Electromyographic Analysis of Hip and Knee Exercises: a Continuum from Early Rehabilitation to Enhancing Performance
Williams, Megan Rose
Introduction: Muscles around the hip and knee regions work in unison within the kinetic chain to produce functional movements. After a musculoskeletal injury, a progressive programme of rehabilitation exercises should be completed in order to return the athlete to full function. Aims: The primary aim was to identify a progressive continuum of lower limb exercises. A secondary aim was to analyse the muscle ratios between the vastus medialis oblique and vastus lateralis, along with the hamstrings to quadriceps ratio and the gluteus maximus to biceps femoris ratio. Objectives: Electromyography (EMG) was used to monitor the activity of the hip and knee muscles during twenty rehabilitation exercises. The normalised data was used to identify a continuum of exercises, based on the extent to which each muscle was activated. The muscle ratios were also calculated, allowing the identification of a scale of exercises to preferentially activate certain muscles. Subjects: Eighteen physically active volunteers participated in the study (males: n = 9, females: n = 9, mean ± standard deviation, age: 20 ± 1.3 years; height: 168.1 ± 9.7 cm; mass: 64.1 ± 9.8 kg). Method: Surface EMG was used to measure the muscle activity of the gluteus maximus, gluteus medius, biceps femoris, rectus femoris, vastus medialis oblique and vastus lateralis during exercises which ranged between a straight leg raise and a weighted squat. The exercises were performed in a randomised order and three trials were performed of each. The muscle activity was normalised to a maximal voluntary isometric contraction specific for each muscle. The muscle ratios were calculated using specific equations. Results: The counter movement jump and single-leg vertical jump frequently resulted in the production of the greatest EMG activity for each of the muscles, whilst the mini squat produced minimal muscle activity across all of the muscles. The bridging exercises activated the quadriceps to the least extent, resulting in these exercises producing the greatest hamstrings to quadriceps ratio. For the vasti ratio, the single-leg squat to 60° of knee flexion produced the greatest results. The step up exercise produced the highest gluteus maximus to biceps femoris ratio. Conclusions: The continuum of exercises was identified for the activity of each muscle in order to aid clinicians by providing a guide from non weight bearing exercises through to functional jumps. This will ensure exercises are performed at the correct stage of rehabilitation to continually bring about muscular adaptations.