Time of day effects on repeated sprint ability

Area of Science:

• Sports Science
• Human Physiology
• Exercise Physiology

Background:

• Diurnal variations in physiological functions can impact athletic performance.
• Understanding time-of-day effects on muscle power and fatigue is crucial for optimizing training and competition strategies.

Purpose of the Study:

• To investigate the impact of time-of-day (morning vs. evening) on muscle power output and electromyographic (EMG) activity during repeated pedaling sprint exercise.
• To determine if diurnal variations affect neuromuscular efficiency and fatigue during intense, short-duration exercise.

Main Methods:

• 12 male subjects performed a repeated sprint ability test at 06:00 h and 18:00 h in a randomized order.
• Peak power output, peak power decrement, and total work were calculated for each sprint.
• Electromyographic (EMG) activity of vastus lateralis, rectus femoris, vastus medialis, and biceps femoris muscles was recorded and analyzed.

Main Results:

• Total work and percentage of peak power decrement were significantly higher in the evening.
• Peak power output was significantly greater in the evening compared to the morning for the initial sprints.
• No significant time-of-day effect was observed for the EMG activity level of the tested thigh muscles.

Conclusions:

• Muscle power output and fatigue characteristics during repeated sprint exercise exhibit diurnal variations, with superior performance in the evening.
• Despite fluctuations in power output and fatigue, the underlying neuromuscular activation patterns, as measured by EMG, do not appear to be time-of-day dependent.
• Neuromuscular efficiency significantly decreases over the course of the repeated sprint test, irrespective of the time of day.