Effects of endurance training on performance and metabolism during a repeated treadmill sprint in females

A small number of previous cross-sectional studies have examined the relationship between endurance training status on recovery of performance and metabolites from sprinting. However, no longitudinal studies have been undertaken. In addition, there is a dearth of information on female subjects and on running exercise which prompted the need, in the present thesis, to address the effect of menstrual cycle phase on performance and metabolic responses during a repeated sprint run. Thus, the overall purpose of the present thesis was to examine the effect of short-term endurance training on a repeated sprint in female subjects. A number of methodological studies (for which 25 subjects volunteered) were undertaken as preparation for the main experimental chapters of the thesis (Chapter 3). The first methodological study examined the reliability of performance during a 30-s sprint on the non-motorised treadmill. Performance was reproducible as indicated by the 95 % limits of agreement for PPO (5 ± 42 W) and by the ratio limits of agreement for MPO (1.01 */+1.06) during the 30 s sprint. In the second methodological study it was found that capillary lactate concentrations were significantly higher than venous blood lactate after a 30 s sprint (P < 0.05). The third methodological study revealed that a repeated sprint run caused an additional plasma volume loss when compared with the loss caused by a change in posture alone (12.7 % vs 7.5 % for sprint and posture change, respectively, P < 0.05). Finally, it seems that prolonged freezing (up to 13 months) does not have a detrimental influence on whole blood lactate concentration, but repeated defrosting may result in errors in the determination of blood lactate at high lactate concentrations (methodological study 4). The first mam experiment examined the effects of menstrual cycle phase on performance and metabolic responses during a repeated sprint run (2x30 s, with a 2 min passive recovery) in 8 volunteers (chapter 4). Performance was unaltered during the follicular, mid-cycle and luteal phase of the menstrual cycle as reflected by PPO (461 ± 51 and 395 ± 48, 443 ± 43 and 359 ± 44, 449 ± 52 and 397 ± 48 W, for the first and second sprint, during the follicular, mid-cycle and luteal phase, respectively, P> 0.05) and MPO (302 ± 41 and 252 ± 29,298 ± 37 and 248 ± 29,298 ± 39 and 252± 35 W, for the first and second sprint, at follicular, mid-cycle and luteal phases, respectively, P > 0.05). Similarly, blood metabolic responses were unaffected by menstrual cycle phase as reflected by the unchanged metabolic profile of blood lactate, plasma' ammonia, blood pH and % changes in plasma volume across menstrual cycle. These results suggest that the hormonal fluctuations of 17-,B-estradiol (estradiol) and progesterone, due to menstrual cycle phase, have no effect on repeated sprint performance and possibly on the metabolic responses as reflected by the blood metabolic responses. The second main experiment examined the effects of short-term endurance training on power output recovery and metabolic responses to a repeated sprint run (2x30 s with a 2 min passive recovery) (chapter 5, n = 16). Six weeks of endurance training resulted in a 3 % increase (P < 0.05) in V 02 max (from 48.7 ± 4.4 before training to 50.17 ± 5.1 mL.kg-1·min-1 after training) in the training group (n = 8) in comparison with 1.9 % decrease (from 50.4 ± 1.3 to 49.4 ± 1.2 mL.kg-1·min-1 post-trial) in the control group (n = 7). In addition, % V O2 max @ 4 mmoz·r1 [the relative intensity (% V O2 max) corresponding to blood lactate concentration of 4 mmol·L-1] was 3 % higher (from 82 to 84 %) in the training group as compared with the 1 % decrease in the control group (from 81 to 80 %) (P < 0.05). These endurance adaptations were accompanied by a 7 % improvement in MPO recovery (in the second of two 30 s sprints) in the training group in comparison with 2 % increases in the control group after training (P < 0.05). Metabolic responses to sprints were unaltered after training, but there was a tendency for higher pH immediately after sprint 1 in the training group in comparison with the control group (7.12 ± 0.07 vs 7.19 ± 0.06 and 7.09 ± 0.07 vs 7.10 ±0.06, before and after training, in the training and control group, respectively, P = 0.082). These findings suggest that endurance training can be beneficial in terms of quicker recovery of performance during a repeated sprint run. The third main experiment examined the effects of endurance training on performance recovery and muscle metabolites (chapter 6, n=14). Endurance training resulted in a tendency towards lower blood lactate concentrations during sub-maximal exercise in the training group in comparison with the control group (P = 0.063) whilst time to exhaustion for the incremental V O2 max test was 12.7 % longer for the training group in comparison with 4.1 % decrease in the control group (P = 0.095). These endurance training adaptations were accompanied by a 7 % improvement (77 ± 7 to 84 ± 5 W) in MPO recovery in the second of two 30 s sprints in the training group while in the control group MPO recovery improved by just 2 % (87 ± 8 to 89 ± 8 %) (P < 0.05). In addition, similar increases in the recovery of peak speed (3.4 % vs 1 %, P < 0.05), and mean speed (5 % vs 0.9 %, P < 0.05) were also evident in the training in comparison with control group. Endurance training resulted in 5.6 % decrease in ATP provision from PCr degradation ~ 14 s post-sprint 1 (P < 0.05) while glycogen degradation was 10 % lower (P = 0.063). The latter alterations, in turn, resulted in a tendency towards less reliance on anaerobic energy resources for energy supply after training in the training group (11 %, P = 0.098). These results corroborate the findings of chapter 5, but it is still unclear which physiological mechanisms were instrumental in enhancing recovery of performance. It is possible that a faster initial PCr resynthesis or an improved mechanical efficiency or an increased reliance on aerobic metabolism, independently, all together, or in any combination, could have contributed to these improvements in performance recovery. In conclusion the present thesis has shown that: the non-motorised treadmill is a reliable tool for the examination of sprint running performance in the laboratory; that performance and metabolic responses during a repeated sprint run are unaffected by menstrual cycle phase and; that endurance training enhances the recovery of power in female subjects during a repeated sprint run of 2 x 30 s duration with a 2 min passive recovery. The mechanisms underlying the performance improvement following endurance training are unknown, but it is possible that faster PCr resynthesis during the initial phase of recovery «1 min) after the sprint is the dominant factor, while greater reliance on aerobic metabolism and improved mechanical efficiency can not be excluded.