensity [30]. Motor-level stimulation effect of TENS is being speculated to have effect on muscular strength [17]. There are very few studies on cross training effects of electrical stimulation, aside this, there are also conflicting reports [5,25,29]. The primary purpose of this study was to determine the effect of motor-level stimulation on contralateral quadriceps muscles strength after 8 weeks TENS application on the ipsilateral quadriceps. Also, the study aimed to compare the differences in strength gained by both the stimulated and un-stimulated quadriceps. It was hypothesized that there would be no significant difference in the initial and final quadriceps muscle strength of the stimulated ipsilateral and un-stimulated contra-lateral quadriceps after 8 weeks; and there would be no significant difference in strength increment between the ipsilateral and contralateral quadriceps.
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2. Materials and methods 2.1. Subjects The participants in this study were 50 apparently healthy undergraduate physiotherapy students at Obafemi Awolowo University, Ile-Ife, Osun state. The study setting was the gymnasium of Medical rehabilitation department, Obafemi Awolowo University, Ile-Ife, Osun state, Nigeria. 2.2. Inclusion and exclusion criteria The subjects had no history of musculoskeletal dysfunctions and were afebrile during the period of the study. They were also not on narcotic drugs or any other performance enhancement drugs. Participants with respiratory disorders, hypertension, metallic implants, and with previous history of musculoskeletal dysfunctions were excluded from the study. 2.3. Sampling technique Sample of convenience was used for this study. 2.4. Research design The research design was a pre and post experimental design. 2.5. Instruments Transcutaneous Electrical Nerve Stimulator (TENS 7000 TM, Current Solution, LOT NO.2011-11, LLC 3814, Woodbury, TX, USA), a 9 Voltage stimulator was used to stimulate quadriceps group of muscles and cable tensiometer was used to quantify the isometric quadriceps muscle strength. The tensiometer was graded from 0 to 100 kgf but the values were converted to Newton (N) to have a grade of 0 to 980.67 N, (1 kgf = 9.8067 N). The tensiometer measured tension generated in the cable after being pulled. 2.6. Procedures The Research and ethics committee of the Institute of Public Health, Obafemi Awolowo University, Ile-Ife, Osun state, Nigeria (IPH/OAU/12/192) granted approval for the study. The purpose and procedures of the research were explained to each of the subject and written consent was also obtained. All participants were given orientation prior to the application of TENS. They wore short knickers and were positioned in supine lying during the application of TENS to the quadriceps muscle of dominant right lower limb (stimulated limb) while the left quadriceps muscles served as the un-stimulated extremity (control). Limb dominance was ascertained using the method of Balogun and Onigbinde [4]. The labile method of electrode placement (quadripolar technique) was used to stimulate the quadriceps muscle of the right lower extremity for 15 minute. There are 4 electrodes; each has an area of 5 × 5 cm2 and they were arranged to cover the largest bulk of the anterior thigh of subject. The TENS device was set to Strength duration 2 mode (motor stimulation) which consisted of automatic modulation intensity and pulse width of 70% range. The intensity are decreased by 70% while the pulse width increased by 70%
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A.T. Onigbinde et al. / Effects of motor-level TENS on quadriceps femoris Table 1 Physical characteristics of the subjects Variables Age (year) Height (m) Weight (kg) Body Mass Index (kg/m2 )
Mean 23.94 1.71 62.9 21.6
Standard deviation 2.13 0.07 4.04 1.79
Table 2 Comparison of initial and final quadriceps muscle strength Quadriceps strength Stimulated limb Un-stimulated limb
Stage Initial Final Initial Final
Mean (N) 351.51 471.31 311.46 395.60
SD 117.68 112.19 58.84 100.71
t
p-value
−10.25
0.001
−7.63
0.001
in 5 seconds, in the next 5 seconds, the intensity again increased by 70% while the pulse width decreased by 70%. Total cycle time was 10 seconds. Pulse rate was pre-set to 85 Hz and pulse width of 100 microseconds. The intensity was gradually increased until there was maximum tolerable strong contraction of the knee extensors muscles. If accommodation was observed the amplitude was further increased to produce strong contraction but at comfortable sensory level for each participants. The tensiometer was used to assess the quadriceps muscle strength while sitting on a testing table with a backrest, following the procedures described by Balogun and Onigbinde [4]. The subjects maintained 120 degrees hip joint extension and 60 degrees knee flexion. An ankle cuff was affixed and attached to cable tensiometer and the peak isometric force (N) was recorded. They were verbally motivated with the word “PULL” during Knee extension. For each subject; isometric quadriceps muscle strengths of the limbs were evaluated using tensiometer and standard protocols. For each measurement, two trials were carried out but the higher reading was used for data analysis. Adequate rest intervals were allowed between each measurement. The right quadriceps group of muscles were stimulated with TENS for 15 minutes twice a week for 8 weeks while the left served as control for the duration (non-stimulated quadriceps). The right and left quadriceps muscle strength were quantified at onset and at the end of the 8th week. All the participants were advised to refrain from sporting activities throughout the period of the study. 2.7. Data analysis The data were analysed using descriptive statistics and Parametric inferential statistics [paired t-test]. Alpha level was 0.05. The paired t-test was used to compare the muscle strength, and the increment between the right and left quadriceps. Analysis of variance (multiple regression analysis) was used to determine the contributions of independent variables to final right quadriceps strength.
3. Results The ages of participants ranged between 19 and 28 years with a mean of 23 ± 2.13 years. There are 38 male and 12 female participants. Other anthropometric parameters are presented in Table 1. The initial and final left quadriceps strengths (un-stimulated) were 311.46 ± 58.84 N and 395.60 ± 100.71 N; at
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Table 3 Result of ANOVA showing level of significance of the predictorsb Model Regression Residual Total
Sum of squares 4173.937 2238.883 6412.820
Df 7 42 49
Mean square 596.28 53.31
F 11.19
Sig. 0.001a
a Predictors: (Constant), Initial quadriceps strength, height, age, Girth, weight, BMI. (SEE = 8.04). b Dependent Variable: Final quadriceps strength.
Series 1
Fig. 1. Percentage increase in strength of right and left quadriceps strength.
onset and after 8 weeks respectively. This showed an increment of 27.0% (Fig. 1). The paired t-test showed that the increment was significant after 8 weeks (t = −7.63, p < 0.001). The initial and final right quadricep strengths (stimulated limb) were 351.51 ± 117.68 N and 471.31 ± 112.19 N; at onset and after 8 weeks respectively. Similarly, the paired t test showed that there was significant increment in the right quadriceps muscle strength after 8 weeks of motor level stimulation (t = −10.25, p < 0.001), with an increment of 34.1% strength (Table 2). However, there was no significant difference in the increment between right and left quadriceps strength after 8 weeks (t = −1.35, p = 0.18). There were significant differences between the right and left quadriceps strength at onset (t = 6.89, p < 0.001) and after 8 weeks (t = 5.66, p < 0.001). The mean initial and final girths of the right quadriceps were 48.96 (SD = 5.70) cm and 50.36 (SD = 5.96) cm after 8 week of TENS stimulation. The paired t-test showed that there was significant difference between the mean initial and final girths of the right quadriceps (t = −6.08, p = 0.001). The result of the multiple regression analysis showed that the initial right quadriceps strength was the most significant predictor of final right quadriceps muscle strength (F = 11.19, P = 0.001). The contributions of age, height, weight, BMI, girth and initial quadriceps strength (IQS) were found to be 0.2%, 1.0%, 3.8%, 0.5%, 3.1% and 54.0% respectively. The coefficient of determination (R2 ) for the independent variables was found to be 56.6%.
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4. Discussion The TENS modalities have relative effects on muscle strength but it depends on selected system units comprising of Strength duration, biphasic square and pulsatile current (frequency of 50 Hz, and phase duration of 85 µs and above) [30]. This study utilized 85 Hz and pulse width of 100 microseconds as stimulation parameters. Some studies have established the relevance of TENS in reducing spasticity of different group of muscles and in different pathologies [2,15,16,22,27,28]. This study found significant increase in muscle strengths of both the ipsilateral and contralateral quadriceps group of muscles after 8 weeks motor-level stimulation of the former using TENS. This is confirming transfer or cross-training effects at the contralateral quadriceps group. There are previous reports which had established cross training effects after volitional exercise trainings [24,26,29]. The strength attained at the un-stimulated contralateral muscle group was also comparable with strength achieved at the stimulated muscles of ipsilateral side as there was no significant difference in the percentage increments. This current finding corroborated that of Zhou et al. [33]. However, it contradicted that of Sariyildiz et al. [25] who found no increment in the contra-lateral strength, although, this was when the wrist flexors group of muscles were stimulated. Furthermore, our current findings confirmed the speculation of Miller et al. [22] and Kennedy et al. [17]; they reported efficacy of TENS in eliciting muscle contraction if appropriate parameters are selected to produce strong but comfortable muscle contraction [16]. Similarly, we noted that our finding was comparable to the effects of high resistant exercises training being utilized to improve muscle strength [1,20]. Similarly, there was significant increase in the bulkiness of the right quadriceps group of muscles after 8 weeks of motor-level stimulation, and this implied muscle hypertrophy. This contradicted the reports of Bemben and Murphy [5]; and Blazevich and Zhou [6]. During nerve stimulation, the largest-diameter muscle fibers were stimulated ahead of smaller-diameter muscle fibers but the recruitment pattern is reversed during volitional exercise where smallest alpha motor neurons were recruited first [23]. There are morphological and architectural changes in muscle structure using exercises but previous studies could not observe such developments with electrical stimulation [5,6]. Physiological changes noticed for exercise training includes increased hypertrophy and hyperplasia of muscle fibers; neural activation (firing and synchronization of more motor units); increased tensile strength of tendons, ligaments, and connective tissue [18]. In an extensive review by Zhou [32], he highlighted reports of different authors who offered explanations on changes in neural mechanism during electrical stimulation for cross education; Carr et al. [9] attributed it to bilateral co-activation of cortico-spinal tract; Yue and Cole [31] attributed it to diffusion of impulses between cerebral hemisphere while Horgtobagyi et al. [12] suggested activation of afferent modulation at the contra-lateral limb. We found that the initial right quadriceps strength was the most significant predictor of final right quadriceps muscle strength; while age, height, weight, BMI and girth contributed minimally as predictors. The coefficient of determination (R2 ) for the independent variables was found to be 56.5%. This implied that other variables are required for accurate prediction of quadriceps when TENS is being used as the strengthen tool. The standard error estimate (8.04) was considered high while coefficient of determination was considered to be low and these might be attributed to the small sample size and the narrow age range (19–28 years) of the sample. Our current findings have clinical implications, TENS modality, pre-set to motor-level stimulation parameters will be effective in strengthening quadriceps group of muscles; and the cross-training effect might be useful for stroke survivors, athletes and patients with unilateral injuries and cast immobilization. Yet, there are limitations of the study. First, the sample size was relatively low, although the results
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are significant. Furthermore, we did not measure the girth of the left quadriceps to establish possible (but rarely occurring) presence of hypertrophy at the un-stimulated quadriceps. We concluded that there were increments in both strength and muscle size of the stimulated right quadriceps using motor level stimulation parameters of TENS modality. The un-stimulated contralateral quadriceps strength also increased significantly after 8 weeks. This implied that there was cross-training effect at the contralateral quadriceps group of muscles. Similar study is recommended in the future using patients with orthopaedic and neurological impairments.
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22]
T Abe, DV DeHoyos, ML Pollock, L. Garzarella (2000). Time course for strength and muscle thickness changes following upper and lower body resistance training in men and women. Eur J Appl Physiol 81: 174. SC Apfel, AK Asbury, V Bril (2001). Positive neuropathic sensory symptoms as endpoints in diabetic neuropathy trials. J Neurol Sci 189: 3-5. JA. Balogun, AT Onigbinde. (1991). Predictors of the Elbow Flexors. And Knee Extensors isometric Strength in males Age 18-20. Journal of Physical Therapy Science, Vol. 3, 7-12. JA. Balogun, AT Onigbinde. (1992). Hand and Leg Dominance: Do they really Affect Limb Muscle Strength. Physiotherapy Theory and Practice 8, 89-96. Bemben and Murphy, 2001 in Zhou (2003). Cross education and neuromuscular adaptation during early stage of strength training. Journal of Exercise Science 1(1): 54-60. MG Blazevich, RE Zhou, (2002) in Zhou (2003). Cross education and neuromuscular adaptation during early stage of strength training. Journal of Exercise Science 1(1): 54-60. WJ Brown, C Finch, D Robbinson, M Torode, S White (2002). The benefits and risks of exercise during pregnancy. J Sci Med Sport 5(1): 11-9. TW Chiu, CW Hui-Chan, G Chein (2005). A randomized clinical trial of TENS and exercise for patients with chronic neck pain. Clin Rehabil. Dec, 19(8): 850-860. LJ Carr, LM Harrisson, JA Stephen (1994) in Zhou (2003). Cross education and neuromuscular adaptation during early stage of strength training. Journal of exercise science, 1 (1): 54-60. TL DeLorme, A Watkins (1951). Progressive Resistance Exercise. Appleton-Century, New York, 1951. J Hart, B Pietosimone, C Ingersoll (2010). Quadriceps activation following knee injuries: A systematic review. Journal of Athletic Training 45(1): 87-97. T Horgtobagyi, K Scott, J Lambert, G Hamilton, J Tracy (1999) in Zhou (2003). Cross education and neuromuscular adaptation during early stage of strength training. Journal of exercise science, 1 (1): 54-60. DJ Housh, TJ Housh, GO Johnson, W-K (1992) in Zhou (2003). Cross education and neuromuscular adaptation during early stage of strength training. Journal of exercise science, 1 (1): 54-60. MI Johnson, CH Ashton, JW Thompson (1991). An in-depth study of long-term users of transcutaneous electrical nerve stimulation (TENS): Implications for clinical use of TENS. Pain 44(3): 221-9. MR Joodaki, GR Olyaei, H Bagheri (2001). The effects of electrical nerve stimulation of the lower extremity on H-reflex and F-wave parameters. Electromyogr. Clin. Neurophysiol 4: 23-28. S Kavak, T Metinr, A Ömer (2010). Efficacy of Transcutaneous electrical nerve stimulation in alleviating impairment associated with diabetic polyneuropathy Cell Membranes and Free Radical Research Volume 2, Number 3, 112-116. P D Kennedy,P Lude, ML Elfstrom, EF Smithson (2011) Psychological contributions to functional independence: A longitudinal investigation of spinal cord injury rehabilitation. Arch Phys Med Rehabil 32: 597-601. C Kisner, LA Colby (2007). Therapeutic exercise: Foundations and techniques. 5th edition, F. A. Davis Company. 1915 Arch Street, Philadelphia, PA 19103, www.fadavis.com. Y Kots (1977). Electrostimulation. Symposium on Electrostimulation of Skeletal Muscles, Canadian Soviet Exchange Symposium,Concordia University, December 6–10. WJ Kraemer, JS Volek„ SJ Fleck (2001). Chronic musculoskeletal adaptations to resistance training. In Roitman, JL (ed) ACSM’s Resource Manual for Guidelines for Exercise Testing and Prescription, ed 4. Lippincott Williams and Wilkins, Philadelphia, p. 176. WD McGraw, FI Katch, V Katch (2001). Exercise Physiology: Energy, Nutrition, and Human Performance (5th edition). Baltimore: Lippincott Williams & Wilkins. L Miller, P Mattison, L Paul, L Wood (2007). The effect of Transcutaneous electrical nerve stimulation on spasticity in multiple sclerosis. Multi. scler 13, 527-536.
766 [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33]
A.T. Onigbinde et al. / Effects of motor-level TENS on quadriceps femoris JP Porcari, PM Karen, F Carl, K Thomas, C Ben, S Chad (2002). Effects of Electrical Muscle Stimulation on Body Composition, Muscle Strength, and Physical Appearance. Journal of Strength and Conditioning Research, 16(2), 165172. R Robergs, F Ghiasvand, D Parker (2004). Biochemistry of exercise-induced metabolic acidosis. Am J Physiol Regul Integr Comp Physiol 287(3): R502–16. doi:10.1152/ajpregu.00114PMID 15308499. M Sariyildiz, I Karachan, A Rezvani, O Ergin, M Cidem. (2011). Cross-education of muscle strength: cross training effects are not confined to untrained contra-lateral contra-lateralmuscle. Scandinavian journal of Medicine & Science in sports, vol21, 6, e359-e364. T Shield, S Zhou (1999). Effect of resistance training on the completeness of muscle activation, Book of Abstract, Fifth IOC World Congress on Sport Sciences (pp. 8). Sydney, Australia. L Sonde, H Kalino, M Vitanen (2000): Stimulation with High- frequency TENS Effects on lower limb spasticity after stroke. Advances in Physiotherapy 2: 183-7. PJ Watkins (1984). Somatic neuropathies. Diabetes Care 27: 1458-1486. JP Weir, D Housh, TJ Housh,LL Weir (1997). The effect of unilateral concentric weight training and detraining on joint angle specificity, cross-training, and the bilateral deficit. Journal of Orthopaedic & Sports Physical Therapy, 25(4), 264-270. Wikipedia.com (2013). Transcutaneous Electrical Nerve Stimulation. www.wikipedia. org. Accessed on 23rd May, 2014. G Yue, KJ Cole (1992) in Zhou (2003). Cross education and neuromuscular adaptation during early stage of strength training. Journal of Exercise Science, 1 (1): 54-60. S Zhou (2003). Cross education and neuromuscular adaptation during early stage of strength training. Journal of exercise science, 1 (1): 54-60. S Zhou, O Andrew, JD Allan (2002). Effects of unilateral, voluntary and electromyostimulation training on muscular strength on the contra-lateral limb. Hong Kong Journal of Sports Medicine and Sports Science, vol. XIV, pp. 1-11.
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759
Effects of motor-level transcutaneous electrical nerve stimulation on ipsilateral and un-stimulated contralateral quadriceps femoris Ayodele Teslim Onigbindea,∗, Opeyemi Oluwasanmi Adeloyea , Olubukola Akindoyina and Tarimo Nestob a Department
of Medical Rehabilitation, College of Health Sciences, Obafemi Awolowo University, Osun State, Nigeria b Malawi Against Physical Disabilities, Blantyre, Malawi Received 31 May 2014 Accepted 13 July 2014 Abstract. PURPOSE: There is a paucity of data on effects of motor-level stimulation using Transcutaneous Electrical Nerve Stimulator (TENS) on ipsilateral quadriceps femoris group of muscles. The effect is also unknown on the untrained contralateral quadriceps femoris. The primary purpose of this study was to determine the effect of TENS on quadriceps muscle strength at the stimulated ipsilateral and un-stimulated contra-lateral extremities. METHODS: Participants were 50 apparently healthy undergraduate. They were recruited using sample of convenience. The right quadriceps group of muscles were stimulated for 15 minutes twice a week for 8 weeks using motor-level stimulation parameters (frequency of 85 Hz and pulse width of 100 microseconds) while the left lower limbs (control) were not stimulated. The right and left quadriceps muscle strengths were quantified using tensiometer; at onset and after 8 weeks. The data were analysed using the descriptive and inferential statistics (paired t-test and ANOVA). Alpha level was set at 0.05. RESULTS: The initial and final left strengths of the un-stimulated quadriceps muscles were 311.46 ± 58.84N and 395.60 ± 100.71N at onset and after 8 weeks respectively. After 8 weeks the un-stimulated left quadriceps strength was significantly greater than the initial value (t = −7.63, p < 0.001). Similarly, the initial and final right quadriceps strength (stimulated limb) were 351.51 ± 117.68N and 471.31 ± 112.19N; at onset and after 8 weeks respectively. The post stimulation strength of the right quadriceps was also significantly higher than the pre-intervention strength (t = −10.25, p < 0.001). However, the increment in quadriceps strength between right and left extremities after 8 weeks was insignificant (t = −1.35, p = 0.18). There was also significant increase in the girth of the right quadriceps (t = −6.08, p = 0.001) after 8 weeks. CONCLUSION: We concluded that there were increments in both strength and muscle size of the stimulated right quadriceps using motor level stimulation parameters of TENS modality. The un-stimulated contralateral quadriceps strength also increased after 8 weeks. This implied that there was cross-training effect at the contralateral quadriceps group of muscles. Keywords: Quadriceps muscle, strength, cross-training, motor level stimulation TENS
∗ Corresponding author: Ayodele Teslim Onigbinde, Department of Medical Rehabilitation, College of Health Sciences, Obafemi Awolowo University, Ile-Ife, Osun State, Nigeria. E-mail: [email protected].
c 2014 – IOS Press and the authors. All rights reserved 0928-7329/14/$27.50
760
A.T. Onigbinde et al. / Effects of motor-level TENS on quadriceps femoris
1. Introduction Muscular strength is considered as one of the factors being used to establish musculoskeletal fitness [3, 13]. Strengthening can be achieved using Electrical Muscle Stimulator (EMS), weight resisted programs such as bicep curl, dumb bell, and leg curl [7]. Conventionally, Transcutaneous Electrical Nerve Stimulator (TENS) modality with motor stimulation parameters is being speculated to improve muscle strength and this is suggesting that the electro-analgesic modality is having other indications other than pain modulation [8,11]. Previous studies have established the relevance of different types of TENS in reducing spasticity [15,22,27]. Kavac et al. [16] reported the efficacy of TENS in decreasing both sensory and motor impairments associated with diabetic polyneuropathy and this lent credence to previous reports of Watkins [28] and Apfel et al. [2] that it could affect changes at both sensory and motor systems of peripheral nerves. Early fifties and recently, muscle strengthening programmes such as isometric, isotonic, isokinetic, muscle settings, weight training, muscle conditioning and kinetic chain exercises had been established to improve strength [10,18]. Muscle strength training is effective for postural body alignment, increasing metabolism, and relieving stress [24]. Quadriceps group of muscles is a vital group of muscles responsible for flexion of the hip and knee extension [21] and it is of topmost importance for sporting activities and functional activities of daily living. Although, exercise is recommended most often for improving motor skills and bone strength but it appears the use of portable TENS is gaining increasing acceptance for muscle building. Safety and rigour of exercise strength training programme are discouraging factors, and improper execution and negligence of appropriate precautions can result in injury. In an old report by Kots [19], EMS was reported to be more effective than exercise alone in strengthening skeletal muscle in elite athletes and this might continue to influence researcher’s interest in future studies. Several manufacturers have continued to develop portable units which can generate different electrical wave forms to stimulate innervated muscles [23]. Most functions of these stimulators are propagated by manufacturing companies. There is limited evidence to ascertain claims of these companies [23]. Furthermore, several studies on strength training had established that un-exercised contra-lateral extremity gained increment in strength, and this is referred to as cross training or cross education effects [24, 26,29]. However, some findings could not establish this effect [13]. Transcutaneous Electrical Nerve Stimulation placed on motor point elicits muscle contraction depending on selected parameters such as frequency, pulse duration and intensity [30]. Motor-level stimulation effect of TENS is being speculated to have effect on muscular strength [17]. There are very few studies on cross training effects of electrical stimulation, aside this, there are also conflicting reports [5,25,29]. The primary purpose of this study was to determine the effect of motor-level stimulation on contralateral quadriceps muscles strength after 8 weeks TENS application on the ipsilateral quadriceps. Also, the study aimed to compare the differences in strength gained by both the stimulated and un-stimulated quadriceps. It was hypothesized that there would be no significant difference in the initial and final quadriceps muscle strength of the stimulated ipsilateral and un-stimulated contra-lateral quadriceps after 8 weeks; and there would be no significant difference in strength increment between the ipsilateral and contralateral quadriceps.
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2. Materials and methods 2.1. Subjects The participants in this study were 50 apparently healthy undergraduate physiotherapy students at Obafemi Awolowo University, Ile-Ife, Osun state. The study setting was the gymnasium of Medical rehabilitation department, Obafemi Awolowo University, Ile-Ife, Osun state, Nigeria. 2.2. Inclusion and exclusion criteria The subjects had no history of musculoskeletal dysfunctions and were afebrile during the period of the study. They were also not on narcotic drugs or any other performance enhancement drugs. Participants with respiratory disorders, hypertension, metallic implants, and with previous history of musculoskeletal dysfunctions were excluded from the study. 2.3. Sampling technique Sample of convenience was used for this study. 2.4. Research design The research design was a pre and post experimental design. 2.5. Instruments Transcutaneous Electrical Nerve Stimulator (TENS 7000 TM, Current Solution, LOT NO.2011-11, LLC 3814, Woodbury, TX, USA), a 9 Voltage stimulator was used to stimulate quadriceps group of muscles and cable tensiometer was used to quantify the isometric quadriceps muscle strength. The tensiometer was graded from 0 to 100 kgf but the values were converted to Newton (N) to have a grade of 0 to 980.67 N, (1 kgf = 9.8067 N). The tensiometer measured tension generated in the cable after being pulled. 2.6. Procedures The Research and ethics committee of the Institute of Public Health, Obafemi Awolowo University, Ile-Ife, Osun state, Nigeria (IPH/OAU/12/192) granted approval for the study. The purpose and procedures of the research were explained to each of the subject and written consent was also obtained. All participants were given orientation prior to the application of TENS. They wore short knickers and were positioned in supine lying during the application of TENS to the quadriceps muscle of dominant right lower limb (stimulated limb) while the left quadriceps muscles served as the un-stimulated extremity (control). Limb dominance was ascertained using the method of Balogun and Onigbinde [4]. The labile method of electrode placement (quadripolar technique) was used to stimulate the quadriceps muscle of the right lower extremity for 15 minute. There are 4 electrodes; each has an area of 5 × 5 cm2 and they were arranged to cover the largest bulk of the anterior thigh of subject. The TENS device was set to Strength duration 2 mode (motor stimulation) which consisted of automatic modulation intensity and pulse width of 70% range. The intensity are decreased by 70% while the pulse width increased by 70%
762
A.T. Onigbinde et al. / Effects of motor-level TENS on quadriceps femoris Table 1 Physical characteristics of the subjects Variables Age (year) Height (m) Weight (kg) Body Mass Index (kg/m2 )
Mean 23.94 1.71 62.9 21.6
Standard deviation 2.13 0.07 4.04 1.79
Table 2 Comparison of initial and final quadriceps muscle strength Quadriceps strength Stimulated limb Un-stimulated limb
Stage Initial Final Initial Final
Mean (N) 351.51 471.31 311.46 395.60
SD 117.68 112.19 58.84 100.71
t
p-value
−10.25
0.001
−7.63
0.001
in 5 seconds, in the next 5 seconds, the intensity again increased by 70% while the pulse width decreased by 70%. Total cycle time was 10 seconds. Pulse rate was pre-set to 85 Hz and pulse width of 100 microseconds. The intensity was gradually increased until there was maximum tolerable strong contraction of the knee extensors muscles. If accommodation was observed the amplitude was further increased to produce strong contraction but at comfortable sensory level for each participants. The tensiometer was used to assess the quadriceps muscle strength while sitting on a testing table with a backrest, following the procedures described by Balogun and Onigbinde [4]. The subjects maintained 120 degrees hip joint extension and 60 degrees knee flexion. An ankle cuff was affixed and attached to cable tensiometer and the peak isometric force (N) was recorded. They were verbally motivated with the word “PULL” during Knee extension. For each subject; isometric quadriceps muscle strengths of the limbs were evaluated using tensiometer and standard protocols. For each measurement, two trials were carried out but the higher reading was used for data analysis. Adequate rest intervals were allowed between each measurement. The right quadriceps group of muscles were stimulated with TENS for 15 minutes twice a week for 8 weeks while the left served as control for the duration (non-stimulated quadriceps). The right and left quadriceps muscle strength were quantified at onset and at the end of the 8th week. All the participants were advised to refrain from sporting activities throughout the period of the study. 2.7. Data analysis The data were analysed using descriptive statistics and Parametric inferential statistics [paired t-test]. Alpha level was 0.05. The paired t-test was used to compare the muscle strength, and the increment between the right and left quadriceps. Analysis of variance (multiple regression analysis) was used to determine the contributions of independent variables to final right quadriceps strength.
3. Results The ages of participants ranged between 19 and 28 years with a mean of 23 ± 2.13 years. There are 38 male and 12 female participants. Other anthropometric parameters are presented in Table 1. The initial and final left quadriceps strengths (un-stimulated) were 311.46 ± 58.84 N and 395.60 ± 100.71 N; at
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Table 3 Result of ANOVA showing level of significance of the predictorsb Model Regression Residual Total
Sum of squares 4173.937 2238.883 6412.820
Df 7 42 49
Mean square 596.28 53.31
F 11.19
Sig. 0.001a
a Predictors: (Constant), Initial quadriceps strength, height, age, Girth, weight, BMI. (SEE = 8.04). b Dependent Variable: Final quadriceps strength.
Series 1
Fig. 1. Percentage increase in strength of right and left quadriceps strength.
onset and after 8 weeks respectively. This showed an increment of 27.0% (Fig. 1). The paired t-test showed that the increment was significant after 8 weeks (t = −7.63, p < 0.001). The initial and final right quadricep strengths (stimulated limb) were 351.51 ± 117.68 N and 471.31 ± 112.19 N; at onset and after 8 weeks respectively. Similarly, the paired t test showed that there was significant increment in the right quadriceps muscle strength after 8 weeks of motor level stimulation (t = −10.25, p < 0.001), with an increment of 34.1% strength (Table 2). However, there was no significant difference in the increment between right and left quadriceps strength after 8 weeks (t = −1.35, p = 0.18). There were significant differences between the right and left quadriceps strength at onset (t = 6.89, p < 0.001) and after 8 weeks (t = 5.66, p < 0.001). The mean initial and final girths of the right quadriceps were 48.96 (SD = 5.70) cm and 50.36 (SD = 5.96) cm after 8 week of TENS stimulation. The paired t-test showed that there was significant difference between the mean initial and final girths of the right quadriceps (t = −6.08, p = 0.001). The result of the multiple regression analysis showed that the initial right quadriceps strength was the most significant predictor of final right quadriceps muscle strength (F = 11.19, P = 0.001). The contributions of age, height, weight, BMI, girth and initial quadriceps strength (IQS) were found to be 0.2%, 1.0%, 3.8%, 0.5%, 3.1% and 54.0% respectively. The coefficient of determination (R2 ) for the independent variables was found to be 56.6%.
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4. Discussion The TENS modalities have relative effects on muscle strength but it depends on selected system units comprising of Strength duration, biphasic square and pulsatile current (frequency of 50 Hz, and phase duration of 85 µs and above) [30]. This study utilized 85 Hz and pulse width of 100 microseconds as stimulation parameters. Some studies have established the relevance of TENS in reducing spasticity of different group of muscles and in different pathologies [2,15,16,22,27,28]. This study found significant increase in muscle strengths of both the ipsilateral and contralateral quadriceps group of muscles after 8 weeks motor-level stimulation of the former using TENS. This is confirming transfer or cross-training effects at the contralateral quadriceps group. There are previous reports which had established cross training effects after volitional exercise trainings [24,26,29]. The strength attained at the un-stimulated contralateral muscle group was also comparable with strength achieved at the stimulated muscles of ipsilateral side as there was no significant difference in the percentage increments. This current finding corroborated that of Zhou et al. [33]. However, it contradicted that of Sariyildiz et al. [25] who found no increment in the contra-lateral strength, although, this was when the wrist flexors group of muscles were stimulated. Furthermore, our current findings confirmed the speculation of Miller et al. [22] and Kennedy et al. [17]; they reported efficacy of TENS in eliciting muscle contraction if appropriate parameters are selected to produce strong but comfortable muscle contraction [16]. Similarly, we noted that our finding was comparable to the effects of high resistant exercises training being utilized to improve muscle strength [1,20]. Similarly, there was significant increase in the bulkiness of the right quadriceps group of muscles after 8 weeks of motor-level stimulation, and this implied muscle hypertrophy. This contradicted the reports of Bemben and Murphy [5]; and Blazevich and Zhou [6]. During nerve stimulation, the largest-diameter muscle fibers were stimulated ahead of smaller-diameter muscle fibers but the recruitment pattern is reversed during volitional exercise where smallest alpha motor neurons were recruited first [23]. There are morphological and architectural changes in muscle structure using exercises but previous studies could not observe such developments with electrical stimulation [5,6]. Physiological changes noticed for exercise training includes increased hypertrophy and hyperplasia of muscle fibers; neural activation (firing and synchronization of more motor units); increased tensile strength of tendons, ligaments, and connective tissue [18]. In an extensive review by Zhou [32], he highlighted reports of different authors who offered explanations on changes in neural mechanism during electrical stimulation for cross education; Carr et al. [9] attributed it to bilateral co-activation of cortico-spinal tract; Yue and Cole [31] attributed it to diffusion of impulses between cerebral hemisphere while Horgtobagyi et al. [12] suggested activation of afferent modulation at the contra-lateral limb. We found that the initial right quadriceps strength was the most significant predictor of final right quadriceps muscle strength; while age, height, weight, BMI and girth contributed minimally as predictors. The coefficient of determination (R2 ) for the independent variables was found to be 56.5%. This implied that other variables are required for accurate prediction of quadriceps when TENS is being used as the strengthen tool. The standard error estimate (8.04) was considered high while coefficient of determination was considered to be low and these might be attributed to the small sample size and the narrow age range (19–28 years) of the sample. Our current findings have clinical implications, TENS modality, pre-set to motor-level stimulation parameters will be effective in strengthening quadriceps group of muscles; and the cross-training effect might be useful for stroke survivors, athletes and patients with unilateral injuries and cast immobilization. Yet, there are limitations of the study. First, the sample size was relatively low, although the results
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are significant. Furthermore, we did not measure the girth of the left quadriceps to establish possible (but rarely occurring) presence of hypertrophy at the un-stimulated quadriceps. We concluded that there were increments in both strength and muscle size of the stimulated right quadriceps using motor level stimulation parameters of TENS modality. The un-stimulated contralateral quadriceps strength also increased significantly after 8 weeks. This implied that there was cross-training effect at the contralateral quadriceps group of muscles. Similar study is recommended in the future using patients with orthopaedic and neurological impairments.
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