Passive heat acclimation improves skeletal muscle contractility in humans

Area of Science:

• Exercise Physiology
• Human Performance
• Environmental Physiology

Background:

• Muscle contractility is crucial for physical performance and daily activities.
• Understanding how environmental factors like heat affect muscle function is vital.
• Passive heat exposure is a potential method for physiological adaptation.

Purpose of the Study:

• To investigate the impact of repeated passive heat exposure (acclimation) on human skeletal muscle contractility.
• To assess changes in muscle function under both thermoneutral and hyperthermic conditions post-acclimation.

Main Methods:

• Fourteen non-heat-acclimated males underwent two trials (Cool and Hot) before and after 11 days of daily passive heat acclimation.
• Muscle contractility was measured using electrically evoked twitches and voluntary contractions.
• Core body temperature and sweat rate were monitored.

Main Results:

• Passive heat acclimation led to decreased core temperature in cool conditions and increased time to reach hyperthermia in hot conditions.
• Sweat rate significantly increased after acclimation.
• Skeletal muscle contractility improved, with significant increases in evoked peak twitch amplitude and maximal voluntary torque production in both cool and hot conditions.
• The relationship between torque and electromyography improved, indicating enhanced muscle activation efficiency.

Conclusions:

• Passive heat acclimation enhances skeletal muscle contractile function during both electrically evoked and voluntary contractions.
• These improvements in muscle function are observed in both cool and hot environments.
• Repeated heat exposure offers a viable strategy to maintain or improve muscle function in diverse performance and clinical contexts.