Scand J Med Sci Sports 2014: ••: ••–•• doi: 10.1111/sms.12187
© 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
Evaluation of elastic bands for lower extremity resistance training in adults with and without musculo-skeletal pain E. Sundstrup1,2, M. D. Jakobsen1,2, C. H. Andersen1, T. Bandholm3, K. Thorborg3,4, M. K. Zebis4, L. L. Andersen1 National Research Centre for the Working Environment, Copenhagen, Denmark, 2Institute for Sports Science and Clinical Biomechanics, University of Southern Denmark, Odense, Denmark, 3Physical Medicine & Rehabilitation Research – Copenhagen (PMR-C), Clinical Research Center, and Departments of Orthopedic Surgery and Physical Therapy, Copenhagen University Hospital, Hvidovre, Denmark, 4Arthroscopic Centre Amager, Amager University Hospital, Copenhagen Denmark Corresponding author: Emil Sundstrup, MSc, National Research Centre for the Working Environment, Lersø Parkalle 105, DK 2100 Copenhagen Ø, Denmark. Tel: +45 26 22 30 45, Fax: +45 39 16 52 01, E-mail: [email protected]
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Accepted for publication 30 December 2013
Therapists commonly use elastic bands in resistance exercises during rehabilitation of smaller muscles, such as in the shoulder. However, the effectiveness has not yet been investigated for larger muscle groups. This study investigates muscle activity during lower extremity exercises. Electromyographic (EMG) activity of 10 muscles was measured in 24 women and 18 men during lunges with elastic resistance, lunges with dumbbells, and unilateral leg press in machine using 10 repetition maximum loadings, and normalized to maximal voluntary isometric contraction EMG. Lunges with dumbbells and leg press showed higher activity than lunges with elastic resistance
for the vasti and rectus femoris (P < 0.01), whereas lunges with elastic resistance showed higher activity of gluteus maximus, hamstrings, and erector spinae (P < 0.01). Gender, age, and pain in the knees and hip did not influence these findings. However, pain in the lower back decreased muscular activity of the gluteus maximus and vastus medialis (P < 0.01). Lunges with elastic resistance induce high levels of muscle activity in all the large muscle groups at the hip, knee, and back. Importantly, the efficiency of these exercises was equally high regardless of gender, age, and pain in the knees and hip, whereas pain in the lower back led to altered activation strategies.
Resistance training has been shown most effective in the prevention and/or rehabilitation of tendinopathy (Kongsgaard et al., 2010), unspecific muscle pain (Andersen et al., 2011), low back pain (Kell & Asmundson, 2009), and anterior cruciate ligament injury (Yack et al., 1993). Resistance training is typically performed using gym equipment, such as free weights or exercise machines (Andersen et al., 2006, 2008). However, elastic resistance bands have gained popularity because of their low cost, simplicity, versatility, and portability. Nevertheless, although elastic resistance effectively strengthens smaller muscles in the neck, shoulder, and arm (Andersen et al., 2010, 2011), their efficacy has yet to be investigated in the larger and stronger muscles in the lower extremities. Synergistic muscle activity of the legs and back are important during normal function and this has shown to be impaired during painful conditions. For instance, patients with low back pain exhibit not only reduced trunk muscle strength but also a deficit in hip extensor and hamstring strength (Lee et al., 1995; Nourbakhsh & Arab, 2002; Elfving et al., 2003; Crossman et al., 2004; Marshall et al., 2010). This, along with the growing number of people with back and knee pain, stresses the need for a simple, cost-effective, and readily available
intervention aimed at normalizing muscle functioning. Thus, exercises targeting these muscle groups, using cheap, readily available equipment, are of great clinical value. Leg extension exercises – such as leg press and lunges – performed at high exercise intensities are widely used during rehabilitation, not only to increase maximal muscle strength and improve postural balance but also for its effect on the clinical outcome (Suetta et al., 2004a, b). However, these exercises might not always be optimal when used in a clinical setting, workplace environment, or as part of a home rehabilitation program. Thus, a need for portable, cheap, and “easy-to-use” alternative such as elastic resistance bands exists. Numerous studies have used electromyography (EMG) to evaluate exercise intensity of rehabilitation and strength training exercises (Andersen et al., 2006, 2008). EMG reflects the summation of action potentials traveling across the muscle and is commonly normalized to EMG obtained during a maximal voluntary contraction. Hereby, it expresses intensity as a percentage of the maximal muscle activity elicited during a standardized and maximal reference contraction, in which the investigated muscle works as a prime mover. This provides an estimate of exercise intensity for specific muscles involved in both simple and complex movements (Ballantyne et al.,
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Sundstrup et al. 1993; Hintermeister et al., 1998; Andersen et al., 2008). Exercise recommendations in rehabilitation are largely based on EMG studies using healthy, pain-free individuals (Andersen et al., 2006). However, because pain may induce altered muscle activity patterns (Graven-Nielsen & Arendt-Nielsen, 2008), proper exercise evaluation for rehabilitation purposes should include individuals with pain. Further, for general exercise recommendations, it is important to determine whether women and men, as well as younger and elderly individuals, will benefit equally from exercises performed with elastic resistance. The aim of our study was to investigate the level of muscle activity during lower extremity exercises with elastic resistance compared with dumbbells and machines. We hypothesized that comparably high level of muscle activity is achievable during lower body resistance exercises with elastic tubing, dumbbells, and machines. Further, we investigated the influence of gender, age, and musculoskeletal pain on muscle activity levels during the respective exercises. Methods Participants The study was performed in Copenhagen, Denmark. A group of 42 untrained adults (24 women and 18 men) were recruited from a large workplace with various job tasks. Eleven subjects reported pain in the lower back, whereas six and seven individuals reported pain in the hip and knees, respectively. Exclusion criteria were blood pressure above 160/100, a diagnosed disc prolapse, or serious chronic disease. Table 1 shows demographics and occurrence of musculo-skeletal pain symptoms. All subjects completed a full test protocol with elastic resistance, dumbbells, and in the training machine. All subjects were informed about the purpose and content of the project and gave written informed consent to participate in the study, which conformed to the Declaration of Helsinki and was approved by the Local Ethical Committee (H-3-2010-062).
trunk extension to induce a maximal EMG response of the tested muscles. Two isometric MVCs were performed for each muscle, and the trial with the highest EMG was used for normalization of the peak EMGs in the resistance exercises. Subjects were instructed to gradually increase muscle contraction force toward maximum over a period of 2 s, sustain the MVC for 3 s, and then slowly release the force again. Strong and standardized verbal encouragement was given during all trials.
Exercise equipment Three different types of exercise equipment were used: (a) elastic 41-in. bands in a closed loop with resistances ranging from light to very heavy (Iron Woody, Olney, Montana, USA); (b) dumbbells (1–40 kg); and (c) a leg press machine with loads ranging from 10 to 200 kg (horizontal seated leg press, Technogym, Gambettola, Italy).
Exercise description A week prior to testing, the participants performed a 10 repetition maximum test (10 RM) for the three exercises. All exercises were performed unilaterally. On the day of EMG measurements, participants warmed up with submaximal loads and then performed three consecutive repetitions with the 10 RM load to avoid the influence of fatigue on the subsequent exercises. All exercises were performed in a slowly controlled manner, i.e., lifting (∼1.5 s) and lowering (∼1.5 s) without sudden jerk or acceleration. The order of exercises was randomized for each subject, and the rest period between exercises was approximately 5 min. The exercises are described below and shown in Fig. 1.
Lunge with elastic resistance (Fig. 1a) The participant was standing upright with one foot in front and the other behind the body. The toes and feet were facing straight ahead. The front foot was placed on one end of the elastic band, whereas the other end of the elastic band was placed over the contralateral shoulder. The participant then lowered the body (eccentric phase) until the back knee reached the floor (∼90° knee joint angle), and then raised the body up to the starting position (concentric phase). The body was maintained in an upright position throughout the exercise.
Maximal voluntary isometric contraction (MVC)
Lunge with dumbbells (Fig. 1b)
Prior to the dynamic exercises described below, isometric MVCs were performed according to standardized procedures during knee extension and flexion, hip abduction, adduction and extension, and
The participant was standing upright with one foot in front and the other behind the body. The toes and feet were facing straight ahead. The participant held a dumbbell in each hand. The participant then lowered the body (eccentric phase) until the back knee reached the floor (∼90° knee joint angle), and then raised the body up to the starting position (concentric phase). The body was maintained in an upright position throughout the exercise.
Table 1. Demographics and pain intensity (worst pain in the lower back, hips, and knees) of the men and women of this study
Men
n Age (years) Height (cm) Weight (kg) BMI Pain intensity (0–10)
Women
Control
Pain
Control
Pain
10 37 (12) 180 (6) 81 (8) 25 (1) 1.5 (1.3)
8 45 (15) 175 (7) 74 (8) 24 (2) 5.4 (1.8)
13 44 (9) 166 (7) 67 (13) 25 (5) 2.2 (1)
11 45 (9) 165 (5) 60 (7) 22 (3) 5.6 (1.4)
Leg press (Fig. 1c) The participant was seated in a Technogym horizontal leg press machine with the leg extended and 45° hip flexion. The participant then bent the leg (i.e., flexion of knee and hip joints) to lower the weight (eccentric phase) to approximately 90° knee joint angle and then extending the leg (concentric phase) to nearly full knee extension.
EMG signal sampling and analysis BMI, body mass index. Values are expressed as mean (SD). Pain cases were defined as those having pain intensity of at least 4 in the lower back or hips and controls as those having a pain intensity of 3 or less in both regions.
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EMG signals were recorded from 10 muscles of the legs, glutes, and back: the mid-portion of the vastus medialis, vastus lateralis, rectus femoris, biceps femoris, semitendinosus, adductor magnus, gluteus medius, gluteus maximus, and the left and right erector
Elastic bands for lower extremity activation (a)
(b)
(c)
Fig. 1. Illustration of the resistance exercises with elastic band (a), dumbbells (b), and in a Technogym machine (c). The exercises are lunges using elastic resistance and dumbbells and unilateral leg press. spinae. A bipolar surface EMG configuration (Blue Sensor N-00-S, Ambu A/S, Ballerup, Denmark) and an interelectrode distance of 2 cm were used. Before affixing the electrodes, the skin of the respective area was prepared with scrubbing gel (Acqua gel, Meditec, Parma, Italy) to effectively lower the impedance to less than 10 kΩ. Electrode placement followed the SENIAM recommendations (SENIAM, 2011). The EMG electrodes were connected directly to wireless probes that preamplified the signal (gain 400) and transmitted data in real time to a nearby 16-channel PC-interface receiver (TeleMyo DTS Telemetry, Noraxon, Arizona, USA). The dimension of the probes was 3.4 cm × 2.4 cm × 3.5 cm. The sampling rate was set to 1500 Hz with a bandwidth of 10–500 Hz to avoid aliasing. The resolution of the signals was 16 bits. The common mode rejection ratio was better than 100 dB. Representative samplings of raw EMG from one of the subjects during each of the three exercises are shown in Fig. 2. During later analysis, all raw EMG signals obtained during MVCs as well as during the exercises were digitally filtered, consisting of (a) high-pass filtering at 10 Hz, and (b) a moving root mean square (RMS) filter of 500 ms. For each individual muscle, peak RMS EMG of the three repetitions performed at each level was determined, and the average value of these three repetitions was then normalized to the maximal RMS EMG (nEMG) obtained during MVC (Andersen et al., 2010; Sundstrup et al., 2012).
Statistics A two-way (3 × 10) repeated analysis of variance (ANOVA) (Proc Mixed, SAS version 9, SAS Institute, Cary, North Carolina, USA) was used to locate the differences between exercises and muscles. Factors included in the model were Exercise (elastic resistance, dumbbells, and machine), Muscle (the 10 muscles), and Exercise × Muscle interaction. The analyses were stratified for contraction mode (eccentric and concentric). We also used gender, age, and pain in the knees, hip, and lower back as dichotomous multiadjusted covariates in this analysis. Normalized EMG was the dependent variable. When a significant main effect was found using a two-way ANOVA, post-hoc t-test was made to locate the differences. Further, in a final analysis, we included Back pain × Muscle interaction to test whether back pain influenced EMG differently in the different muscles. Values are reported as least square means (SE), unless otherwise stated. The critical P-value was set to 0.01 to avoid mass significance.
Covariates We included both men and women, younger and elderly, and individuals with and without musculo-skeletal pain. Age was dichotomized to below and above 50 years of age; participants of less than 50 years were classified as “younger” and participants of 50 years and older were classified as “elderly.” Musculo-skeletal pain intensity was assessed on a 0–10 numerical rating scale for the knees, hip, and low back, where 0 is “no pain” and 10 is “worst imaginable pain.” Subsequently, pain rated on the numerical rating scale was dichotomized into two groupings: “pain” as a score of 4–10 and “no or minor pain” as 0–3. This cut-point was based on a previous study showing more clinically relevant findings at pain intensities of 4 or above (Kaergaard et al., 2000). Eleven subjects reported pain in the lower back, whereas six and seven individuals reported pain in the hip and knees, respectively.
Results Exercise evaluation During both the concentric (F = 6.9, P < 0.0001) and the eccentric (F = 5.6, P < 0.0001) phases of the contraction, a significant Muscle × Exercise interaction existed, i.e., muscle activity of the 10 investigated muscles varied differently across exercises. Table 2 provides nEMG values for the respective muscles and exercises during the concentric and eccentric phases of contraction. When comparing across muscles, nEMG was generally highest in the vasti and glutes (Table 2). However, lunges with dumbbells and leg press showed higher activity of the vasti and rectus femoris than lunges with elastic resistance (Table 2). By contrast, lunges with elastic resistance showed higher activity of erector spinae and hamstrings than lunges with dumbbells and leg press (Table 2).
Influence of gender, age, and musculo-skeletal pain There was a significant interaction between muscles and pain in the lower back during both the concentric phase
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Sundstrup et al.
Fig. 2. Normalized electromyography (nEMG) signals during three repetitions of lunges with elastic band (left), lunges with dumbbells (middle), and unilateral leg press (right) in the vastus lateralis, biceps femoris, gluteus maximus, and erector spinae muscles. The root mean square EMG recording is overlaid (pink tracing) on the raw EMG normalized to maximal voluntary isometric contraction EMG.
(F = 4.0, P < 0.0001) and the eccentric phase (F = 6.2, P < 0.0001). The post-hoc test revealed that individuals with low back pain demonstrated significantly lower nEMG in gluteus maximus (P < 0.01) and vastus medialis (P < 0.0001) than individuals without low back pain (Table 3). However, pain in the hip and knees did not significantly influence the muscle activation level (i.e.,
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nEMG) in any of the evaluated muscles (F = 0.0–1.2, P = 0.2–0.9). There were no significant main effects of gender and age on nEMG during the concentric and eccentric phases of contraction (F = 0.0–0.2, P = 0.36–0.92). For women and men, respectively, nEMG averaged for all muscles was 56 (2.7)% and 54 (3.5)% (n.s.) during the concentric
Elastic bands for lower extremity activation Table 2. Normalized peak electromyography (EMG) of 10 selected muscles during the concentric (Con) and eccentric (Ecc) phase of the three resistance exercises
Elastic
Vastus medialis Vastus lateralis Rectus femoris Gluteus medius Gluteus maximus Erector spinae (left) Erector spinae (right) Biceps femoris Semitendinosus Adductor
Dumbbell
Machine
Con
Ecc
Con
Ecc
Con
Ecc
83 (5.5) 80 (5.5) 51 (5.5) 66 (5.5) 63 (5.5)D 57 (5.5)DD,MMM 58 (5.5)D,MMM 50 (5.5)DDD 38 (5.5)DD 36 (5.5)
77 (4.7) 71 (4.6) 46 (4.7) 45 (4.6) 42 (4.7) 41 (4.6)MMM 43 (4.6)MMM 38 (4.6)D,M 28 (4.6) 35 (4.6)
94 (5.6) 85 (5.7) 61 (5.6) 56 (5.7) 48 (5.6) 37 (5.6)M 41 (5.5)M 29 (5.5) 19 (5.5) 40 (5.6)
93 (4.7)EE 84 (4.8)E 62 (4.7)EE 46 (4.8) 38 (4.7) 32 (4.7)MM 36 (4.7)MMM 23 (4.7) 16 (4.6) 41 (4.7)M
99 (5.5)E 93 (5.6) 66 (5.5)E 61 (5.5) 51 (5.6) 21 (5.5) 25 (5.6) 36 (5.5) 25 (5.5) 35 (5.5)
87 (4.7) 79 (4.7) 56 (4.7) 36 (4.7) 31 (4.7) 16 (4.6) 16 (4.7) 26 (4.6) 16 (4.6) 29 (4.7)
Values are presented as mean ± SE. E(P < 0.01), EE(P < 0.001), EEE(P < 0.0001) denote significantly different from Elastic; D(P < 0.01), DD(P < 0.001), DDD (P < 0.0001) denote significantly different from Dumbbell; M(P < 0.01), MM(P < 0.001), MMM(P < 0.0001) denote significantly different from Machine. All P-values are from the post-hoc test. Table 3. Normalized concentric peak electromyography (EMG) of 10 selected muscles during an average of all three exercises for individuals with and without pain in the lower back
n Vastus medialis Vastus lateralis Gluteus medius Gluteus maximus Erector spinae (left) Erector spinae (right) Rectus femoris Biceps femoris Semitendinosus Adductor
No pain in the lower back
Pain in the lower back
31 109 (5.0)** 91 (5.0) 64 (5.0) 63 (5.0)* 44 (4.9) 44 (4.9) 65 (5.0) 43 (4.9) 32 (4.9) 35 (5.0)
11 74 (6.4) 80 (6.5) 58 (6.5) 44 (6.4) 33 (6.5) 39 (6.5) 54 (6.4) 34 (6.4) 23 (6.4) 38 (6.4)
Values are presented as mean ± SE and significant between-group differences are marked with * (P < 0.01) and ** (P < 0.0001). All P-values are from the post-hoc test.
phase and 47 (2.2)% and 45 (2.8)% (n.s.) during the eccentric phase. For younger and elderly individuals, respectively, nEMG averaged for all muscles was 54 (2.3)% and 56 (3.9)% (n.s.) during the concentric phase and 45 (1.9)% and 46 (3.2)% (n.s.) during the eccentric phase. Discussion The study found that elastic resistance induced comparable high levels of muscle activity as seen in traditional exercises using dumbbells or machines as resistance. Importantly, the efficiency of these exercises was equally high regardless of gender, age, and pain intensity in the knees and hip. However, pain in the lower back compromised the activation level of gluteus maximus and vastus medialis for all exercises. Some biomechanical differences in the execution of the exercises clearly existed, which could add to the interpretation of the results (Fig. 1). Lunges performed with
elastic resistance were executed with the spine in a neutral position, which was not the case when it was performed with dumbbells. Good alignment of the three curves of the spine will minimize inappropriate shear forces and long lever arms, which initially can be a problem for low back pain patients. The results of the present study showed that lunges with elastic resistance were more posterior kinetic chain-dominant (i.e., predominantly activating the muscles on the posterior of the body), inducing higher levels of hamstring and erector spinae activity compared with dumbbells and machines. Biomechanically, the anterior pull of the elastic band on the upper body – caused by the horizontal distance from the front foot where one end of the band is attached to the contralateral shoulder where the other end of the band is attached – causes an external hip flexor moment, which must be counteracted by an internal hip extensor moment (Fig. 1). This could lead to increased gluteus and hamstring muscle activity. Further, to maintain an upright position throughout the exercise, a high level of spinal extension and stabilizing muscle activity is needed. This likely explains the high levels of erector spinae EMG during the lunge with elastic band compared with the two other exercises. Further, lunges with elastic resistance may demand a greater extend of balance assessment and postural control compared with lunges performed with dumbbells where the weights acts as balance bars. Compensatory muscle activity in the hamstrings and erector spinae may be necessary to preserve postural stability during movement. EMG activity of at least 60% of MVC is recommended to acquire the desired physiological adaptations in terms of efficient strength gain, neural adaptations, and muscle fiber hypertrophy (Arokoski et al., 1999; American College of Sports Medicine, 2009). Hence, in our study, lunges with elastic resistance induced sufficient activation of the gluteal musculature (66% max nEMG) and quadriceps (>80% max nEMG) to positively affect this muscle group in both healthy people and individuals with musculo-skeletal pain. However, quadriceps activity was
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Sundstrup et al. higher during lunges with free weights and in machine, favoring these training modalities for quadriceps stimulation. In accordance, lower eccentric quadriceps EMG muscle activity has been observed during knee extensions performed with elastic tubing compared with knee extensions using an isotonic training machine (Jakobsen et al., 2012). However, in that study, no difference in quadriceps EMG was observed during the concentric contraction phase. Even though, elastic resistance should be considered by the physician as an effective quadriceps exercise initially in a rehabilitation program and as an easy-to-use alternative in situations with limited access to traditional training equipment. Individuals with pain in the lower back revealed a different muscle activation pattern during all three exercises, i.e., lower gluteus maximus and vastus medialis activation, than those without pain. In line with this, Leinonen et al. (2000) observed a reduced gluteus maximus activation phase during trunk flexion and that the activation of this specific muscle ended earlier during trunk extension in low back pain patients compared with healthy controls (Leinonen et al., 2000). On the contrary, Arab et al. (2011) found no statistical difference in gluteus maximus activation during prone hip extension in subjects with and without low back pain. Our study supports the idea of different gluteus maximus activation strategies in persons with low back pain, probably compromising stability of the lumbar area. Strengthening exercises targeting the gluteus maximus could counteract this activation deficit or deconditioning and should be considered for individuals with low back pain. To our knowledge, no studies have reported reduced vastus medialis activation in persons with low back pain. It could be speculated that the compromised gluteal musculature activity leads to inward rotation of the femur and thus valgus position of the knees, causing decreased stress across the medial compartment and medial structures of the knee. Importantly from a clinical perspective, individuals with pain in their knees and hip (at least 4 on a 0–10 scale) activated their muscles to a similar extent as those without pain (3 or less on a scale of 0–10). In this study, it is indicated that the present exercises are effective for healthy individuals as well as patients with pain in the specific regions.
joint torque curves mimic that of free weights and machines. This study compared the relative level of muscle activity across the three exercises, and strength was not measured. Thus, the adaptive effects on muscle strength cannot be extrapolated from these results, and a randomized controlled trial would be necessary to draw such conclusions. Analyzing the influence of gender, age, and pain on the level of muscle activity strengthens the generalizability of our findings. However, the study population included working aged adults only, which limits the reported lack of an age effect to this relative narrow age range. Learning the exercise technique and performing repetition maximum tests to determine the appropriate load a week prior to testing minimizes fatigue on the actual day of testing. Further, randomizing the order of exercises eliminates any potential influence on muscle activity from one exercise to another. In conclusion, lunges with elastic resistance induced equally high levels of muscle activity compared with lunge with dumbbells and unilateral leg press in machine. Lunge with elastic resistance induced high levels of muscle activity in all the large muscle groups at the hip, knee, and back. Importantly, pain in the lower back resulted in a changed muscle activation pattern in all three exercises, whereas women and men, younger and elderly, and individuals with pain in the knees and hip benefited equally from the exercise. Lunge with elastic resistance therefore seems to be a feasible and simple alternative to traditional resistance exercises for activation of trunk and leg muscles. Perspectives Several studies have described the efficiency of elastic resistance exercises for the smaller muscles in the neck, shoulder, and arm (Andersen et al., 2010, 2011) whereas the effect and feasibility for larger muscle groups are questionable. Our study provides evidence that lunges with elastic resistance activate and stimulate a variety of larger muscle groups, making it a good single exercise choice for knee, hip, and back strengthening and stabilization. Further, lunges performed with elastic resistance is a practical, portable, and easy-to-use alternative to traditional training exercises, ideal for home-based rehabilitation or rehabilitation in clinics with no traditional strength training machines.
Limitations and strengths of the study When describing the differences and similarities in muscle activity between exercises performed with elastic resistance, dumbbells, and machines, the properties of the equipment used should be taken into account. Whereas dumbbells and machines provide isotonic resistance, elastic resistance increases linearly with the elongation. More research on multi-joint lower extremity exercises using elastic resistance is needed to clarify whether the
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Key words: Electromyography, resistance training, elastic band, free weights
Acknowledgements L. L. A. received a grant from the Danish Working Environment Research Fund (Grant No. 48–2010-03) for this study. Warm thanks are due to the students from the Metropolitan University College for practical help during the project.
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© 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
Evaluation of elastic bands for lower extremity resistance training in adults with and without musculo-skeletal pain E. Sundstrup1,2, M. D. Jakobsen1,2, C. H. Andersen1, T. Bandholm3, K. Thorborg3,4, M. K. Zebis4, L. L. Andersen1 National Research Centre for the Working Environment, Copenhagen, Denmark, 2Institute for Sports Science and Clinical Biomechanics, University of Southern Denmark, Odense, Denmark, 3Physical Medicine & Rehabilitation Research – Copenhagen (PMR-C), Clinical Research Center, and Departments of Orthopedic Surgery and Physical Therapy, Copenhagen University Hospital, Hvidovre, Denmark, 4Arthroscopic Centre Amager, Amager University Hospital, Copenhagen Denmark Corresponding author: Emil Sundstrup, MSc, National Research Centre for the Working Environment, Lersø Parkalle 105, DK 2100 Copenhagen Ø, Denmark. Tel: +45 26 22 30 45, Fax: +45 39 16 52 01, E-mail: [email protected]
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Accepted for publication 30 December 2013
Therapists commonly use elastic bands in resistance exercises during rehabilitation of smaller muscles, such as in the shoulder. However, the effectiveness has not yet been investigated for larger muscle groups. This study investigates muscle activity during lower extremity exercises. Electromyographic (EMG) activity of 10 muscles was measured in 24 women and 18 men during lunges with elastic resistance, lunges with dumbbells, and unilateral leg press in machine using 10 repetition maximum loadings, and normalized to maximal voluntary isometric contraction EMG. Lunges with dumbbells and leg press showed higher activity than lunges with elastic resistance
for the vasti and rectus femoris (P < 0.01), whereas lunges with elastic resistance showed higher activity of gluteus maximus, hamstrings, and erector spinae (P < 0.01). Gender, age, and pain in the knees and hip did not influence these findings. However, pain in the lower back decreased muscular activity of the gluteus maximus and vastus medialis (P < 0.01). Lunges with elastic resistance induce high levels of muscle activity in all the large muscle groups at the hip, knee, and back. Importantly, the efficiency of these exercises was equally high regardless of gender, age, and pain in the knees and hip, whereas pain in the lower back led to altered activation strategies.
Resistance training has been shown most effective in the prevention and/or rehabilitation of tendinopathy (Kongsgaard et al., 2010), unspecific muscle pain (Andersen et al., 2011), low back pain (Kell & Asmundson, 2009), and anterior cruciate ligament injury (Yack et al., 1993). Resistance training is typically performed using gym equipment, such as free weights or exercise machines (Andersen et al., 2006, 2008). However, elastic resistance bands have gained popularity because of their low cost, simplicity, versatility, and portability. Nevertheless, although elastic resistance effectively strengthens smaller muscles in the neck, shoulder, and arm (Andersen et al., 2010, 2011), their efficacy has yet to be investigated in the larger and stronger muscles in the lower extremities. Synergistic muscle activity of the legs and back are important during normal function and this has shown to be impaired during painful conditions. For instance, patients with low back pain exhibit not only reduced trunk muscle strength but also a deficit in hip extensor and hamstring strength (Lee et al., 1995; Nourbakhsh & Arab, 2002; Elfving et al., 2003; Crossman et al., 2004; Marshall et al., 2010). This, along with the growing number of people with back and knee pain, stresses the need for a simple, cost-effective, and readily available
intervention aimed at normalizing muscle functioning. Thus, exercises targeting these muscle groups, using cheap, readily available equipment, are of great clinical value. Leg extension exercises – such as leg press and lunges – performed at high exercise intensities are widely used during rehabilitation, not only to increase maximal muscle strength and improve postural balance but also for its effect on the clinical outcome (Suetta et al., 2004a, b). However, these exercises might not always be optimal when used in a clinical setting, workplace environment, or as part of a home rehabilitation program. Thus, a need for portable, cheap, and “easy-to-use” alternative such as elastic resistance bands exists. Numerous studies have used electromyography (EMG) to evaluate exercise intensity of rehabilitation and strength training exercises (Andersen et al., 2006, 2008). EMG reflects the summation of action potentials traveling across the muscle and is commonly normalized to EMG obtained during a maximal voluntary contraction. Hereby, it expresses intensity as a percentage of the maximal muscle activity elicited during a standardized and maximal reference contraction, in which the investigated muscle works as a prime mover. This provides an estimate of exercise intensity for specific muscles involved in both simple and complex movements (Ballantyne et al.,
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Sundstrup et al. 1993; Hintermeister et al., 1998; Andersen et al., 2008). Exercise recommendations in rehabilitation are largely based on EMG studies using healthy, pain-free individuals (Andersen et al., 2006). However, because pain may induce altered muscle activity patterns (Graven-Nielsen & Arendt-Nielsen, 2008), proper exercise evaluation for rehabilitation purposes should include individuals with pain. Further, for general exercise recommendations, it is important to determine whether women and men, as well as younger and elderly individuals, will benefit equally from exercises performed with elastic resistance. The aim of our study was to investigate the level of muscle activity during lower extremity exercises with elastic resistance compared with dumbbells and machines. We hypothesized that comparably high level of muscle activity is achievable during lower body resistance exercises with elastic tubing, dumbbells, and machines. Further, we investigated the influence of gender, age, and musculoskeletal pain on muscle activity levels during the respective exercises. Methods Participants The study was performed in Copenhagen, Denmark. A group of 42 untrained adults (24 women and 18 men) were recruited from a large workplace with various job tasks. Eleven subjects reported pain in the lower back, whereas six and seven individuals reported pain in the hip and knees, respectively. Exclusion criteria were blood pressure above 160/100, a diagnosed disc prolapse, or serious chronic disease. Table 1 shows demographics and occurrence of musculo-skeletal pain symptoms. All subjects completed a full test protocol with elastic resistance, dumbbells, and in the training machine. All subjects were informed about the purpose and content of the project and gave written informed consent to participate in the study, which conformed to the Declaration of Helsinki and was approved by the Local Ethical Committee (H-3-2010-062).
trunk extension to induce a maximal EMG response of the tested muscles. Two isometric MVCs were performed for each muscle, and the trial with the highest EMG was used for normalization of the peak EMGs in the resistance exercises. Subjects were instructed to gradually increase muscle contraction force toward maximum over a period of 2 s, sustain the MVC for 3 s, and then slowly release the force again. Strong and standardized verbal encouragement was given during all trials.
Exercise equipment Three different types of exercise equipment were used: (a) elastic 41-in. bands in a closed loop with resistances ranging from light to very heavy (Iron Woody, Olney, Montana, USA); (b) dumbbells (1–40 kg); and (c) a leg press machine with loads ranging from 10 to 200 kg (horizontal seated leg press, Technogym, Gambettola, Italy).
Exercise description A week prior to testing, the participants performed a 10 repetition maximum test (10 RM) for the three exercises. All exercises were performed unilaterally. On the day of EMG measurements, participants warmed up with submaximal loads and then performed three consecutive repetitions with the 10 RM load to avoid the influence of fatigue on the subsequent exercises. All exercises were performed in a slowly controlled manner, i.e., lifting (∼1.5 s) and lowering (∼1.5 s) without sudden jerk or acceleration. The order of exercises was randomized for each subject, and the rest period between exercises was approximately 5 min. The exercises are described below and shown in Fig. 1.
Lunge with elastic resistance (Fig. 1a) The participant was standing upright with one foot in front and the other behind the body. The toes and feet were facing straight ahead. The front foot was placed on one end of the elastic band, whereas the other end of the elastic band was placed over the contralateral shoulder. The participant then lowered the body (eccentric phase) until the back knee reached the floor (∼90° knee joint angle), and then raised the body up to the starting position (concentric phase). The body was maintained in an upright position throughout the exercise.
Maximal voluntary isometric contraction (MVC)
Lunge with dumbbells (Fig. 1b)
Prior to the dynamic exercises described below, isometric MVCs were performed according to standardized procedures during knee extension and flexion, hip abduction, adduction and extension, and
The participant was standing upright with one foot in front and the other behind the body. The toes and feet were facing straight ahead. The participant held a dumbbell in each hand. The participant then lowered the body (eccentric phase) until the back knee reached the floor (∼90° knee joint angle), and then raised the body up to the starting position (concentric phase). The body was maintained in an upright position throughout the exercise.
Table 1. Demographics and pain intensity (worst pain in the lower back, hips, and knees) of the men and women of this study
Men
n Age (years) Height (cm) Weight (kg) BMI Pain intensity (0–10)
Women
Control
Pain
Control
Pain
10 37 (12) 180 (6) 81 (8) 25 (1) 1.5 (1.3)
8 45 (15) 175 (7) 74 (8) 24 (2) 5.4 (1.8)
13 44 (9) 166 (7) 67 (13) 25 (5) 2.2 (1)
11 45 (9) 165 (5) 60 (7) 22 (3) 5.6 (1.4)
Leg press (Fig. 1c) The participant was seated in a Technogym horizontal leg press machine with the leg extended and 45° hip flexion. The participant then bent the leg (i.e., flexion of knee and hip joints) to lower the weight (eccentric phase) to approximately 90° knee joint angle and then extending the leg (concentric phase) to nearly full knee extension.
EMG signal sampling and analysis BMI, body mass index. Values are expressed as mean (SD). Pain cases were defined as those having pain intensity of at least 4 in the lower back or hips and controls as those having a pain intensity of 3 or less in both regions.
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EMG signals were recorded from 10 muscles of the legs, glutes, and back: the mid-portion of the vastus medialis, vastus lateralis, rectus femoris, biceps femoris, semitendinosus, adductor magnus, gluteus medius, gluteus maximus, and the left and right erector
Elastic bands for lower extremity activation (a)
(b)
(c)
Fig. 1. Illustration of the resistance exercises with elastic band (a), dumbbells (b), and in a Technogym machine (c). The exercises are lunges using elastic resistance and dumbbells and unilateral leg press. spinae. A bipolar surface EMG configuration (Blue Sensor N-00-S, Ambu A/S, Ballerup, Denmark) and an interelectrode distance of 2 cm were used. Before affixing the electrodes, the skin of the respective area was prepared with scrubbing gel (Acqua gel, Meditec, Parma, Italy) to effectively lower the impedance to less than 10 kΩ. Electrode placement followed the SENIAM recommendations (SENIAM, 2011). The EMG electrodes were connected directly to wireless probes that preamplified the signal (gain 400) and transmitted data in real time to a nearby 16-channel PC-interface receiver (TeleMyo DTS Telemetry, Noraxon, Arizona, USA). The dimension of the probes was 3.4 cm × 2.4 cm × 3.5 cm. The sampling rate was set to 1500 Hz with a bandwidth of 10–500 Hz to avoid aliasing. The resolution of the signals was 16 bits. The common mode rejection ratio was better than 100 dB. Representative samplings of raw EMG from one of the subjects during each of the three exercises are shown in Fig. 2. During later analysis, all raw EMG signals obtained during MVCs as well as during the exercises were digitally filtered, consisting of (a) high-pass filtering at 10 Hz, and (b) a moving root mean square (RMS) filter of 500 ms. For each individual muscle, peak RMS EMG of the three repetitions performed at each level was determined, and the average value of these three repetitions was then normalized to the maximal RMS EMG (nEMG) obtained during MVC (Andersen et al., 2010; Sundstrup et al., 2012).
Statistics A two-way (3 × 10) repeated analysis of variance (ANOVA) (Proc Mixed, SAS version 9, SAS Institute, Cary, North Carolina, USA) was used to locate the differences between exercises and muscles. Factors included in the model were Exercise (elastic resistance, dumbbells, and machine), Muscle (the 10 muscles), and Exercise × Muscle interaction. The analyses were stratified for contraction mode (eccentric and concentric). We also used gender, age, and pain in the knees, hip, and lower back as dichotomous multiadjusted covariates in this analysis. Normalized EMG was the dependent variable. When a significant main effect was found using a two-way ANOVA, post-hoc t-test was made to locate the differences. Further, in a final analysis, we included Back pain × Muscle interaction to test whether back pain influenced EMG differently in the different muscles. Values are reported as least square means (SE), unless otherwise stated. The critical P-value was set to 0.01 to avoid mass significance.
Covariates We included both men and women, younger and elderly, and individuals with and without musculo-skeletal pain. Age was dichotomized to below and above 50 years of age; participants of less than 50 years were classified as “younger” and participants of 50 years and older were classified as “elderly.” Musculo-skeletal pain intensity was assessed on a 0–10 numerical rating scale for the knees, hip, and low back, where 0 is “no pain” and 10 is “worst imaginable pain.” Subsequently, pain rated on the numerical rating scale was dichotomized into two groupings: “pain” as a score of 4–10 and “no or minor pain” as 0–3. This cut-point was based on a previous study showing more clinically relevant findings at pain intensities of 4 or above (Kaergaard et al., 2000). Eleven subjects reported pain in the lower back, whereas six and seven individuals reported pain in the hip and knees, respectively.
Results Exercise evaluation During both the concentric (F = 6.9, P < 0.0001) and the eccentric (F = 5.6, P < 0.0001) phases of the contraction, a significant Muscle × Exercise interaction existed, i.e., muscle activity of the 10 investigated muscles varied differently across exercises. Table 2 provides nEMG values for the respective muscles and exercises during the concentric and eccentric phases of contraction. When comparing across muscles, nEMG was generally highest in the vasti and glutes (Table 2). However, lunges with dumbbells and leg press showed higher activity of the vasti and rectus femoris than lunges with elastic resistance (Table 2). By contrast, lunges with elastic resistance showed higher activity of erector spinae and hamstrings than lunges with dumbbells and leg press (Table 2).
Influence of gender, age, and musculo-skeletal pain There was a significant interaction between muscles and pain in the lower back during both the concentric phase
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Sundstrup et al.
Fig. 2. Normalized electromyography (nEMG) signals during three repetitions of lunges with elastic band (left), lunges with dumbbells (middle), and unilateral leg press (right) in the vastus lateralis, biceps femoris, gluteus maximus, and erector spinae muscles. The root mean square EMG recording is overlaid (pink tracing) on the raw EMG normalized to maximal voluntary isometric contraction EMG.
(F = 4.0, P < 0.0001) and the eccentric phase (F = 6.2, P < 0.0001). The post-hoc test revealed that individuals with low back pain demonstrated significantly lower nEMG in gluteus maximus (P < 0.01) and vastus medialis (P < 0.0001) than individuals without low back pain (Table 3). However, pain in the hip and knees did not significantly influence the muscle activation level (i.e.,
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nEMG) in any of the evaluated muscles (F = 0.0–1.2, P = 0.2–0.9). There were no significant main effects of gender and age on nEMG during the concentric and eccentric phases of contraction (F = 0.0–0.2, P = 0.36–0.92). For women and men, respectively, nEMG averaged for all muscles was 56 (2.7)% and 54 (3.5)% (n.s.) during the concentric
Elastic bands for lower extremity activation Table 2. Normalized peak electromyography (EMG) of 10 selected muscles during the concentric (Con) and eccentric (Ecc) phase of the three resistance exercises
Elastic
Vastus medialis Vastus lateralis Rectus femoris Gluteus medius Gluteus maximus Erector spinae (left) Erector spinae (right) Biceps femoris Semitendinosus Adductor
Dumbbell
Machine
Con
Ecc
Con
Ecc
Con
Ecc
83 (5.5) 80 (5.5) 51 (5.5) 66 (5.5) 63 (5.5)D 57 (5.5)DD,MMM 58 (5.5)D,MMM 50 (5.5)DDD 38 (5.5)DD 36 (5.5)
77 (4.7) 71 (4.6) 46 (4.7) 45 (4.6) 42 (4.7) 41 (4.6)MMM 43 (4.6)MMM 38 (4.6)D,M 28 (4.6) 35 (4.6)
94 (5.6) 85 (5.7) 61 (5.6) 56 (5.7) 48 (5.6) 37 (5.6)M 41 (5.5)M 29 (5.5) 19 (5.5) 40 (5.6)
93 (4.7)EE 84 (4.8)E 62 (4.7)EE 46 (4.8) 38 (4.7) 32 (4.7)MM 36 (4.7)MMM 23 (4.7) 16 (4.6) 41 (4.7)M
99 (5.5)E 93 (5.6) 66 (5.5)E 61 (5.5) 51 (5.6) 21 (5.5) 25 (5.6) 36 (5.5) 25 (5.5) 35 (5.5)
87 (4.7) 79 (4.7) 56 (4.7) 36 (4.7) 31 (4.7) 16 (4.6) 16 (4.7) 26 (4.6) 16 (4.6) 29 (4.7)
Values are presented as mean ± SE. E(P < 0.01), EE(P < 0.001), EEE(P < 0.0001) denote significantly different from Elastic; D(P < 0.01), DD(P < 0.001), DDD (P < 0.0001) denote significantly different from Dumbbell; M(P < 0.01), MM(P < 0.001), MMM(P < 0.0001) denote significantly different from Machine. All P-values are from the post-hoc test. Table 3. Normalized concentric peak electromyography (EMG) of 10 selected muscles during an average of all three exercises for individuals with and without pain in the lower back
n Vastus medialis Vastus lateralis Gluteus medius Gluteus maximus Erector spinae (left) Erector spinae (right) Rectus femoris Biceps femoris Semitendinosus Adductor
No pain in the lower back
Pain in the lower back
31 109 (5.0)** 91 (5.0) 64 (5.0) 63 (5.0)* 44 (4.9) 44 (4.9) 65 (5.0) 43 (4.9) 32 (4.9) 35 (5.0)
11 74 (6.4) 80 (6.5) 58 (6.5) 44 (6.4) 33 (6.5) 39 (6.5) 54 (6.4) 34 (6.4) 23 (6.4) 38 (6.4)
Values are presented as mean ± SE and significant between-group differences are marked with * (P < 0.01) and ** (P < 0.0001). All P-values are from the post-hoc test.
phase and 47 (2.2)% and 45 (2.8)% (n.s.) during the eccentric phase. For younger and elderly individuals, respectively, nEMG averaged for all muscles was 54 (2.3)% and 56 (3.9)% (n.s.) during the concentric phase and 45 (1.9)% and 46 (3.2)% (n.s.) during the eccentric phase. Discussion The study found that elastic resistance induced comparable high levels of muscle activity as seen in traditional exercises using dumbbells or machines as resistance. Importantly, the efficiency of these exercises was equally high regardless of gender, age, and pain intensity in the knees and hip. However, pain in the lower back compromised the activation level of gluteus maximus and vastus medialis for all exercises. Some biomechanical differences in the execution of the exercises clearly existed, which could add to the interpretation of the results (Fig. 1). Lunges performed with
elastic resistance were executed with the spine in a neutral position, which was not the case when it was performed with dumbbells. Good alignment of the three curves of the spine will minimize inappropriate shear forces and long lever arms, which initially can be a problem for low back pain patients. The results of the present study showed that lunges with elastic resistance were more posterior kinetic chain-dominant (i.e., predominantly activating the muscles on the posterior of the body), inducing higher levels of hamstring and erector spinae activity compared with dumbbells and machines. Biomechanically, the anterior pull of the elastic band on the upper body – caused by the horizontal distance from the front foot where one end of the band is attached to the contralateral shoulder where the other end of the band is attached – causes an external hip flexor moment, which must be counteracted by an internal hip extensor moment (Fig. 1). This could lead to increased gluteus and hamstring muscle activity. Further, to maintain an upright position throughout the exercise, a high level of spinal extension and stabilizing muscle activity is needed. This likely explains the high levels of erector spinae EMG during the lunge with elastic band compared with the two other exercises. Further, lunges with elastic resistance may demand a greater extend of balance assessment and postural control compared with lunges performed with dumbbells where the weights acts as balance bars. Compensatory muscle activity in the hamstrings and erector spinae may be necessary to preserve postural stability during movement. EMG activity of at least 60% of MVC is recommended to acquire the desired physiological adaptations in terms of efficient strength gain, neural adaptations, and muscle fiber hypertrophy (Arokoski et al., 1999; American College of Sports Medicine, 2009). Hence, in our study, lunges with elastic resistance induced sufficient activation of the gluteal musculature (66% max nEMG) and quadriceps (>80% max nEMG) to positively affect this muscle group in both healthy people and individuals with musculo-skeletal pain. However, quadriceps activity was
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Sundstrup et al. higher during lunges with free weights and in machine, favoring these training modalities for quadriceps stimulation. In accordance, lower eccentric quadriceps EMG muscle activity has been observed during knee extensions performed with elastic tubing compared with knee extensions using an isotonic training machine (Jakobsen et al., 2012). However, in that study, no difference in quadriceps EMG was observed during the concentric contraction phase. Even though, elastic resistance should be considered by the physician as an effective quadriceps exercise initially in a rehabilitation program and as an easy-to-use alternative in situations with limited access to traditional training equipment. Individuals with pain in the lower back revealed a different muscle activation pattern during all three exercises, i.e., lower gluteus maximus and vastus medialis activation, than those without pain. In line with this, Leinonen et al. (2000) observed a reduced gluteus maximus activation phase during trunk flexion and that the activation of this specific muscle ended earlier during trunk extension in low back pain patients compared with healthy controls (Leinonen et al., 2000). On the contrary, Arab et al. (2011) found no statistical difference in gluteus maximus activation during prone hip extension in subjects with and without low back pain. Our study supports the idea of different gluteus maximus activation strategies in persons with low back pain, probably compromising stability of the lumbar area. Strengthening exercises targeting the gluteus maximus could counteract this activation deficit or deconditioning and should be considered for individuals with low back pain. To our knowledge, no studies have reported reduced vastus medialis activation in persons with low back pain. It could be speculated that the compromised gluteal musculature activity leads to inward rotation of the femur and thus valgus position of the knees, causing decreased stress across the medial compartment and medial structures of the knee. Importantly from a clinical perspective, individuals with pain in their knees and hip (at least 4 on a 0–10 scale) activated their muscles to a similar extent as those without pain (3 or less on a scale of 0–10). In this study, it is indicated that the present exercises are effective for healthy individuals as well as patients with pain in the specific regions.
joint torque curves mimic that of free weights and machines. This study compared the relative level of muscle activity across the three exercises, and strength was not measured. Thus, the adaptive effects on muscle strength cannot be extrapolated from these results, and a randomized controlled trial would be necessary to draw such conclusions. Analyzing the influence of gender, age, and pain on the level of muscle activity strengthens the generalizability of our findings. However, the study population included working aged adults only, which limits the reported lack of an age effect to this relative narrow age range. Learning the exercise technique and performing repetition maximum tests to determine the appropriate load a week prior to testing minimizes fatigue on the actual day of testing. Further, randomizing the order of exercises eliminates any potential influence on muscle activity from one exercise to another. In conclusion, lunges with elastic resistance induced equally high levels of muscle activity compared with lunge with dumbbells and unilateral leg press in machine. Lunge with elastic resistance induced high levels of muscle activity in all the large muscle groups at the hip, knee, and back. Importantly, pain in the lower back resulted in a changed muscle activation pattern in all three exercises, whereas women and men, younger and elderly, and individuals with pain in the knees and hip benefited equally from the exercise. Lunge with elastic resistance therefore seems to be a feasible and simple alternative to traditional resistance exercises for activation of trunk and leg muscles. Perspectives Several studies have described the efficiency of elastic resistance exercises for the smaller muscles in the neck, shoulder, and arm (Andersen et al., 2010, 2011) whereas the effect and feasibility for larger muscle groups are questionable. Our study provides evidence that lunges with elastic resistance activate and stimulate a variety of larger muscle groups, making it a good single exercise choice for knee, hip, and back strengthening and stabilization. Further, lunges performed with elastic resistance is a practical, portable, and easy-to-use alternative to traditional training exercises, ideal for home-based rehabilitation or rehabilitation in clinics with no traditional strength training machines.
Limitations and strengths of the study When describing the differences and similarities in muscle activity between exercises performed with elastic resistance, dumbbells, and machines, the properties of the equipment used should be taken into account. Whereas dumbbells and machines provide isotonic resistance, elastic resistance increases linearly with the elongation. More research on multi-joint lower extremity exercises using elastic resistance is needed to clarify whether the
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Key words: Electromyography, resistance training, elastic band, free weights
Acknowledgements L. L. A. received a grant from the Danish Working Environment Research Fund (Grant No. 48–2010-03) for this study. Warm thanks are due to the students from the Metropolitan University College for practical help during the project.
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