1 Det Sundhedsvidenskabelige Fakultet, SDU2 Department of Sports Science and Clinical Biomechanics, Det Sundhedsvidenskabelige Fakultet, SDU3 Muscle Physiology and Biomechanics, Department of Sports Science and Clinical Biomechanics, Det Sundhedsvidenskabelige Fakultet, SDU4 Copenhagen Muscle research centre5 Mittuniversitetet, Østersund, Sweden6 Department of Sports Science and Clinical Biomechanics, Det Sundhedsvidenskabelige Fakultet, SDU
INTRODUCTION: In skeletal muscle, glucose is stored as glycogen, which is a major source of energy during most forms of muscle activity. It is now well recognized that muscle glycogen stores are closely related to performance and endurance capacity. Thus, successful competition or training depends on an optimal glycogen resynthesis rate before a subsequent exercise session. The purpose of present study was to evaluate the glycogen resynthesis rate in elite cross-country (cc) skiers, following exhaustive exercise, and to examine the role of muscular glycogen content on the resynthesis rate. METHOD: Ten male elite cc skiers (age: 22 ± 0.4 years; height: 181 ± 2 cm; body mass: 78.8 ± 2.6 kg) with a VO2 max of 72 ± 2 [range 62-79] ml . kg-1 . min-1 (5.4 ± 0.5 [range 4.8-6.1] L . min-1) and 700 training hours per year [550 – 850]) volunteered for the study. The skiers performed a ~20 km time-trial (classic style) on a competition cc track. During the first 4hrs of recovery, skiers received either water or carbohydrate (CHO), after which they all received CHO enriched food (1 g . kg-1 bw . h-1). Muscle biopsies were obtained in both arm and leg muscles before and immediately after the race, as well as 4h and 22h after the race and analyzed for glycogen content. Figure 1. Correlation between muscle glycogen resynthesis rate and glycogen content after and in the rocery period after exercise. Line indicate best fit of all the data points (r2 = 0.41, p<0.01). RESULTS: The average race time for the ~20 km race was 57 ± 1 min [52– 62 min]. On average, muscle glycogen was reduced to 31 ± 4% (from 540 to 167 mmol . kg-1 dw) in the arms and 71 ± 10% (from 485 to 331 mmol . kg-1 dw) in the legs directly after the race. After 4h recovery with CHO, arm glycogen was noticeably recovered (59 ± 5% of Pre) and was fully recovered in the leg muscle. In the absence of CHO during the first 4h recovery, muscle glycogen remained low. However, after the remaining 18h of recovery with CHO the muscle glycogen was restored to pre-race levels in both the CHO and water trials. The glycogen resynthesis rate was, on average, 29±7 (arm CHO) and 13±7 (leg, CHO) mmol . kg-1 dw . h-1, for the first 4h recovery, and from 4-22h resynthesis rates were 13±4 (arm, CHO), 14±3 (arm, water first 4h), 5±2 (leg, CHO), and 12±7 (leg, water first 4h). There was a clear correlation between muscle glycogen content and resynthesis rate in the recovery period. DISCUSSION: Here we demonstrate that elite cc skiers´ glycogen resynthesis is correlated to muscle glycogen, resulting in a faster rate of glycogen resynthesis in the early post-exercise period. However, this is also evident after keeping muscle glycogen low in the initial recovery period, leading to a similar muscle glycogen content following 22h of recovery after a depleting race. CONCLUSION: In elite trained cc-skiers, muscle glycogen stores are fully re-synthesized 22h after an exhaustive race, when providing sufficient CHO intake. This is also evident regardless of omitting CHO for the first 4h recovery. Furthermore, these data strongly indicate a close correlation between muscle glycogen content and resynthesis rate.
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5th International Congress on Science and Skiing, 2010