Journal of Sport Rehabilitation, 2015, 24, 151 -155 http://dx.doi.org/10.1123/jsr.2013-0131 © 2015 Human Kinetics, Inc.
ORIGINAL RESEARCH REPORT
Validity and Reliability of Maximal-Strength Assessment of Knee Flexors and Extensors Using Elastic Bands Kenny Guex, Chantal Daucourt, and Stéphane Borloz Context: In the field of sport rehabilitation, an easy, valid, and reliable assessment of maximal strength is crucial for efficient muscle rehabilitation. Classically, it is performed on fitness equipment that is not necessary available in the field. Thera-Band has developed elastic bands with different resistances depending on the color of the band and on the percentage of its stretch. This may allow testing maximal strength. Objective: To determine validity and reliability of maximal-strength assessment of knee flexors and extensors using elastic bands. Design: Reliability and validity study. Participants: 22 healthy participants (31.3 ± 7.0 y, 175.5 ± 8.5 cm, 70.7 ± 12.9 kg). Intervention: Participants performed 2 maximal-strength assessments, separated by 7 d, of the knee flexors and extensors using elastic bands. After the 2nd trial, a maximal concentric isokinetic test at 60°/s was performed. Main Outcome Measures: Correlations between 1-repetition maximum using elastic bands and peak torque on an isokinetic dynamometer were used to determine the validity of the proposed method, while ICC, CV, and SEM were used to determine reliability between the 1st and 2nd trials. Results: The validity of the proposed method was found to be very high (r = .93 for both knee flexors and extensors). The relative reliability was found to be very high (ICC = .98 and .99 for knee flexors and extensors, respectively), while absolute reliability was also very satisfying (CV = 3.44% and 2.33%; SEM = 1.70 and 2.16 kg for knee flexors and extensors, respectively). Conclusions: Thera-Band is a valid and reliable alternative to the use of fitness equipment to test maximal strength of the knee flexors and extensors in healthy subjects. The ease of use, accessibility, and low cost of elastic bands should allow regular assessment during the rehabilitation process. Keywords: hamstring, quadriceps, force, evaluation Recovering muscle strength is one of the most important factors in sport rehabilitation. To reach the defined goal (eg, maximal strength, hypertrophy), different protocols specifying the number of repetitions and sets, with a load selected in percentage of the maximal strength, have been described.1 During rehabilitation, maximal strength may change rapidly and thus should be tested repeatedly to adjust the loads. Therefore, an easy, valid, and reliable assessment of maximal strength is crucial for efficient muscle rehabilitation. Isokinetic dynamometry, which has been shown to be valid and reliable, is considered the “gold standard” method for assessing muscle strength.2 However, availability of this evaluation system is limited, mainly because of its significant cost. On fitness equipment, maximal strength can be found using the 1-repetitionmaximum (1-RM) test. This is a valid and reliable Guex is with the Dept of Physiotherapy, University of Applied Sciences Western Switzerland, Lausanne, Switzerland. Daucourt and Borloz are with the Swiss Olympic Medical Center, CHUV-DAL, Lausanne, Switzerland. Address author correspondence to Kenny Guex at [email protected].
method.3 However, in the context of rehabilitation, this assessment could be inappropriate, since an attempt using maximum resistance is required. Therefore, a repetitionsto-fatigue test has been proposed. This method uses a prediction equation to find the 1-RM through submaximal testing based on the practically linear relationship between strength and anaerobic endurance for sets up to 10 repetitions.4 This method has been shown to be accurate to predict 1-RM.5 Elastic bands are commonly used during rehabilitation for muscle strengthening and are available in most rehabilitation centers. Thera-Band has developed bands with different color-coded resistance levels (yellow, red, green, blue, black, silver, and gold). For each color, this resistance can be measured in kilograms depending on the percentage that the band is stretched from its resting length.6 Regardless of how long the band is before it is stretched, the force produced at its stretched length depends on the percentage elongation. Hence, as with fitness equipment, muscle strength could be assessed using elastic bands. Therefore, the aim of the current study was to determine the validity and reliability of maximal-strength assessment of the knee flexors and extensors using elastic bands in healthy subjects.
151
152 Guex, Daucourt, and Borloz
Methods Twenty-two healthy recreational athletes (10 women, 12 men; 31.3 ± 7.0 y, 175.5 ± 8.5 cm, 70.7 ± 12.9 kg) were recruited for this study. The study was conducted according to the Declaration of Helsinki. Ethical approval was obtained from the local committee on human research. Participants signed an informed consent after explanation of the study protocol, data-collection procedures, and significance of the study objectives.
Downloaded by Northern Illinois University on 09/16/16, Volume 24, Article Number 2
Procedures The testing procedures were administered to all participants by the same investigator. During the first visit, maximal strength of knee flexors and extensors was assessed using elastic bands (Thera-Band GmbH, Hadamar, Germany). Then, a familiarization on an isokinetic dynamometer (Biodex System 2, Biodex Medical Systems, Shirley, NY, USA) was performed. Seven days afterward, maximal strength of the knee flexors and extensors was assessed using elastic bands following the same procedure. Then, maximal isokinetic strength of the knee flexors and extensors was assessed on the isokinetic dynamometer. Participants were all tested on their dominant side. Maximal-strength testing using elastic bands and isokinetic dynamometer were both performed on
the Biodex seat. Knee range of motion was 90° for all assessments (ie, 0–90° of knee flexion). During all tests, participants were asked to fold their arms across their chest (Figure 1). Maximal-Strength Assessment Using Elastic Bands. Thera-Band elastic bands provide a consistent,
linear, and predictable increase in resistance with elongation across all colors.6 Regression equations were proposed to quantify this resistance in kilograms based on the percentage of elongation.6 These equations were used to quantify the resistances “lifted” by the participants at end range of motion. Before the testing period, 15 different elastic bands were prepared (Table 1). After a 10-minute warm-up on a cycle ergometer (60 rpm, 80 W), participants were placed on the Biodex seat. Stabilization straps were positioned across their chest, pelvis, and ipsilateral thigh. To assess knee flexors, the Biodex seat was facing a wooden bar, while it was facing away from the wooden bar for testing of the knee extensors (Figure 1[A–B]). 1-RM of knee flexors and extensors was predicted using a repetitions-to-fatigue test. Participants were asked to perform a maximum of repetitions with an intermediate-resistance elastic band (ie, black Thera-Band). If they succeeded in performing 11 repetitions, a greaterresistance elastic band was selected for the next attempt.
Figure 1 — Maximal strength testing of knee (A) flexors and (B) extensors using elastic bands and (C) isokinetic assessment of knee flexors and extensors in concentric mode at 60°/s. To assess the knee flexors, the elastic band was fixed just proximal to the lateral malleolus of the participants and on the wooden bar ~90 cm above the knee and ~60 cm in front of this articulation. To assess the knee extensors, the elastic band was fixed just proximal to the lateral malleolus of the participants and on the wooden bar ~40 cm below the knee and ~160 cm behind this articulation.
JSR Vol. 24, No. 2, 2015
Maximal-Strength Testing Using Elastic Bands 153
Table 1 Resistances (kg) of the Prepared Elastic Bands for Knee-Flexor and -Extensor Maximal-Strength Assessments Knee Flexors Thera-Band color Black
Downloaded by Northern Illinois University on 09/16/16, Volume 24, Article Number 2
Silver
Gold
Knee Extensors
Number of layers
Initial length (cm)
Terminal length (%)
Resistance (kg)
Terminal length (%)
Resistance (kg)
4
70
101
16.6
160
22.9
65
116
18.2
180
25.0
60
134
20.2
203
27.5
75
88
20.9
143
29.5
70
101
23.0
160
32.2
65
116
25.4
180
35.3
60
134
28.2
203
38.9
55
156
31.5
231
43.2
75
88
33.9
143
47.4
70
101
37.2
160
51.7
65
116
41.0
180
56.5
60
134
45.4
203
62.3
55
156
50.6
231
69.0
50
181
56.9
264
77.1
45
213
64.5
304
87.0
4
4
Note: The resistances ranged from 16.6 to 56.9 kg for the knee flexors and from 22.9 to 77.1 kg for the knee extensors.
This procedure was repeated (maximum 5 attempts with 5 min rest between attempts) until the participant succeeded in performing 10 or fewer repetitions.4 The following prediction equation was then used4: 1RM = resistance in kg/(1.0278 – [0.0278 × reps]). Isokinetic Assessment. The dynamometer was calibrated according to the manufacturer’s recommendations and following the instructions for optimal reproducibility. The lever-arm shin pad was positioned just proximal to the lateral malleolus of the participant. During the first visit, participants performed a familiarization on the isokinetic dynamometer, which consisted of 10 concentric knee flexion-extensions at 60°/s. At the end of the second trial, participants performed 5 maximum concentric knee flexion-extensions of the dominant leg at 60°/s (Figure 1[C]). Peak torque (PT) for each movement was considered the greatest PT production over the 5 repetitions.
Statistical Analysis Mean ± SD values were calculated for all assessments. Validity of maximal-strength assessments of the knee flexors and extensors using elastic bands was explored by calculating Pearson correlation coefficients between 1-RM of the second trial and concentric PT. As general rule, we considered correlation coefficients >.90 very high, .70 to .89 high, and .50 to .69 moderate.7 Relative reliability of maximal-strength assessments using elastic bands was calculated with the intraclass
correlation coefficient (ICC2,1) between the 2 trials. ICC values were interpreted in the same way as the Pearson correlation coefficients. Absolute reliability was calculated with the coefficient of variation (CV). An analytical goal of
ORIGINAL RESEARCH REPORT
Validity and Reliability of Maximal-Strength Assessment of Knee Flexors and Extensors Using Elastic Bands Kenny Guex, Chantal Daucourt, and Stéphane Borloz Context: In the field of sport rehabilitation, an easy, valid, and reliable assessment of maximal strength is crucial for efficient muscle rehabilitation. Classically, it is performed on fitness equipment that is not necessary available in the field. Thera-Band has developed elastic bands with different resistances depending on the color of the band and on the percentage of its stretch. This may allow testing maximal strength. Objective: To determine validity and reliability of maximal-strength assessment of knee flexors and extensors using elastic bands. Design: Reliability and validity study. Participants: 22 healthy participants (31.3 ± 7.0 y, 175.5 ± 8.5 cm, 70.7 ± 12.9 kg). Intervention: Participants performed 2 maximal-strength assessments, separated by 7 d, of the knee flexors and extensors using elastic bands. After the 2nd trial, a maximal concentric isokinetic test at 60°/s was performed. Main Outcome Measures: Correlations between 1-repetition maximum using elastic bands and peak torque on an isokinetic dynamometer were used to determine the validity of the proposed method, while ICC, CV, and SEM were used to determine reliability between the 1st and 2nd trials. Results: The validity of the proposed method was found to be very high (r = .93 for both knee flexors and extensors). The relative reliability was found to be very high (ICC = .98 and .99 for knee flexors and extensors, respectively), while absolute reliability was also very satisfying (CV = 3.44% and 2.33%; SEM = 1.70 and 2.16 kg for knee flexors and extensors, respectively). Conclusions: Thera-Band is a valid and reliable alternative to the use of fitness equipment to test maximal strength of the knee flexors and extensors in healthy subjects. The ease of use, accessibility, and low cost of elastic bands should allow regular assessment during the rehabilitation process. Keywords: hamstring, quadriceps, force, evaluation Recovering muscle strength is one of the most important factors in sport rehabilitation. To reach the defined goal (eg, maximal strength, hypertrophy), different protocols specifying the number of repetitions and sets, with a load selected in percentage of the maximal strength, have been described.1 During rehabilitation, maximal strength may change rapidly and thus should be tested repeatedly to adjust the loads. Therefore, an easy, valid, and reliable assessment of maximal strength is crucial for efficient muscle rehabilitation. Isokinetic dynamometry, which has been shown to be valid and reliable, is considered the “gold standard” method for assessing muscle strength.2 However, availability of this evaluation system is limited, mainly because of its significant cost. On fitness equipment, maximal strength can be found using the 1-repetitionmaximum (1-RM) test. This is a valid and reliable Guex is with the Dept of Physiotherapy, University of Applied Sciences Western Switzerland, Lausanne, Switzerland. Daucourt and Borloz are with the Swiss Olympic Medical Center, CHUV-DAL, Lausanne, Switzerland. Address author correspondence to Kenny Guex at [email protected].
method.3 However, in the context of rehabilitation, this assessment could be inappropriate, since an attempt using maximum resistance is required. Therefore, a repetitionsto-fatigue test has been proposed. This method uses a prediction equation to find the 1-RM through submaximal testing based on the practically linear relationship between strength and anaerobic endurance for sets up to 10 repetitions.4 This method has been shown to be accurate to predict 1-RM.5 Elastic bands are commonly used during rehabilitation for muscle strengthening and are available in most rehabilitation centers. Thera-Band has developed bands with different color-coded resistance levels (yellow, red, green, blue, black, silver, and gold). For each color, this resistance can be measured in kilograms depending on the percentage that the band is stretched from its resting length.6 Regardless of how long the band is before it is stretched, the force produced at its stretched length depends on the percentage elongation. Hence, as with fitness equipment, muscle strength could be assessed using elastic bands. Therefore, the aim of the current study was to determine the validity and reliability of maximal-strength assessment of the knee flexors and extensors using elastic bands in healthy subjects.
151
152 Guex, Daucourt, and Borloz
Methods Twenty-two healthy recreational athletes (10 women, 12 men; 31.3 ± 7.0 y, 175.5 ± 8.5 cm, 70.7 ± 12.9 kg) were recruited for this study. The study was conducted according to the Declaration of Helsinki. Ethical approval was obtained from the local committee on human research. Participants signed an informed consent after explanation of the study protocol, data-collection procedures, and significance of the study objectives.
Downloaded by Northern Illinois University on 09/16/16, Volume 24, Article Number 2
Procedures The testing procedures were administered to all participants by the same investigator. During the first visit, maximal strength of knee flexors and extensors was assessed using elastic bands (Thera-Band GmbH, Hadamar, Germany). Then, a familiarization on an isokinetic dynamometer (Biodex System 2, Biodex Medical Systems, Shirley, NY, USA) was performed. Seven days afterward, maximal strength of the knee flexors and extensors was assessed using elastic bands following the same procedure. Then, maximal isokinetic strength of the knee flexors and extensors was assessed on the isokinetic dynamometer. Participants were all tested on their dominant side. Maximal-strength testing using elastic bands and isokinetic dynamometer were both performed on
the Biodex seat. Knee range of motion was 90° for all assessments (ie, 0–90° of knee flexion). During all tests, participants were asked to fold their arms across their chest (Figure 1). Maximal-Strength Assessment Using Elastic Bands. Thera-Band elastic bands provide a consistent,
linear, and predictable increase in resistance with elongation across all colors.6 Regression equations were proposed to quantify this resistance in kilograms based on the percentage of elongation.6 These equations were used to quantify the resistances “lifted” by the participants at end range of motion. Before the testing period, 15 different elastic bands were prepared (Table 1). After a 10-minute warm-up on a cycle ergometer (60 rpm, 80 W), participants were placed on the Biodex seat. Stabilization straps were positioned across their chest, pelvis, and ipsilateral thigh. To assess knee flexors, the Biodex seat was facing a wooden bar, while it was facing away from the wooden bar for testing of the knee extensors (Figure 1[A–B]). 1-RM of knee flexors and extensors was predicted using a repetitions-to-fatigue test. Participants were asked to perform a maximum of repetitions with an intermediate-resistance elastic band (ie, black Thera-Band). If they succeeded in performing 11 repetitions, a greaterresistance elastic band was selected for the next attempt.
Figure 1 — Maximal strength testing of knee (A) flexors and (B) extensors using elastic bands and (C) isokinetic assessment of knee flexors and extensors in concentric mode at 60°/s. To assess the knee flexors, the elastic band was fixed just proximal to the lateral malleolus of the participants and on the wooden bar ~90 cm above the knee and ~60 cm in front of this articulation. To assess the knee extensors, the elastic band was fixed just proximal to the lateral malleolus of the participants and on the wooden bar ~40 cm below the knee and ~160 cm behind this articulation.
JSR Vol. 24, No. 2, 2015
Maximal-Strength Testing Using Elastic Bands 153
Table 1 Resistances (kg) of the Prepared Elastic Bands for Knee-Flexor and -Extensor Maximal-Strength Assessments Knee Flexors Thera-Band color Black
Downloaded by Northern Illinois University on 09/16/16, Volume 24, Article Number 2
Silver
Gold
Knee Extensors
Number of layers
Initial length (cm)
Terminal length (%)
Resistance (kg)
Terminal length (%)
Resistance (kg)
4
70
101
16.6
160
22.9
65
116
18.2
180
25.0
60
134
20.2
203
27.5
75
88
20.9
143
29.5
70
101
23.0
160
32.2
65
116
25.4
180
35.3
60
134
28.2
203
38.9
55
156
31.5
231
43.2
75
88
33.9
143
47.4
70
101
37.2
160
51.7
65
116
41.0
180
56.5
60
134
45.4
203
62.3
55
156
50.6
231
69.0
50
181
56.9
264
77.1
45
213
64.5
304
87.0
4
4
Note: The resistances ranged from 16.6 to 56.9 kg for the knee flexors and from 22.9 to 77.1 kg for the knee extensors.
This procedure was repeated (maximum 5 attempts with 5 min rest between attempts) until the participant succeeded in performing 10 or fewer repetitions.4 The following prediction equation was then used4: 1RM = resistance in kg/(1.0278 – [0.0278 × reps]). Isokinetic Assessment. The dynamometer was calibrated according to the manufacturer’s recommendations and following the instructions for optimal reproducibility. The lever-arm shin pad was positioned just proximal to the lateral malleolus of the participant. During the first visit, participants performed a familiarization on the isokinetic dynamometer, which consisted of 10 concentric knee flexion-extensions at 60°/s. At the end of the second trial, participants performed 5 maximum concentric knee flexion-extensions of the dominant leg at 60°/s (Figure 1[C]). Peak torque (PT) for each movement was considered the greatest PT production over the 5 repetitions.
Statistical Analysis Mean ± SD values were calculated for all assessments. Validity of maximal-strength assessments of the knee flexors and extensors using elastic bands was explored by calculating Pearson correlation coefficients between 1-RM of the second trial and concentric PT. As general rule, we considered correlation coefficients >.90 very high, .70 to .89 high, and .50 to .69 moderate.7 Relative reliability of maximal-strength assessments using elastic bands was calculated with the intraclass
correlation coefficient (ICC2,1) between the 2 trials. ICC values were interpreted in the same way as the Pearson correlation coefficients. Absolute reliability was calculated with the coefficient of variation (CV). An analytical goal of
