Andrew J. Cathcart

Effect of 2 weeks of sprint interval training on health-related outcomes in sedentary overweight/obese men

The aim of this study was to investigate the effects of very high intensity sprint interval training (SIT) on metabolic and vascular risk factors in overweight/obese sedentary men. Ten men (age, 32.1 ± 8.7 years; body mass index, 31.0 ± 3.7 kg m(-2)) participated. After baseline metabolic, anthropometric, and fitness measurements, participants completed a 2-week SIT intervention, comprising 6 sessions of 4 to 6 repeats of 30-second Wingate anaerobic sprints on an electromagnetically braked cycle ergometer, with 4.5-minute recovery between each repetition. Metabolic, anthropometric, and fitness assessments were repeated post-intervention. Both maximal oxygen uptake (2.98 ± 0.15 vs 3.23 ± 0.14 L min(-1), P = .013) and mean Wingate power (579 ± 24 vs 600 ± 19 W, P = .040) significantly increased after 2 weeks of SIT. Insulin sensitivity index (5.35 ± 0.72 vs 4.34 ± 0.72, P = .027) and resting fat oxidation rate in the fasted state (0.13 ± 0.01 vs 0.11 ± 0.01 g min(-1), P = .019) were significantly higher and systolic blood pressure (121 ± 3 vs 127 ± 3 mm Hg, P = .020) and resting carbohydrate oxidation in the fasted state (0.03 ± 0.01 vs 0.08 ± 0.02 g min(-1), P = .037) were significantly lower 24 hours post-intervention compared with baseline, but these changes were no longer significant 72 hours post-intervention. Significant decreases in waist (98.9 ± 3.1 vs 101.3 ± 2.7 cm, P = .004) and hip (109.8 ± 2.2 vs 110.9 ± 2.2 cm, P = .017) circumferences compared with baseline were also observed after the intervention. Thus, 2 weeks of SIT substantially improved a number of metabolic and vascular risk factors in overweight/obese sedentary men, highlighting the potential for this to provide an alternative exercise model for the improvement of vascular and metabolic health in this population.

Control strategies for integration of electric motor assist and functional electrical stimulation in paraplegic cycling: utility for exercise testing and mobile cycling

Aim: The aim of this study was to investigate feedback control strategies for integration of electric motor assist and functional electrical stimulation (FES) for paraplegic cycling, with particular focus on development of a testbed for exercise testing in FES cycling, in which both cycling cadence and workrate are simultaneously well controlled and contemporary physiological measures of exercise performance derived. A second aim was to investigate the possible benefits of the approach for mobile, recreational cycling. Methods: A recumbent tricycle with an auxiliary electric motor is used, which is adapted for paraplegic users, and instrumented for stimulation control. We propose a novel integrated control strategy which simultaneously provides feedback control of leg power output (via automatic adjustment of stimulation intensity) and cycling cadence (via electric motor control). Both loops are designed using system identification and analytical (model-based) feedback design methods. Ventilatory and pulmonary gas exchange response profiles are derived using a portable system for real-time breath-by-breath acquisition. Results: We provide indicative results from one paraplegic subject in which a series of feedback-control tests illustrate accurate control of cycling cadence, leg power control, and external disturbance rejection. We also provide physiological response profiles from a submaximal exercise step test and a maximal incremental exercise test, as facilitated by the control strategy. Conclusion: The integrated control strategy is effective in facilitating exercise testing under conditions of well-controlled cadence and power output. Our control approach significantly extends the achievable workrate range and enhances exercise-test sensitivity for FES cycling, thus allowing a more stringent characterization of physiological response profiles and estimation of key parameters of aerobic function. We further conclude that the control approach can significantly improve the overall performance of mobile recreational cycling.

Ventilatory control during intermittent high-intensity exercise in humans.

Intermittent supra-maximal cycling of varying work: recovery durations was used to explore the kinetics of respiratory compensation for the metabolic acidosis of high-intensity exercise (> lactate threshold, thetaL). For a 10:20s duty-cycle, blood [lactate] ([L-]) was not increased, and there was no evidence of respiratory compensation (RC); i.e, no increase in the ventilation (VE)-CO2 output (Vco2) slope, nor fall in end-tidal PCO2 (PETCO2). For longer duty-cycles, [L-] was elevated, stabilizing (30s:60 s exercise) or rising progressively (60s:120s, 90s: 180s exercise). In addition, Vco2 and VE now oscillated with WR, with evidence of delayed RC (progressive increase in VE - VCO2 slope; decrease in PETCO2) being more marked with longer duty-cycles. These results, which extend earlier findings with supra- thetaL step and ramp exercise, are not consistent with an appreciable contribution to RC from zero-order central command or peripheral neurogenesis. The reasons for the slow RC kinetics are unclear, but may reflect in part the H(+)-signal transduction properties of carotid chemoreceptors.