Effect of increasing workload on knee extensor and flexor muscular activity during cycling as measured with intramuscular electromyography.

Julio Cézar Lima Da Silva,Olga Tarassova,Eva Andersson,Helene Grundström,Maria M Ekblom,Anton Arndt,Gustaf Rönquist

doi:10.1371/journal.pone.0201014

Julio Cézar Lima Da Silva, Olga Tarassova + Show 5 more

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https://doi.org/10.1371/journal.pone.0201014

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Abstract

The purpose of this study was to describe the effect of increasing workload on individual thigh muscle activation during a 20 minute incremental cycling test. Intramuscular electromyographic signals were recorded from the knee extensors rectus femoris, vastus lateralis, vastus medialis and vastus intermedius and the knee flexors semimembranosus, semitendinosus, and the short and long heads of the biceps femoris during increasing workloads. Mean activation levels were compared over the whole pedaling cycle and the crank angles at which onset and offset of activation and peak activity occurred were identified for each muscle. These data were compared between three workloads. EMG activation level significantly increased (p<0.05) with increasing workload in the rectus femoris, vastus medialis, vastus lateralis, vastus intermedius, biceps femoris long head, semitendinosus and semimembranosus but not in the biceps femoris short head. A significant change in activation timing was found for the rectus femoris, vastus lateralis, vastus medialis and semitendinosus. Of the knee flexors only the short head of the biceps femoris had its peak activity during the upstroke phase at the two highest workloads indicating a unique contribution to knee flexion.

Highlights

In cycling, muscle recruitment behavior and muscle coordination have been shown to depend upon training level, cycling modality and intensity [1]
All superficial muscles showed significant adaptations with increased workload, while for the deep muscles significant changes in mean EMG activation were only found for the vastus intermedius (Vint)
The bi-articular rectus femoris (RF) increased its mean EMG activation level across workloads and its activation pattern was similar to the results reported by Blake, Champoux [9] who suggested that the RF contribution to the power output during cycling increases already before the top dead center (TDC) and continues into the downstroke phase

Summary

Introduction

Muscle recruitment behavior and muscle coordination have been shown to depend upon training level, cycling modality and intensity [1]. Muscle activation will need to adapt to changes in workload and muscular fatigue [4]. A number of studies have shown an increase in muscle activation amplitude as measured via surface electromyography (EMG) when increasing the workload [3, 5–. With increasing fatigue the cyclist requires a neuromuscular strategy for modifying motor unit recruitment and EMG activity to maintain the greatest possible power production [13]. Such adaptations might have consequences upon the synergy between deep and superficial muscles and there is at present little research on the timing of superficial and deep thigh muscle activation during cycling [13]

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