Abstract
Background: Hamstring injuries are common injuries in sports involving sprinting, high-velocity running and kicking. Assessment and rehabilitation of hamstring injuries follow multi-factorial strategies that include examination of hamstring neuromotor control and strength. Recent literature has also emphasised examination of lumbopelvic spine biomechanics and motor control as potential factors contributing to hamstring injury. Recent evidence suggests that external pelvic compression (EPC) with a pelvic compression belt (PCB) can augment the stability of the pelvic joints, and alter neuromotor control of the lumbopelvic and thigh muscles including the hamstrings in individuals with and/or without lumbopelvic and groin pain associated with somatic dysfunction. Previous research has shown that injured hamstrings can demonstrate increased electromyographic (EMG) activity during a weight-bearing task such as transition from bipedal to unipedal stance (BUS), and generate decreased isokinetic eccentric torque in the terminal range of knee motion when compared to control participants. However, evidence to support alterations in neuromotor control of injured hamstrings during walking remains equivocal. If EPC using a PCB can correct aberrations in EMG activity and strength of injured hamstrings then it would have some implications for using a PCB in hamstring injury rehabilitation.
Aims: The aims of this study were to investigate how application of a PCB might influence EMG activity of the hamstrings during BUS, and during a walking task, and affect torque generation of the thigh muscles during isokinetic testing of the knee in sportsmen with and without hamstring injuries. In addition to the hamstrings, the lumbar multifidi and gluteal muscles were also examined by EMG analysis to understand the changes occurring with EPC in lumbopelvic and proximal lower limb kinetic chain during weight-bearing tasks.
Methods: A systematic review of literature was carried out to corroborate the evidence substantiating the effects of EPC on form closure and force closure of the lumbopelvic spine, and neuromotor control of the lumbopelvic and thigh muscles. A simultaneous exploration of literature was undertaken to understand the plausible hypothetical mechanisms underpinning the effects of EPC on the hamstrings. As the amount of PCB tension was thought to influence outcome variables, a study was done on 10 healthy participants to determine the tension that could be achieved during the tasks included in this research. Thirty healthy participants (control group) and 20 participants with previous hamstring injuries (17 unilateral and 3 bilateral injuries; hamstring-injured group) were recruited for the main study. Each participant performed two weight-bearing tasks (BUS followed by walking) in the first session and underwent isokinetic testing of the knee in the second session, which was conducted within the following seven days. Maximum voluntary isometric contraction normalised EMG amplitudes of the biceps femoris, medial hamstrings, gluteus maximus, gluteus medius, and lumbar multifidus during weight-bearing tasks and body weight normalised torque (concentric quadriceps and concentric and eccentric hamstrings) data during isokinetic testing of the knee were collected from one side of healthy participants and both sides of hamstring-injured participants. Prior to investigating the effects of EPC on outcome variables, between and within group differences were explored using no belt trials. Independent t tests were used to compare the no belt trials of the injured side of hamstring-injured group (n = 22) and the tested side of control group (n = 30). Paired t tests were used for comparing no belt trials of the injured and uninjured sides of participants with unilateral hamstring injury (n = 17), and trials with and without the PCB for the outcome variables. Confidence intervals and effects sizes were also used to aid interpretation of the results.
Results: There was no significant difference for EMG activity (BUS and walking) of the hamstrings between groups for any of the outcome variables based on no belt trials. However, compared to uninjured hamstrings, injured hamstrings were found to be weaker during concentric (p = 0.020) and (terminal range) eccentric (p = 0.040) contractions in participants with unilateral hamstring injury. Application of the PCB increased biceps femoris (p = 0.027) and gluteus maximus (p = 0.023) activity on the injured side of the hamstring-injured group but not for the control group during BUS. Though no change was evident for hamstring activity, there was an increase in gluteus medius EMG activity during the loading response phase in both hamstring-injured (p = 0.003) and control (p = 0.028) groups while walking. Gluteus maximus activity was also increased with the PCB in the control group (p = 0.025) while walking. In addition, there was a decrease in multifidus activity during BUS (p = 0.023) and walking (terminal swing and loading response phase; p < 0.001) with the PCB among control participants. With the PCB, there was an increase in normalised average torque of terminal range eccentric hamstring contractions in the hamstring-injured (p = 0.003) and control (p = 0.044) groups, and normalised peak torque of eccentric hamstring contractions in the hamstring-injured group (p = 0.025).
Conclusion: The application of the PCB was found to increase biceps femoris and gluteus maximus activity on the injured side of the hamstring-injured group during BUS, gluteus medius activity during walking, and terminal range eccentric hamstring strength in both control and hamstring-injured groups. Furthermore, with the PCB, gluteus maximus activity was increased during BUS, and multifidus activity was decreased during BUS and walking among control participants. However, the PCB did not alter hamstring activity in both groups during walking.
Inference: This research provides preliminary evidence that application of a PCB can improve outer range eccentric strength of the hamstrings. The benefit of using a PCB to alter neuromotor control of the hamstrings during weight-bearing tasks is unclear as there was no evidence of change in EMG amplitudes of the hamstrings between control and injured participants. However, future studies are warranted to investigate the effects of the PCB on eccentric strength training of the hamstrings, EMG onsets of the hamstrings during BUS and EMG amplitudes of the hamstrings during different walking speeds.