Impact of exercise selection on hamstring muscle activation

Pain-Free Versus Pain-Threshold Rehabilitation Following Acute Hamstring Strain Injury: A Randomized Controlled Trial

STUDY DESIGN

Randomized controlled trial.

BACKGROUND

Conventional guidelines recommend hamstring strain injury (HSI) rehabilitation should only be performed and progressed in complete absence of pain, despite lack of comparison to alternative approaches.

OBJECTIVES

The primary aim of this study was to compare the number of days from acute HSI to return to play (RTP) clearance following a standardised rehabilitation protocol performed within either pain-free or pain-threshold limits. The secondary aims were to compare isometric knee flexor strength, biceps femoris long head (BFlh) fascicle length, fear of movement and re-injury during a six-month follow-up between pain-free and pain-threshold groups.

METHODS

Forty-three men with acute HSIs were randomly allocated to either a pain-free (n=22) or pain-threshold (n=21) rehabilitation group. Days from HSI to RTP clearance, isometric knee flexor strength, BFlh fascicle length, fear of movement and re-injuries within six-month follow-up were reported.

RESULTS

The median time from HSI to RTP clearance was 15 days (95% CI = 13 to 17) in the pain-free group and 17 days (95% CI = 11 to 24) in the pain-threshold group, which was not significantly different (p = 0.37). Recovery of isometric knee flexor strength at 90/90 degrees of hip/knee flexion was greater in the pain-threshold group at RTP clearance by 15% (95% CI = 1 to 28) and by 15% (95% CI = 1 to 29) at two-month follow-up. BFlh fascicles were 0.91cm (95% CI = 0.34 to 1.48) longer at two-month follow-up in the pain-threshold group. Two re-injuries occurred in both the pain-free and pain-threshold group during six-month follow-up.

CONCLUSION

Pain-threshold rehabilitation did not accelerate RTP clearance but did result in greater recovery of isometric knee flexor strength and better maintenance of BFlh fascicle length improvements compared to pain-free rehabilitation. J Orthop Sports Phys Ther, Epub 28 Jun 2019. doi:10.2519/jospt.2019.8895.

Eccentric knee flexor weakness in elite female footballers 1-10 years following anterior cruciate ligament reconstruction

OBJECTIVES

To determine eccentric knee flexor strength in elite female Australian Rules Football (ARF) players with and without a history of unilateral anterior cruciate ligament reconstruction (ACLR) using an ipsilateral semitendinosus graft.

DESIGN

Case-control.

SETTING

Elite ARF Women's competition.

PARTICIPANTS

Eighty-four elite female ARF players (mean age, 25 ± 4.9 years; height, 1.71 ± 0.73 m; weight, 67 kg ± 7.4 kg) with (n = 12) and without (n = 72) a history of unilateral ACLR in the previous 10 years.

MAIN OUTCOME MEASURES

Peak eccentric knee flexor force during the Nordic hamstring exercise (NHE).

RESULTS

Players with a history of unilateral ACLR displayed lower levels of eccentric knee flexor strength in their surgically reconstructed limb than their uninjured contralateral limb (mean difference -53.77 N, 95% CI = -85.06 to -24.27, d = -0.51) and compared to the limbs of players with no history of injury (mean difference = -46.32 N, 95% CI = -86.65 to -11.13, d = -0.73).

CONCLUSION

Elite female ARF players with a history of unilateral ACLR display deficits in eccentric knee flexor strength in their surgically reconstructed limb for up to 10 years following surgery.

Does a bounding exercise program prevent hamstring injuries in adult male soccer players? - A cluster-RCT

Background

Although the Nordic Hamstring Exercise (NHE) prevents hamstring injury in soccer players effectively, the annual incidence of these injuries still increases. This may be because of poor long‐term compliance with the program. Furthermore, the timing and amplitude of gluteal and core muscle activation seem to play an important role in hamstring injury prevention, the NHE program was not designed to improve activation of these muscles. Therefore, we propose plyometric training as an alternative to reduce hamstring injuries in soccer players.

Purpose

To determine the preventive effect of the Bounding Exercise Program (BEP) on hamstring injury incidence and severity in adult male amateur soccer players.

Study design

A cluster‐Randomized Controlled Trial.

Methods

Thirty‐two soccer teams competing in the first‐class amateur league were cluster‐randomized into the intervention or control group. Both groups were instructed to perform their regular training program, and the intervention group additionally performed BEP. Information about player characteristics was gathered at baseline and exposure, hamstring injuries and BEP compliance were weekly registered during one season (2016‐2017).

Results

The data of 400 players were analyzed. In total, 57 players sustained 65 hamstring injuries. The injury incidence was 1.12/1000 hours in the intervention group and 1.39/1000 hours in the control group. There were no statistically significant differences in hamstring injury incidence (OR = 0.89, 95% CI 0.46‐1.75) or severity between the groups (P > 0.48).

Conclusion

In this large cluster‐randomized controlled trial, no evidence was found for plyometric training in its current form to reduce hamstring injuries in amateur soccer players.

Knee Angle Affects Posterior Chain Muscle Activation During an Isometric Test Used in Soccer Players

Background: It has been suggested that altering the knee flexion angle during a commonly used supine isometric strength test developed with professional soccer players changes preferential hamstring muscle recruitment. The aim of this study was to examine the electromyography (EMG) knee joint-angle relationship during this test, as these data are currently unknown. Methods: Ten recreational male soccer athletes (age: 28 ± 2.4 years) were recruited and performed a supine isometric strength test on their dominant leg with the knee placed at two pre-selected flexion angles (30° and 90°). The surface EMG of the gluteus maximus, biceps femoris, semitendinosus, and medial gastrocnemius was measured, in addition to the within-session reliability (intraclass correlation coefficient (ICC) and coefficient of variation (CV)). Results: Within-session reliability showed large variation dependent upon the test position and muscle measured (CV% = 8.8–36.1) Absolute mean EMG activity and percentage of maximum voluntary isometric contraction (MVIC) indicated different magnitudes of activation between the two test positions; however, significant mean differences were present for the biceps femoris only with greater activation recorded at the 30° knee angle (% MVIC: 31 ± 9 vs. 22 ± 7; p = 0.002). These differences (30% mean difference) were greater than the observed typical measurement error (CV% = 13.1–14.3 for the 90° and 30° test positions, respectively). Furthermore, the percentage MVIC showed a trend of heightened activation of all muscles with the knee positioned at 30°, but there was also more within-subject variation, and this was more pronounced for the gluteus maximus (CV% = 36.1 vs. 19.8) and medial gastrocnemius (CV% 31 vs. 22.6). Conclusions: These results indicate that biceps femoris and overall posterior chain muscle activation is increased with the knee positioned at 30° of flexion; however, the 90° angle displayed less variation in performance within individual participants, especially in the gluteus maximus and medial gastrocnemius. Thus, practitioners using this test to assess hamstring muscle strength should ensure appropriate familiarisation is afforded, and then may wish to prioritise the 30° knee position.

Hamstring Muscle Use in Women During Hip Extension and the Nordic Hamstring Exercise: A Functional Magnetic Resonance Imaging Study

Background Understanding hamstring muscle activation patterns in resistance training exercises may have implications for the design of strength training and injury prevention programs. Unfortunately, surface electromyography studies have reported conflicting results regarding hamstring muscle activation patterns in women. Objectives To determine the spatial patterns of hamstring muscle activity during the 45° hip extension and Nordic hamstring exercises in women using functional magnetic resonance imaging (fMRI). Methods This was a cross-sectional study in which 6 recreationally active women with no history of lower-limb injury underwent fMRI on both thighs before and immediately after 5 sets of 6 bilateral eccentric contractions of the 45° hip extension exercise or the Nordic exercise. Using fMRI, the transverse (T2) relaxation times were measured from pre-exercise and postexercise scans, and the percentage increase in T2 was used as an index of muscle activation. Results The fMRI revealed a significantly higher biceps femoris long head-to-semitendinosus ratio during the 45° hip extension exercise than in the Nordic exercise (P = .028). The T2 increase after the 45° hip extension exercise was greater for the biceps femoris long head (P<.001), semitendinosus, and semimembranosus (P≤.001) than that for the biceps femoris short head. During the Nordic exercise, the T2 increase of the semitendinosus was greater than that of the biceps femoris short head (P<.001) and biceps femoris long head (P = .001). Conclusion While both exercises involve high levels of semitendinosus activation in women, the Nordic exercise preferentially recruits that muscle, while the hip extension exercise more evenly activates all the biarticular hamstrings. J Orthop Sports Phys Ther 2018;48(8):607-612. Epub 23 Apr 2018. doi:10.2519/jospt.2018.7748.

Interseason variability in isokinetic strength and poor correlation with Nordic hamstring eccentric strength in football players

In elite sport, the use of strength testing to establish muscle function and performance is common. Traditionally, isokinetic strength tests have been used, measuring torque during concentric and eccentric muscle action. A device that measures eccentric hamstring muscle strength while performing the Nordic hamstring exercise is now also frequently used. The study aimed to investigate the variability of isokinetic muscle strength over time, for example, between seasons, and the relationship between isokinetic testing and the new Nordic hamstring exercise device. All teams (n = 18) eligible to compete in the premier football league in Qatar underwent a comprehensive strength assessment during their periodic health evaluation at Aspetar Orthopaedic and Sports Medicine Hospital in Qatar. Isokinetic strength was investigated for measurement error, and correlated to Nordic hamstring exercise strength. Of the 529 players included, 288 players had repeated tests with 1/2 seasons between test occasions. Variability (measurement error) between test occasions was substantial, as demonstrated by the measurement error (approximately 25 Nm, 15%), whether separated by 1 or 2 seasons. Considering hamstring injuries, the same pattern was observed among injured (n = 60) and uninjured (n = 228) players. A poor correlation (r = .35) was observed between peak isokinetic hamstring eccentric torque and Nordic hamstring exercise peak force. The strength imbalance between limbs calculated for both test modes was not correlated (r = .037). There is substantial intraindividual variability in all isokinetic test measures, whether separated by 1 or 2 seasons, irrespective of injury. Also, eccentric hamstring strength and limb-to-limb imbalance were poorly correlated between the isokinetic and Nordic hamstring exercise tests.

Region-dependent hamstrings activity in Nordic hamstring exercise and stiff-leg deadlift defined with high-density electromyography

Recent studies suggest region-specific metabolic activity in hamstring muscles during injury prevention exercises, but the neural representation of this phenomenon is unknown. The aim of this study was to examine whether regional differences are evident in the activity of biceps femoris long head (BFlh) and semitendinosus (ST) muscles during two common injury prevention exercises. Twelve male participants without a history of hamstring injury performed the Nordic hamstring exercise (NHE) and stiff-leg deadlift (SDL) while BFlh and ST activities were recorded with high-density electromyography (HD-EMG). Normalized activity was calculated from the distal, middle, and proximal regions in the eccentric phase of each exercise. In NHE, ST overall activity was substantially higher than in BFlh (d = 1.06 ± 0.45), compared to trivial differences between muscles in SDL (d = 0.19 ± 0.34). Regional differences were found in NHE for both muscles, with different proximal-distal patterns: The distal region showed the lowest activity level in ST (regional differences, d range = 0.55-1.41) but the highest activity level in BFlh (regional differences, d range = 0.38-1.25). In SDL, regional differences were smaller in both muscles (d range = 0.29-0.67 and 0.16-0.63 in ST and BFlh, respectively) than in NHE. The use of HD-EMG in hamstrings revealed heterogeneous hamstrings activity during typical injury prevention exercises. High-density EMG might be useful in future studies to provide a comprehensive overview of hamstring muscle activity in other exercises and high-injury risk tasks.

Differences in hamstring activation characteristics between the acceleration and maximum-speed phases of sprinting

This study aimed to investigate activation characteristics of the biceps femoris long head (BFlh) and semitendinosus (ST) muscles during the acceleration and maximum-speed phases of sprinting. Lower-extremity kinematics and electromyographic (EMG) activities of the BFlh and ST muscles were examined during the acceleration sprint and maximum-speed sprint in 13 male sprinters during an overground sprinting. Differences in hamstring activation during each divided phases and in the hip and knee joint angles and torques at each time point of the sprinting gait cycle were determined between two sprints. During the early stance of the acceleration sprint, the hip extension torque was significantly greater than during the maximum-speed sprint, and the relative EMG activation of the BFlh muscle was significantly higher than that of the ST muscle. During the late stance and terminal mid-swing of maximum-speed sprint, the knee was more extended and a higher knee flexion moment was observed compared to the acceleration sprint, and the ST muscle showed higher activation than that of the BFlh. These results indicate that the functional demands of the medial and lateral hamstring muscles differ between two different sprint performances.

Hamstring injuries: update article

Hamstring (HS) muscle injuries are the most common injury in sports. They are correlated to long rehabilitations and have a great tendency to recur. The HS consist of the long head of the biceps femoris, semitendinosus, and semimembranosus. The patient's clinical presentation depends on the characteristics of the lesion, which may vary from strain to avulsions of the proximal insertion. The most recognized risk factor is a previous injury. Magnetic resonance imaging is the method of choice for the injury diagnosis and classification. Many classification systems have been proposed; the current classifications aim to describe the injury and correlate it to the prognosis. The treatment is conservative, with the use of anti-inflammatory drugs in the acute phase followed by a muscle rehabilitation program. Proximal avulsions have shown better results with surgical repair. When the patient is pain free, shows recovery of strength and muscle flexibility, and can perform the sport's movements, he/she is able to return to play. Prevention programs based on eccentric strengthening of the muscles have been indicated both to prevent the initial injury as well as preventing recurrence.