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Updated: May 9, 2026
14:02
Ex Vivo Assessment of Contractility, Fatigability and Alternans in Isolated Skeletal Muscles
Published on: November 1, 2012
Hot ambient conditions shift the Force / EMG relationship.
1Aspetar, Qatar Orthopaedic and Sports Medicine Hospital, Research and Education Centre, PO Box 29222, Doha, Qatar.
Springerplus
|July 27, 2013
Summary
Elevated core temperature significantly reduced maximal voluntary contraction torque and voluntary activation. Both core and skin warming decreased EMG activity, indicating complex thermal effects on neuromuscular function.
Area of Science:
- Physiology
- Exercise Science
- Neuromuscular Physiology
Background:
- Understanding the impact of thermal stress on human performance is crucial for optimizing exercise and occupational safety.
- Core and skin temperature modulate neuromuscular function, but their distinct effects on the force-EMG relationship require further elucidation.
Purpose of the Study:
- To investigate the independent effects of elevated core temperature (HOT-core) and skin temperature (HOT-skin) on the force and electromyography (EMG) relationship during plantarflexion.
- To quantify changes in maximal voluntary contraction (MVC) torque, voluntary activation (VA), and EMG amplitude under different thermal conditions.
Main Methods:
- Two studies were conducted: HOT-core (n=14) involved passive core temperature increase to 39°C in hot ambient conditions (46-50°C), and HOT-skin (n=11) involved local skin temperature manipulation in a temperate environment.
- Participants performed maximal voluntary contractions (MVC) of plantar flexors, with surface EMG recorded from soleus and gastrocnemius medialis. Tibial nerve stimulation determined voluntary activation (VA).
Main Results:
- HOT-core conditions led to significant reductions in MVC torque (-19%) and VA (-5%) compared to control (CON).
- HOT-skin conditions did not alter MVC torque (-1%) or VA (+0%).
- Both HOT-core (soleus -40%, GM -33%) and HOT-skin (soleus -10%, GM -13%) conditions resulted in decreased EMG activity (RMS) compared to CON.
Conclusions:
- Elevated core temperature impairs neuromuscular output, evidenced by reduced torque and activation.
- While skin temperature changes did not affect voluntary activation or torque, they did reduce EMG amplitude, suggesting potential methodological or physiological influences on EMG recordings.
- Hot ambient conditions alter the torque/EMG relationship, with torque decrements being less pronounced than EMG decrements during passive hyperthermia.
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