|Year : 2014 | Volume
| Issue : 1 | Page : 20-24
Examination of muscle activity with an elastic hamstring assistance device
David Bellar1, Nina LeBlanc1, Lawrence W Judge2
1 School of Kinesiology, University of Louisiana at Lafayette, Lafayette, Louisiana, USA
2 School of Physical Education, Sport and Exercise, Science Ball State University, Muncie, Indiana, USA
|Date of Web Publication||21-Oct-2014|
School of Kinesiology, University of Louisiana at Lafayette, 225 Cajundome Blvd, Lafayette - 70508, Louisiana
Source of Support: None, Conflict of Interest: None
Background: Hamstring injuries are common among athletes and recreationally active people. The goal of the study was to determine if the Hamstrong device was effective in reducing the activity of the hamstring muscles during isometric knee exercise. Materials and Methods: Electrodes were placed on the biceps femoris and semitendinosus in a bipolar configuration on the left leg of all the subjects (N = 12) in order to monitor muscle activity during the experimental procedure. The test involved isometrically holding 15%, 30%, 45%, and 60% of the participant's pre-determined maximum isometric force at 90° and 135° knee extension with and without the Hamstring apparatus. The raw electromyography (EMG) signal was low-pass filtered and amplified prior to being interpreted. Results: There was a significant difference in the signal from the biceps femoris determined via surface electromyography (sEMG) at 90 degrees of knee extension using 30% of peak isometric force as the load (P = 0.043). Additionally in the biceps femoris there were differences in the sEMG signal at 135 degrees of knee extension using 15% (P = 0.0492) and 30% (P = 0.0358) of peak isometric force. In the semitendinosus muscle, there was a significant difference in sEMG signal at 15° of knee extension with 60% of peak isometric force (P = 0.0025). Overall, clinical inferences revealed that the device could be considered 71.4% beneficial or substantially positive to 10.9% for reducing the EMG signal associated with isometric exercise in the biceps femoris (biceps femoris mean: With device 0.319 mV ± 0.13 and without device 0.361 mV ± 0.14). Similarly, six out of eight conditions resulted in lower muscle activation from the semitendinosus with the apparatus. For the semitendinosus muscle, the range was from 43.9% beneficial to 0.1% beneficial (semitendinosus mean: With device 0.327 mV ± 0.09 and without device 0.339 mV ± 0.09). Conclusion: The reduction in electrical activity of the biceps femoris and the semitendinosus during the isometric hold with the Hamstring apparatus suggests that the elastic hamstring assistance device effectively assists in knee flexion and could potentially be used for rehabilitation purposes.
Keywords: Elastic resistance, hamstrings, isometric, rehabilitation
|How to cite this article:|
Bellar D, LeBlanc N, Judge LW. Examination of muscle activity with an elastic hamstring assistance device. J Health Res Rev 2014;1:20-4
|How to cite this URL:|
Bellar D, LeBlanc N, Judge LW. Examination of muscle activity with an elastic hamstring assistance device. J Health Res Rev [serial online] 2014 [cited 2020 Jul 11];1:20-4. Available from: http://www.jhrr.org/text.asp?2014/1/1/20/143321
| Introduction|| |
Hamstring injuries are prevalent in both team sports and sports where repeated sprint efforts are required. , These injuries occur at a high frequency, and have been recently reported to account for 29% of all injuries in athletes.  This finding was supported by data collected from the 2011 International Association of Athletics Federations (IAAF) World Championships held in Daegu, Korea where of 185 injured athletes, the most prevalent diagnosis was a hamstring strain.  These injuries are also associated with recurrence after return to play. Recent data collected from 1999 to 2007 on elite track and field athletes suggests that during a 24-month period after injury, 13.9% of athletes re-presented a hamstring strain in the same limb. 
Hamstring strains are thought to occur during the terminal phase of the gait cycle, where the hamstrings are lengthening in preparation for ground contact. ,, There is limited evidence in literature on the predictive tests for hamstring strains.  Hamstring flexibility and hamstring to quadriceps strength ratio are the two common evaluations used; however, definitive evidences for the predictive value of these measures are yet to surface.  Some research has suggested that a focus on eccentric strength exercises may have protective effects against hamstring strains. , Given the lack of clear evidence for prediction of hamstring strains, it is likely that these injuries will continue to plague athletic populations. Therefore, it is important to examine the treatment of such injuries to enhance rehabilitation.
Strain injuries in the hamstrings are often treated through stretching and strengthening exercise after the initial inflammation and pain from the injury has been managed.  Both protocols have been shown to be effective in treating injuries; however, protocols that address strengthening and muscle dysfunction have demonstrated reduced injury recurrence. 
Exercises that have both eccentric and concentric phases are often incorporated after pain has been reduced and the range of motion (ROM) restored post injury.  It has been stated that one of the primary goals of hamstring rehabilitation is to strengthen the injured limb throughout the ROM.  A study involving an elite group of Swedish football players concluded that lengthening exercises during rehabilitation resulted in faster return to play as compared to concentric-based exercises.  Given that the hamstrings are exposed to lengthening during high-speed running, these results are not at all surprising. ,,
Functional movements, those that mimic natural movement patterns, are gaining popularity in rehabilitation programs.  The hamstring is a biarticulate muscle with action in the knee and hip joints.  Traditional multi-joint closed chain exercise offers the ability to simultaneously articulate the hip and knee joints and has both eccentric and concentric phases for the thigh muscles.  Rehabilitation programs that incorporate both open and closed chain exercises have been shown to be more effective that those involving closed chain exercises alone.  However, the necessary time to include open chain kinetic exercise during rehabilitation has yet to be determined, as both early and late start programs have not been shown to differ. ,
The available evidence indicates that a rehabilitation exercise that is biarticulate and offers an open chain or swing phase component might be ideally suited to hamstring strain rehabilitation, in conjunction with traditional closed kinetic chain and stretching exercises. The goal of the present investigation was to evaluate the ability of an elastic resistance based device to reduce hamstring muscle activity during isometric exercise. The design of the device to be tested allows for biarticulate, open chain exercises. Anecdotal evidence based upon rehabilitative use suggests the device is effective in reducing the work of the hamstrings during these types of movements and allows an early return to functional movements. However, the device has yet to be formally investigated. This device, if effective, could allow for an assisted return to functional movements earlier in the course of hamstring strain rehabilitation.
| Materials and methods|| |
Approach to the problem
The experimental protocol was a cross-over design with random order of treatment (hamstring assistance device vs. control). Participants reported to the Human Performance Lab complex on two occasions. The first visit was an initial data collection and familiarization visit. During the initial visit, maximum voluntary isometric force at 90° and 135° of knee extension was determined, and the participant was fitted with the hamstring assistance device and allowed to perform knee flexions and extensions to become comfortable. This movement allowed for familiarization with the fit and feel of the device and its use in knee articulation. During the second visit, the participants performed isometric holds at multiple joint angles with multiple loads, either with the hamstring assistance device or with no device (control), separated by 30 min of rest using the left leg. The isometric holds were performed both at 90° and 135° of knee extension with a weight attached to the ankle via a strap and a load representing 15%, 30%, 45%, and 60% of their pre-determined maximum isometric force. Isometric exercise was chosen to allow for better quality of capture using electromyography (EMG). EMG was used to monitor the activity in the biceps femoris and semitendinosus muscles during the isometric holds.
Twelve apparently healthy college students of average height and weight were recruited to participate in the study. The subjects had the experimental protocol explained to them, and gave written informed consent before the study began. All 12 subjects completed the protocol.
Determination of maximum isometric strength
To determine the subjects' peak isometric force at each joint angle, a goniometer (Lafayette Instruments, Lafayette, IN, USA) was used to set the joint to either 90° or 135° of extension. Afterward, the ankle was fixed to a load cell (iLoad Pro; LoadStar Sensors, Fremont, CA, USA) sampling at 133 Hz and the subject was instructed to pull against the chain with the heel as hard as possible for a duration of 3 s, or until the force production noticeably declined (drop of greater than 5 kg from the peak value). The peak force was selected and percentages of this force (in kilograms) were used to set the weight for the isometric exercise protocol.
Isometric exercise protocol
Subjects were asked to perform an isometric exercise protocol during the second lab visit. The protocol involved exercise with various weights (percentages of isometric maximum force) at both 90° and 135° of knee extension. The exercise was performed both with the hamstring assistance device and without it. The participants performed the protocol twice using their left leg with a 30-min rest period between each. The participants wore the hamstring assistance device during one protocol and had no device during the other (control). The protocol involved one isometric hold with (in order) 15%, 30%, 45%, and finally 60% of their peak isometric force in kilograms at 90° of knee extension followed by 135° of knee extension. The weights were secured via an ankle strap, with a chain threaded through the weights. Fractional plates were used to allow for adjustments as small as 0.1 kg. All weights were first held at 90°, followed by a short rest (5 min), and then repeated at 135° of knee extension. The subjects were instructed to hold the weight motionless, and the researcher signaled for the subject to relax after a representative EMG signal capture was acquired. The order (hamstring assistance device, control) was randomized.
Hamstring assistance device
The hamstring assistance device consisted of a cuff that was secured below the patella with hook and loop straps, and a belt secured about the hips (weightlifting style). Anchors for Theraband Silver elastic bands (The Hygenic Corporation, Akron, OH, USA) were attached to both the belt and the cuff. This allowed the band to supply assistance with both hip extension and knee flexion, mimicking the biarticulate nature of the hamstring muscle group. The manufacturer quotes that 4.6 kg of force is required for 100% elongation of the material. For the device, two lengths of the elastic band were used in tandem and were pre-stretched to approximately 150% elongation. The estimated force supplied by the device would be 13.8 kg at the onset of the exercise [Figure 1].
Surface electromyography (sEMG) was acquired using a Biopac MP150A (Biopac systems Inc., Goleta, CA, USA) system using AcqKnowledge software. Disposable Ag-AgCl surface electrodes were used during the testing and remained in place throughout data collection. The skin surface was prepared by cleansing with a disposable wipe saturated with isopropyl alcohol, and excess hair was removed with a disposable razor as needed and NuPrep skin gel applied (Weaver and Company, Aurora, CO, USA).
Electrodes were located 20 mm apart in a bipolar configuration in accordance with the recommendation of the Seniam Group.  Readings were low-pass filtered and amplified prior to data analysis. The AcqKnowledge software was used to locate rectified Peak sEMG signals from each muscle after isometric exercise.
Data from the AcqKnowledge software were imported into SPSS (IBM SPSS Statistics for MacIntosh, Version 21.0; IBM Corp., Armonk, NY) for analysis. Data were analyzed for normality with Shapiro-Wilks tests and then analyzed with paired samples t-test. These tests are presented as calculated, as most recent evidence has suggested an unwarranted inflation in type II error using adjusted P values.  Finally, clinical inferences based upon effect size were calculated for each muscle, based upon the work of Hopkins. 
| Results|| |
Initial examination of the data with Shapiro- Wilk test of normality (P > 0.05) did not suggest the need for non-parametric analysis, therefore planned examination with paired samples t-tests was undertaken.
There was a significant difference in the signal from the biceps femoris determined via surface electromyography (sEMG) at 90 degrees of knee extension using 30% of peak isometric force as the load (P = 0.0439). Additionally in the biceps femoris there were differences in the sEMG signal at 135 degrees of knee extension using 15% (P = 0.0492) and 30% (P = 0.0358) of peak isometric force. In the semitendinosus muscle, there was a significant difference in sEMG signal at 15° of knee extension with 60% of peak isometric force (mean diff.: 0.1421 mV; P = 0.0025). One other measure approached significance with P < 0.1 [Table 1].
|Table 1: EMG results from isometric protocol of muscle, knee angle, and percentage of maximum isometric peak force |
Click here to view
Overall, clinical inferences revealed that the device could be considered 71.4% beneficial or substantially positive to 10.9% for reducing the sEMG signal associated with isometric exercise in the biceps femoris (biceps femoris mean: With device 0.319 mV ± 0.13 and without device 0.361 mV ± 0.14). The odds ratio for benefit to harm was 35:1 using the device to lower activity in the biceps femoris.
Similarly, six out of eight conditions resulted in lower muscle activation from the semitendinosus with the apparatus. For the semitendinosus muscle, the range was from 43.9% beneficial to 0.1% beneficial (semitendinosus mean: With device 0.327 mV ± 0.09 and without device 0.339 mV ± 0.09). The odds ratio for benefit to harm was 5:1 using the device to lower activity in the semitendinosus.
| Discussion|| |
The results of the present investigation are promising in regard to the use of the hamstring assistance device to assist in rehabilitation. The device demonstrated some statistically significant decreases in muscle activity with isometric exercise, and overall there was a trend across most joint angles and loads for reduced signal from the hamstring group. Based upon this finding, this device could be used to assist returning an athlete to sport or perform functional movements earlier in a rehabilitation program. Some evidence does exist for the inclusion of these types of movements in a rehabilitation program from acute hamstring strains. Sherry and Best  examined two protocols, one involving stretching and strengthening and the other involving progressive involvement of agility and trunk stabilization exercises. They reported that after 1 year, the injury recurrence rate was higher (70% vs. 7.7%) in the stretching and strengthening group as opposed to the group that participated in agility movements. The hamstring assistance device evaluated in this study could find use in the initial phase of introducing agility exercise to a rehabilitation program. The device if used during recovery could reduce the reduction in neural drive associated with limb disuse. An evidence from a study of plantar flexion after prolonged unweighting of the leg suggests that 48% of the variability in strength change was due to neural factors (H-reflex wave).  This suggests a plausible benefit of using the hamstring assistance device to facilitate a return to functional movements, as nervous system function could begin to adapt to the new stimulus while the contractile tissue was being assisted by the elastic properties of the device. These movements are gaining popularity in rehab programs and the evaluated device is unique in its ability to assist the biauriculate nature of the hamstring group. , Functional movements and traditional multi-joint closed chain are effective in working articulations of the hamstring with both eccentric and concentric phases.  The return to these forms of exercise could be facilitated given the design of the device (assists in knee flexion, hip extension).
The present investigation is not without limitations. A small sample of healthy males was used in this exploratory evaluation; therefore, studies with larger samples are warranted. The device was assessed using a static or isometric exercise. Though this does limit the ability to generalize the findings to all forms of movement, these exercises facilitate the capture of sEMG data.  Given the novelty of the device, the decision was made to capture as clean an sEMG signal as possible to determine if the device was functional. A convenience sample of subjects was used to evaluate the device; so, the results may not be representative of those in an athletic population. Taking these into consideration, the present investigation suggests that these devices may have a future role in rehabilitation of hamstring strains and that future studies on similar devices are warranted.
The reduction in electrical activity of the biceps femoris and the semitendinosus during the isometric hold with the Hamstring apparatus suggests that the elastic hamstring assistance device effectively assists in knee flexion and could potentially be used for rehabilitation purposes. Though further investigation into this device and similar devices is warranted, the device could potentially reduce the work of the hamstrings to enhance the ability of a person with a hamstring strain to return to functional activities and movements. Based upon the current evidence, this may assist in rehabilitation.
| Acknowledgment|| |
The Hamstrong Group funded the present investigation. However, the authors did not have any conflicts of interest in conducting the study.
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