Learning to minimize energy costs and maximize mechanical work in a bimanual coordination task

The authors addressed the hypothesis that economy in motor coordination is a learning phenomenon realized by both reduced energy cost for a given workload and more external work at the same prepractice metabolic and attentional energy expenditure. "Self-optimization" of movement parameters has been proposed to reflect learned motor adaptations that minimize energy costs. Twelve men aged 22.3 [+ or -] 3.9 years practiced a 90[degrees] relative phase, upper limb, independent ergometer cycling task at 60 rpm, followed by a transfer test of unpracticed (45 and 75 rpm) and self-paced cadences. Performance in all conditions was initially unstable, inaccurate, and relatively high in both metabolic and attentional energy costs. With practice, coordinative stability increased, more work was performed for the same metabolic and attentional costs, and the same work was done at a reduced energy cost. Self-paced cycling was initially below the metabolically optimal, but following practice at 60 rpm was closer to optimal cadence. Given the many behavioral options of the motor system in meeting a variety of everyday movement task goals, optimal metabolic and attentional energy criteria may provide a solution to the problem of selecting the most adaptive coordination and control parameters.

Live high: train low increases muscle buffer capacity and submaximal cycling efficiency

This study investigated whether hypoxic exposure increased muscle buffer capacity (βm) and mechanical efficiency during exercise in male athletes. A control (CON, n=7) and a live high:train low group (LHTL, n=6) trained at near sea level (600 m), with the LHTL group sleeping for 23 nights in simulated moderate altitude (3000 m). Whole body oxygen consumption (V˙O₂) was measured under normoxia before, during and after 23 nights of sleeping in hypoxia, during cycle ergometry comprising 4×4-min submaximal stages, 2-min at 5.6 ± 0.4 W kg^–1, and 2-min 'all-out' to determine total work and V˙O_2peak. A vastus lateralis muscle biopsy was taken at rest and after a standardized 2-min 5.6 ± 0.4 W kg^–1 bout, before and after LHTL, and analysed for βm and metabolites. After LHTL, βm was increased (18%, P < 0.05). Although work was maintained, V˙O_2peak fell after LHTL (7%, P < 0.05). Submaximal V˙O₂ was reduced (4.4%, P < 0.05) and efficiency improved (0.8%, P < 0.05) after LHTL probably because of a shift in fuel utilization. This is the first study to show that hypoxic exposure, per se, increases muscle buffer capacity. Further, reduced V˙O₂ during normoxic exercise after LHTL suggests that improved exercise efficiency is a fundamental adaptation to LHTL.

Effects of starting strategy on 5-min cycling time-trial performance

The importance of pacing for middle-distance performance is well recognized, yet previous research has produced equivocal results. Twenty-six trained male cyclists ( V O_2peak 62.8+5.9 ml ·kg^-1 · min^-1· maximal aerobic power output 340+43 W; mean+s) performed three cycling time-trials where the total external work (102.7+13.7 kJ) for each trial was identical to the best of two 5-min habituation trials. Markers of aerobic and anaerobic metabolism were assessed in 12 participants. Power output during the first quarter of the time-trials was fixed to control external mechanical work done (25.7+3.4 kJ) and induce fast-, even-, and slow-starting strategies (60, 75, and 90 s, respectively). Finishing times for the fast-start time-trial (4:53+0:11 min:s) were shorter than for the even-start (5:04+0:11 min:s; 95% CI=5 to 18 s, effect size=0.65, P 50.001) and slow-start time-trial (5:09+0:11 min:s; 95% CI=7 to 24 s, effect size=1.00, P 50.001). Mean VO₂ during the fast-start trials (4.31+0.51 litres · min^-1) was 0.18+0.19 litres · min^-1 (95% CI=0.07 to 0.30 litres · min^-1, effect size=0.94, P =0.003) higher than the even- and 0.18+0.20 litres · min^-1 (95% CI=0.5 to 0.30 litres · min^-1, effect size=0.86, P =0.007) higher than the slow-start time-trial. Oxygen deficit was greatest during the first quarter of the fast-start trial but was lower than the even- and slow-start trials during the second quarter of the trial. Blood lactate and pH were similar between the three trials. In conclusion, performance during a 5-min cycling time-trial was improved with the adoption of a fast- rather than an even- or slow-starting strategy.