The hyperbolic relationship between power output and endurance time can be measured using all-out exercise. The aims of this thesis were to (i) assess whether the all-out test could be used under novel testing protocols to provide valid power-duration (P-D) parameter estimates; and (ii) attempt to elucidate the likely physiological composition of the P-D curvature constant. All-out tests were initiated from moderate-(M), heavy-(H) and severe-(S2 & S4) intensity ‘baselines’ (chapter 4). The work performed above end power (WEP) was not different to control under M or H conditions but was significantly, predictably reduced under the S2 & S4 conditions (control: 16.3 ± 2.2; M: 17.2 ± 2.4; H: 15.6 ± 2.3 kJ, P > 0.05; S2: 11.5 ± 2.5; S4: 8.9 ± 2.2 kJ, P < 0.05). The 3-min all-out test end power (EP) parameter was unaffected. Muscle glycogen may form part of the WEP. Type I (T1) and type II (T2) muscle fibres were depleted of their glycogen content prior to the all-out test (chapter 5). EP and WEP were unaffected by either T1 or T2 glycogen depletion. The all-out tests was conducted under hypoxic conditions alongside the criterion assessment of the P-D relationship (chapter 6). Normobaric moderate hypoxia caused a reduction in CP (control: 175 ± 25; hypoxia: 132 ± 17 W, P < 0.001) without affecting W′ (control: 13.2 ± 2.2; hypoxia: 12.3 ± 2.7 kJ, P > 0.05). The 3-min all-out test provided EP and WEP estimates, which did not differ to CP and W′ (control: EP 172 ± 30 W, WEP 12.0 ± 2.6 kJ; hypoxia EP 134 ± 23 W, WEP 12.5 ± 1.4 kJ, P > 0.05) providing the ergometer resistance was adjusted for the hypoxic conditions. Furthermore, a significant negative relationship was observed between %∆ ( O2peak – CP) and %∆W′ (r = -0.83, P < 0.001); thus, W′ may represent the relative ‘size’ of the severe-intensity domain. The all-out test was used to track training-induced changes in P-D parameters in response to 6-weeks of sprint or endurance training (chapter 7). EP & WEP were differently altered compared to CP and W′ following sprint training (CP 12 ± 9; EP -0 ± 9 % change; W′ -5 ± 25; WEP 11 ± 15 % change). The all-out test reliably tracked changes in CP and W′ following endurance training. In conclusion, the all-out test provides reliable EP and WEP values. Its validity is acceptable, but is perhaps affected by exercise training that is specific to the execution of the test. The W′ appears to be determined, to a large extent, by the relative size of the severe-intensity domain.

Critical Power (CP) is the greatest power that a person can sustain for prolonged periods of time while maintaining steady state conditions. Work-prime (W’) is the amount of work that can be tolerated when exercising in non-steady-state conditions above CP. A person’s CP and W’ strongly influence the metabolic response and tolerance to exercise. PURPOSE: Compare the effect of equal amounts of moderate intensity continuous training (MICT) and high intensity interval training (HIIT) on CP and W’. Critical Power (CP) is the greatest power that a person can sustain for prolonged periods of time while maintaining steady state conditions. Work-prime (W’) is the amount of work that can be tolerated when exercising in non-steady-state conditions above CP. A person’s CP and W’ strongly influence the metabolic response and tolerance to exercise. PURPOSE: Compare the effect of equal amounts of moderate intensity continuous training (MICT) and high intensity interval training (HIIT) on CP and W’. METHODS: Twenty-two (10 female) untrained, young (26.4 ± 0.9 years) adults completed 8 weeks of cycling training (40 min, 3  per week) administered as either MICT cycling (44% max work rate achieved during a maximal graded exercise test; GXTmax) or HITT cycling (4 bouts at 80% GXTmax for 4 min with recovery intervals between). Cycling V̇O2max, CP, W’ and Anaerobic Capacity (i.e., Wingate) were determined before and after training. Specifically, CP was assessed with the work-over-time method derived from 4–5 constant-power tests to exhaustion. RESULTS: MICT (n = 11) and HIIT (n = 11) groups completed the same amount of work over the course of the training (P = 0.76). CP significantly increased in both groups, but to a greater extent in the HIIT group (MICT: 15.7 ± 3.1% vs. HIIT: 27.5 ± 4.3%; P = 0.04). The work that could be performed above CP (i.e., W’) was not significantly impacted by training (p = 0.76). V̇O2max significantly increased in both groups (P < 0.01), and the magnitude tended to be greater in the HIIT group (MICT: 8.3 ± 2% vs. HIIT: 14 ± 2.6%; P = 0.09). Interestingly, the training-induced change in CP was not significantly related to the training-induced change in V̇O2max. The training-induced increase in CP exhibited a positive curvilinear relationship with the training intensity, expressed as a percentage of the initial CP, with those performing the same workout at a greater percentage of CP exhibiting greater training-induced increases in CP (R2 = 0.49, P < 0.01). CONCLUSION: HIIT elicits approximately twice the increase in CP than an equal amount of MICT in untrained young adults. Moreover, the magnitude of increase in CP is strongly related to the intensity of the exercise, relative to CP, even when exercising at the same percentage of GXTmax. Thus, exercise may be more effectively prescribed relative to CP, rather than V̇O2max or GXTmax.

PURPOSE: To investigate the effect of the menstrual cycle (MC) on exercise performance across the power-duration relationship (PDR). We hypothesized females would exhibit greater variability in the PDR across the MC than males across a similar timespan, with critical power (PCRIT) and Work prime (W') being lower during the early follicular phase than the late follicular and mid-luteal phases. METHODS: Eumenorrheic, endurance-trained females (n = 10, age = 24.1 ± 5.59) performed multiple constant-load-to-task-failure and maximum-power tests at three time points across the MC (early follicular, late follicular, midluteal phases). Endurance-trained males (n = 10 age = 29.5 ± 9.18) performed the same tests approximately 10 days apart to mimic the time between the phases of the MC. RESULTS: No differences across the PDR were observed between MC phases (PCRIT: 175.66 ± 34.97 W, P = 0.632, CV = 1.28 ± 0.97 %) (W': 7916.53 ± 2316.69 J, P = 0.283, CV = 13.56 ± 6.93 %). PCRIT was similar for males and females (11.82 ± 1.44 W • kg-1 vs. 11.20 ± 1.82 W • kg?1, respectively) when controlling for leg lean mass. However, W' was larger (P = 0.048) for males (617.28 ± 130.10 J • kg?1) than females (505.24 ± 137.66 J • kg?1). CONCLUSION: These findings indicate that researchers do not need to account for MC phase when conducting performance research on female subjects. Nevertheless, factors, such as body size and leg lean body mass, do limit exercise performance in males and females. As such, previous studies looking at factors limiting exercise performance in males may not always apply to females.