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Tuesday, June 6, 2023

Neuromuscular Activation of Muscles of the Knee during Conventional Therapeutic Exercises and Heavy Resistance Exercises

Brent Brookbush

Brent Brookbush


Neuromuscular Activation of muscle of the Knee during Conventional Therapeutic Exercises and Heavy Resistance Exercises: Implications for Rehabilitation

By Alex Howard PT, DPT, CSCS

Edited by Brent Brookbush DPT, PT, COMT, MS, PES, CES, CSCS, ACSM H/FS

Original Citation: Andersen, L., Magnusson, S., Nielsen, M., Haleem, J., Poulsen, K., & Aagaard, P. Neuromuscular Activation in Conventional Therapeutic Exercises and Heavy Resistance Exercises: Implications for Rehabilitation. Physical Therapy, 86(5), 683-697. ARTICLE

Why is this relevant?:

Quadriceps under-activity, atrophy and a loss of strength are commonly seen following a knee joint injury. Optimal exercise selection is crucial for re-establishing neuromuscular control, and regaining muscle strength and mass. However, most exercises used in a rehabilitation setting do not meet the 40 - 60% maximal intensity required for strength adaptations. This study investigates the level of muscular activation at the knee joint when conventional physical therapeutic exercises and compares them to heavy resistance exercises.

Articularis Genu and the LE -http://www.unmc.edu/dissection/idg33hipknee.cfm
Caption: Articularis Genu and the LE -http://www.unmc.edu/dissection/idg33hipknee.cfm

Articularis Genu and the LE -http://www.unmc.edu/dissection/idg33hipknee.cfm

Study Summary

Study Design Cohort Study
Level of Evidence Level IV - Evidence from well-designed case control or cohort study
Subject Demographics


    • Gender: Male
    • Age: 25.3 (+ 3 years)
    • Weight  75.8 kg (+ 6.2 kg)
    • height  181 cm (+ 4 cm)

Inclusion Criteria:

  • no previous history of knee injury
  • no previous participation  in regular resistance training of lower extremities
Outcome MeasuresPeak EMG signal amplitude for maximal voluntary isometric contraction (MVICs) of knee extensors (quadriceps, vastus lateralis, vastus medialis), hip extensor (gluteus maximus) , and knee flexor (biceps femoris, semitendinosus) muscles were recorded before and after testing
  • Two maximal trials of each exercise
  • Knee extensor muscles (10 and 90 degrees)
  • Knee flexors muscles (10 and 90 degrees)
  • Hip extensor muscles (0 and 90 degrees)

EMG signal data obtained throughout exercises (discussed below using) surface electrode

Three rounds of exercises in cyclic manner with 4 min rest between rounds:

  • Heavy resistance: free weight squat with barbell, isolated knee extension, horizontal seated leg press, hamstring muscle curl
    • Volume: 5 repetitions performed from predetermined 10 repetition maximum (RM)

  • Conventional exercises: pelvic bridging, quadriceps femoris muscle setting, manual lateralization of the patella, rhythmic stabilization
    • Volume: 5 repetitions performed except rhythmic stabilization pressure applied for 15 sec above/below knee at different angles

  • Heavy resistance exercises had greater EMG activity (12-86%) vs conventional exercises (9-34%) through the total range of motion
  • Quadriceps femoris muscle EMG activity was greatest during isolated knee extension (68-74%)
  • EMG amplitude for quadriceps femoris muscle in rank from highest to lowest: isolated knee extension > leg press >squat> quadrcieps femoris muscle setting > manual lateralization of the patella > rhythmic stabilization
  • Vastus medialis (VM) not selectively activated during exercises: VM and vastus lateralis (VL) did not exceed EMG ration of 1.00 at any knee joint angle or in any exercise
  • Hamstring muscle EMG greatest during isolated hamstring curl (67-70%)
  • Hamstring muscle activation during squat (antagonist) vs pelvic bridging exercise (agonist) had similar EMG results: 19-40% vs 24-34%
  • Gluteus maximus muscle EMG activity greatest in squat and leg press (55-60%) vs pelvic bridging (36%)
ConclusionsThis study provides evidence that heavy resistance exercises produce higher levels of neuromuscular activation when compared to conventional therapeutic exercises.  Progression to heavy resistance exercises should be a goal for those recovering from knee injury.
Conclusions of the ResearchersLow levels of neuromuscular activation were observed in conventional therapeutic exercises widely used in physical therapy. High levels of neuromuscular activation were observed in heavy resistance exercises necessary to induce strength gains and muscle hypertrophy following knee joint injuries.

Dr. Brookbush instructs cient on how to perform a Single Leg Squat to Bilateral Cable Pull Down (Posterior Oblique Subsystem Activation Progression)
Caption: Dr. Brookbush instructs cient on how to perform a Single Leg Squat to Bilateral Cable Pull Down (Posterior Oblique Subsystem Activation Progression)

Single Leg Squat to Bilateral Cable Pull Down

Review & Commentary:

The authors of this study examined the neuromuscular activation patterns of various muscles (vastus lateralis , vastus mediali s, rectus femoris , biceps femoris , semitendinosus , and gluteus maximus ) during conventional and heavy resistance exercises commonly used during knee rehabilitation.

There were many strengths to the methodology of this study. The authors used subjects with no prior participation in regular resistance training of the lower extremities, representing a commonly seen population in fitness and rehabilitation setting (the novice lifter), and reducing the affects "practice" may have on activation patterns. Studies have shown subjects with experience in heavy resistance training, display different activation patterns during the exercises used in this study. The authors measured peak EMG levels before and after the exercise trials. The peak EMG amplitudes were not significantly different, suggesting these muscle groups were not fatigued from the beginning to the end of the experiment, and that fatigue did not influence findings.

There were limitations to this study. The authors recruited individuals without a history of knee pain limiting transferability of the study to those individuals with knee pain and injury. It can be assumed that patients with a current knee injury will demonstrate altered levels neuromuscular activation in those muscles crossing the knee and hip, relative to both pre-injury activation levels and relative to one another. Future research should investigate the effectiveness of these exercise in those with knee pain and injury, and include parameters such as pain during activity, tolerance, and compliance. Further, it may be interesting to examine pre- and post-exercise activation during a functional task, and compare those changes to the relative activity of these muscles in "normal" and "injured" controls. Although, heavy resistance exercise may have a greater effect on total muscle activation levels, it may not have a beneficial impact on returning relative activation levels (between muscles) post injury.

Why is this study important?

This research investigates commonly used exercises in the rehabilitation setting. The authors provide evidence that conventional rehabilitation exercises (noted above) do not reach the EMG threshold of 40-60% of maximal voluntary isometric contraction (MVICs), required to stimulate muscle growth and strength gains. This implies that individuals post knee injury should be progressed to strength training exercises (squats, leg press, lunges, etc.) to regain muscle strength and hypertrophy.

How does it affect practice?

The authors findings highlight the the importance of exercise selection in regards to neuromuscular activation of specific muscle groups. Common protocols in rehabilitation focus on selection of the conventional exercises noted above to improve vastus medialis strength, with a goal to improve tracking at the patella. The authors found that with the conventional and heavy resistance exercises the vastus medialis and vastus lateralis EMG ratio did not significantly exceed 1.00. This suggests that no specific exercises researched specifically enhanced vastus medialis neuromuscular activation. The selection of open kinetic chain exercises versus closed kinetic chain produced the highest levels of neuromuscular activation in the quadriceps with isolated knee extension, and in the hamstring with isolated hamstring curl respectively. Novices can safely reproduce these exercises versus the motor control training required to perform a proper squat.

How does it relate to Brookbush Institute Content?

The Brookbush Institute recommends progression of exercise in all rehabilitation and performance programming. Further, all interventions selected should provide a sufficient stimulus to initiate adaptation, that is exercise selection must match the ability of the client/patient and represent an appropriate challenge to their current level of function. Although this study suggests that exercises traditionally used in strength training programs would be better suited for rehabilitation from knee injury, this study does not consider the altered recruitment patterns noted post knee injury or the effect that conventional therapeutic exercise has on altering the relative activity between muscles.

Further, the Brookbush Institute does not advocate treating any joint without consideration of how that joint may be affected by altered movement patterns. Knee dysfunction commonly presents in those exhibiting Lumbo Pelvic Hip Complex Dysfunction (LPHCD), Sacroiliac Joint Dysfunction and/or Lower Leg Dysfunction (LLD), suggesting that the sacroiliac joint, hip, and ankle should be assessed and impairments addressed at a minimum.

This study provides evidence that traditional strength training exercise is an important part of recovery, and that a program designed for full recovery from knee injury should progress to leg press and/or squats.

Below you will find a progression of knee rehabilitation exercises that may be a good prerequisite to larger compound movement patterns like squats and leg press:

Quad Sets and Progressions:

Terminal Knee Extension:

Terminal Knee Extension Progressions:

© 2016 Brent Brookbush

Questions, comments, and criticisms are welcomed and encourage