Increased temperature accelerates glycogen synthesis and delays fatigue in isolated mouse muscle during repeated...

Elevated glycogen content in muscle delays fatigue during exercise. We examined if increasing muscle temperature during recovery from exercise affects glycogen synthesis and muscle performance during a subsequent bout of exercise.

Isolated mouse extensor digitorum longus muscles were stimulated electrically to perform repeated tetanic contractions until force decreased to 40% of initial at 25°C. Thereafter, muscles recovered for 120 minutes at 25°C (control), 120 minutes at 35°C or 60 minutes at 35°C followed by 60 minutes at 25°C. After recovery, muscles were again stimulated to fatigue at 25°C.

In the control group, the number of contractions in the second run was slightly less than during the first run (92 ± 5%). Following recovery for 120 minutes at 35°C, the number of contractions was similar to the first run (98 ± 6%). Allowing recovery for 120 minutes at 35°C in the presence of the antioxidant N-acetylcysteine also did not alter the number of contractions in the second run (98 ± 3%). However, recovery for 60 minutes at 35°C followed by 60 minutes at 25°C resulted in an increase in the number of contractions during the second run (110 ± 2%, P < .001). Incorporation of [¹⁴ C]glucose into glycogen (glycogen synthesis) during recovery was 1.7-fold higher at 35°C vs 25°C (1.44 ± 0.08 μmol (30 min)^-1  (g wet muscle)^-1 vs 0.84 ± 0.04; P < .001).

These data demonstrate that, under the conditions studied, elevating muscle temperature for 60 minutes following a bout of repeated contractions delays muscle fatigue during a subsequent bout of repeated contractions and this is associated with enhanced glycogen synthesis in isolated muscle.