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Tuesday, June 6, 2023

Activation of Forearm Muscles for Wrist Extension in Patients Affected by Lateral Epicondylitis

Brent Brookbush

Brent Brookbush


Research Review: Activation of Forearm Muscles for Wrist Extension in Patients Affected by Lateral Epicondylitis

By Nate Missler MOT, OTR/L

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

Original Citation: Rojas, M., Mananas, M.A., Muller, B., Chaler, J. (2007). Activation of Forearm Muscles for Wrist Extension in Patients Affected by Lateral Epicondylitis. 2007 29th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2007, 4858-4861. ABSTRACT

Why the Study is Relevant: Lateral epicondylitis (LE), also known as “tennis elbow”, is an upper extremity injury commonly related to work and sport activities (1,2). LE is hypothesized to result from overload of the extensor carpi radialis longus and brevis, extensor carpi ulnaris and extensor digitorium communis (1). This 2007 study used surface electromyography (EMG) to investigate muscle co-activation and myoelectric fatigue during a range of isometric contractions. The findings demonstrate altered forearm muscle activity in those with LE when compared to healthy individuals. This information may aid human movement professionals in designing LE rehabilitation and/or prevention programs.

Flexor Carpi Radialis Activation performed by Krystal Salvent with instruction from Dr. Brookbush (c) Brookbush Institute

Study Summary

Study DesignRepeated Measures Design
Level of EvidenceIIA Evidence from at least one controlled study without randomization
Participant CharacteristicsDemographics
  • Number of participants: 20 males, 10 presenting with Lateral Epicondylitis (LE) and 10 healthy.

LE group:

  • Age: mean ± SD: 31.5 ± 5 years
  • Height: 176.4 ± 6.15cm
  • Weight: 76.3 ± 5.48kg
  • Inclusion Criteria:
    • History of conservative treatment for LE
    • Free of LE related symptoms for at least 3 months
    • Lesion has been induced by repetitive use of forearm muscles in physical efforts required by daily or sports activities.

  • Exclusion Criteria: Surgical history for LE

Healthy group:

  • Age: 33.3 ± 4.6 years
  • Height: 174.6 ± 5.8cm
  • Weight: 76.92 ± 12.8kg
  • Inclusion Criteria:
    • No history of musculoskeletal and/or neuromuscular disorder.
    • Lesion is the result of repetitive use of forearm muscles during daily activity or sport.

MethodologyPrior to Testing:
  • To ensure proper electrode placement, muscle contraction during the following motions was recorded:
    • Radial deviation
    • Finger extension
    • Ulnar deviation

  • Electrodes were placed over the based on placements used in a previous study (3):
    • extensor carpi radialis
    • extensor digitorium communis
    • extensor carpi ulnaris


  • Participants sat with straight backs.
  • The dominant arm was placed into an isometric brace, with the forearm pronated and 90° of elbow flexion.
  • Participants extended the wrist in a vertical direction, parallel to the forearm line.
  • Torque was measured on both sides of the hands to reduce wrist rotation
  • A total of 9 contractions were completed:
    • Selective contractions of radial deviation, finger extension and ulnar deviation
    • Participants in both groups performed 3 trials of their maximum voluntary contraction (MVC) for wrist extension
    • Submaximal contractions of 20%, 50% and 80% MVC were then completed in random order.

  • MVC was maintained for 15 seconds, or to exhaustion, followed by a 3-minute rest period.
Data Collection and AnalysisData Collection:
  • Two 16-channel amplifiers (ASE16, LISiN-SEMA Electtronica, Torino, Italy) were used to record EMG.
  • Linear arrays of 8 AgAgCl surface electrodes (LISiN-Spes Medica, Italy) were used for EMG input.
  • EMG signals were bandpass filtered in a single differential mode (SD) and stored on a computer after a 12-bit analog-to-digital conversion transfer (National Instrument NI-DAQ 6024E and NI-DAQ AI-16E4 cards).

EMG Data Analysis:

  • EMG signal amplitude was estimated through average rectified value (ARV).
  • Median (MDF) and mean frequencies (MNF) were calculated from the power spectrum of the EMG signals.
  • Conduction velocity (CV) of the muscle fiber was computed using a matching algorithm by McGill et al (4).

Statistical Analysis:

  • Intragroup statistics were performed through the Wilcoxon Signed Rank test.
  • Mann-Whitney U test was performed between the two groups.
  • Level of significance was set to p <0.05.
Outcome MeasuresMuscle Co-activation
  • The most active extensor muscle was determined using average EMG values during six exercises (radial and ulnar deviation, finger extension and three wrist extension exercises at submaximal level).
  • In each exercise, the average EMG of the muscle being examined was normalized by the sum based on the contraction task.

Myoelectric Fatigue

  • To record the fatigue index, the change in EMG variables over time during the 80% MVC wrist extension test was analyzed between the two groups and their individual muscles respectively.
ResultsMuscle Co-activation
  • LE group mean EMG activity was higher in the extensor carpi ulnaris than in the extensor digitorum communis at 20, 50 and 80% MVC (P<0.02), and higher than extensor carpi radialis at 20% MVC (P<0.05).
  • The healthy group produced higher mean EMG of the extensor carpi radialis than the extensor digitorum communis at all MVC levels, and greater extensor carpi ulnaris co-activation at 80% MVC.
  • The average contribution of the extensor carpi radialis was greater for healthy participants than for those in the LE group, and the extensor carpi ulnaris contribution was greater for the LE group than for healthy participants.

Myoelectric Fatigue

  • In both groups, decreased conduction velocity was noted during the fatiguing exercise protocol in all muscles (P<0.02).
  • Mean and median frequencies decreased and average EMG variables increased in the LE group but not among healthy participants.
  • Increased average EMG in extensor carpi radialis, extensor carpi ulnaris and extensor digitorium communis demonstrated as higher fatigue indexes for LE group than for healthy subjects.
Our ConclusionsThe average contribution of the extensor carpi radialis was greater for healthy participants than for those in the LE group, and the extensor carpi ulnaris contribution was greater for the LE group than for healthy participants.
Researchers' Conclusions

The findings suggest that in individuals with LE, muscular imbalance with lower extensor carpi radialis activity is compensated by higher extensor carpi ulnaris activation, and higher fatigue indexes.

Review & Commentary:

The following movements were used to compare the performance between asymptomatic participants and those exhibiting signs of (LE): radial deviation, ulnar deviation, finger extensions, and three wrist extension exercises at submaximal levels. The findings suggest that LE correlates with lower extensor carpi radialis activity, higher extensor carpi ulnaris activity, and greater neuromuscular indicators of extensor fatigue.

  • This study had many strengths:
    • To our knowledge, this study is the first to investigate the relationship between neuromuscular fatigue index and LE development.
    • EMG analysis comparing the activity of several extensor muscles allowed for the analysis of compensation patterns adopted by individuals exhibiting signs of LE.
    • The use of several movements/exercises demonstrates that the findings are not specific to a particular exercise or piece of equipment.
  • Weaknesses that should be noted prior to clinical integration of the findings include:
    • The research study did not test exercises commonly used in a rehab or performance setting, decreasing applicability of study findings.
    • Only isometric contractions were evaluated. Future research should also assess dynamic (both concentric and eccentric) contractions.
    • Neuromuscular fatigue parameters were not correlated with clinically observable visual cues/changes in motion.

How This Study is Important:

This study adds to a growing body of research on lateral epicondylitis (LE) (1-3 5). This study compared muscle activity of the extensor carpi radialis, extensor digitorum communis, and extensor carpi ulnaris during six isometric motions to fatigue. The comparison of multiple extensor muscles resulted in the identification of a compensatory pattern noted in those with LE. In LE participants, the extensor carpi radialis demonstrated lower relative activity to the extensor carpi ulnaris with greater indicators of neuromuscular fatigue in all extensors.

How the Findings Apply to Practice:

The findings imply that it may be advisable to select techniques that increase extensor carpi radialis activity, decrease extensor carpi ulnaris activity and increase endurance of extensors. This may include extensor carpi ulnaris release, wrist/elbow joint mobilizations, extensor carpi radialis activation and integration/conditioning techniques to improve over-all endurance.

How does it relate to Brookbush Institute Content?

The Brookbush Institute (BI) uses an integrated approach when addressing movement impairment . Although a predictive model of forearm dysfunction is yet to be published, early indicators of osteokinematic dysfunction include excessive pronation, ulnar deviation and wrist extension (5). This study supports the BI’s initial findings, demonstrating a decrease in extensor carpi radialis activity and increase in extensor carpi ulnaris activity during several movement patterns.

The BI addresses over-active muscle groups with release techniques and under-active muscles with activation techniques, further, joint mobilizations and integration/conditioning techniques may aid in optimizing motion and performance. The following videos illustrate recommended self-administered release and activation exercises for elbow/forearm/wrist dysfunction.

Wrist Extensor Self-administered Static Release

Flexor (Wrist) Activation

Flexor Carpi Radialis Activation

Supinator Activation

Reverse Tyler Twist - Wrist Flexor Isolated Activation


  1. Tosti, R., Jennings, J., Sewards, J.M. (2013). Lateral Epicondylitis of the Elbow. The American Journal of Medicine, 126(4), 157.e1-157.e6.
  2. Institute of Medicine and National Research Council. (2001). Muscloskeletal Disorders and the Workplace: Low Back and Upper Extremities. National Academy Press, 19,165.
  3. Signorino, M., Mandrile., & Rainoldi, A. Localization of Innervation Zones in Forearm Extensor Muscles. A Methodological Study. XVI Congress of the International Society of Electrophysiology and Kinesiology, ISEK.
  4. McGill, K.C., Dorfman, J.L. (1984). High-resolution alignment of sampled waveforms. IEEE Trans BioMed Eng, 31(6), 462-468.
  5. Giffin, J.R., Stanish, W.D. (1993). Overuse Tendonitis and Rehabilitation. Canadian Family Physician, 39, 1762-1769.
  6. Leversedge, F.J., Goldfarb, C.A., & Boyer, M.I. (2010). A Pocketbook Manual of Hand and Upper Extremity Anatomy. Lippincott Williams & Wilkins, 75.

© 2018 Brent Brookbush

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