PURPOSE: The aim of the present study was to investigate the influence of muscle glycogen content on sarcoplasmic reticulum (SR) function and peak power output (Wpeak) in elite endurance athletes.
METHODS: Fourteen highly trained male triathletes (VO2max 66.5 ± 1.3 ml O2 kg min), performed 4h of glycogen depleting cycling exercise (HRmean 73 ± 1% of maximum). During the first 4h recovery, athletes received either water (H2O) or carbohydrate (CHO), separating alterations in muscle glycogen content from acute changes affecting SR function and performance. Thereafter, all subjects received CHO enriched food for the remaining 20h recovery.
RESULTS: Immediately following exercise, muscle glycogen content and SR Ca release rate was reduced to 32 ± 4% (225 ± 28 mmol kg dw) and 86 ± 2% of initial levels, respectively (P < 0.01). Glycogen markedly recovered after 4h recovery with CHO (61 ± 2% of pre) and SR Ca release rate returned to pre-exercise level. However, in the absence of CHO during the first 4h recovery, glycogen and SR Ca release rate remained depressed, with normalization of both parameters at the end of the 24h recovery after receiving a CHO enriched diet. Linear regression demonstrated a significant correlation between SR Ca release rate and muscle glycogen content (P < 0.01, r = 0.30). The 4h cycling exercise reduced Wpeak by 5.5-8.9% at different cadences (P < 0.05) and Wpeak was normalized after 4h recovery with CHO whereas Wpeak remained depressed (P < 0.05) following water provision. Wpeak was fully recovered after 24h in both the H2O and the CHO group.
CONCLUSION: In conclusion, the present results suggest that low muscle glycogen depresses muscle SR Ca release rate, which may contribute to fatigue and delayed recovery of Wpeak 4 hours post exercise.
2014. Vol. 46, no 3, 496-505 p.