Original article
Nonuniform Activity of Human Calf Muscles During an Exercise Task

Presented to the Society for Neuroscience, November 9, 2000, New Orleans, LA.
https://doi.org/10.1016/j.apmr.2005.04.012Get rights and content

Abstract

Segal RL, Song AW. Nonuniform activity of human calf muscles during an exercise task.

Objectives

To determine the distribution of leg muscle activity during heel raises using magnetic resonance imaging (MRI) with special emphasis on quantifying activity across multiple axial sections and to determine if there are differences among portions of active muscles.

Design

Pre- and postexercise (heel raise) T2-weighted time measurements were assessed by using repeated-measures analysis of variance (ANOVA) and t tests.

Setting

Laboratory and MRI suites.

Participants

Eight healthy volunteers.

Intervention

Unilateral heel raises every 2 seconds for at least 60 seconds.

Main Outcome Measures

Percentage changes from T2-weighted magnetic resonance images of the lateral gastrocnemius, medial gastrocnemius, peroneus longus, soleus, and tibialis anterior muscles, across 10 axial sections, exercise bouts, and a pre-exercise condition.

Results

The lateral gastrocnemius, medial gastrocnemius, peroneus longus, and soleus had significantly larger changes in T2 time from pre-exercise times than did the tibialis anterior for whole muscles as determined by using repeated-measures ANOVA and post hoc analyses. The medial gastrocnemius had a significantly greater change in T2 time than the lateral gastrocnemius. Proximal axial sections of the lateral gastrocnemius, medial gastrocnemius, and soleus had significantly larger changes in T2 time from pre-exercise than did distal sections.

Conclusions

This work reconfirms that multiple muscles contribute to plantarflexor forces and additionally shows an apparent proximal versus subvolume organization of activity within the gastrocnemius, medial gastrocnemius, and soleus but not the peroneus longus. This proximal versus distal organization of muscle activity needs further investigation. There may be clinical implications for therapeutic interventions that require accurate placement of electrodes such as biofeedback.

Section snippets

Overview

All subjects had pre- and postexercise T2 sequences and pre-exercise T1 sequences of the right or both legs while secured in a volumetric coil. The T1-weighted images were used to help define the anatomy within axial sections. Subjects performed heel raises after the pre-exercise scans. T2-weighted sequences were performed immediately after each exercise bout, and there was a rest period of at least 40 minutes between exercise bouts. Forty minutes of rest was chosen because T2 time recovers

Results

Two subjects were not used for analysis because their pre-exercise images had extensive noise that made these sections unreliable to use as the baseline measurement to determine percentage change with exercise.

Discussion

There are many muscles that can contribute to the plantarflexion force necessary for heel raises, including those muscles analyzed in our study. All of these muscles had changes in T2 time, but the changes were not equal among muscles and there was some intersubject variability. In particular, the medial gastrocnemius was more active than the lateral gastrocnemius. In addition, the peroneus longus, which is typically thought of as primarily an evertor or abductor of the foot, is active. Most

Conclusions

Because multiple muscles usually contribute to a movement, knowledge of the global functioning (organization of whole limb or segment) of the neuromuscular system is critical for understanding normal movement and developing new treatments and evaluative tools for patients. Thus, we must be able to simultaneously determine the activity of many spatially dispersed groupings of active muscle units. Traditional electromyographic recording techniques have been used to try to determine global

Acknowledgments

We thank Marsha Ward and Janet Kindschuh for technical assistance, Sara Giordano for comments on the manuscript, and George Cotsonis for help with statistical analyses and interpretation.

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    Supported by the National Institute of Child Health and Human Development (grant no. HD 32571).

    No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the authors(s) or upon any organization with which the author(s) is/are associated.

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