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All exercise draws first on intramuscular stores of ATP and creatine phosphate; initially these are replenished by anaerobic glycolysis. The lactic acid produced contributes to the rapid development of fatigue in high intensity exercise. Aerobic metabolism (at first mainly of glycogen, later increasingly of fat) is the principal route of ATP resynthesis in activities lasting longer than 2 min, but can only maintain work-rates about 1/4 of those possible in very brief bursts. Blood lactate rises at the higher aerobic work rates. 'Lactate threshold' (LT: approximately 2 mmol/l) is almost exactly the speed at which endurance races are won, and close to those apparently providing optimal aerobic training. This training, predominantly of muscle aerobic capacity, elevates LT more than maximum oxygen consumption. LT is not now thought to indicate oxygen-deprivation, but intracellular adjustments driving oxidative phosphorylation faster. Ventilatory breakpoints, formerly considered to indicate LT, correlate more closely with the accumulation of potassium than lactate.

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Ten male and ten female young adults trained the knee extensors of one leg eccentrically and those of the other concentrically for 6 weeks, using a gymnasium leg-extension machine. Before and after training, both legs of each subject were tested isometrically for maximum voluntary knee-extensor force, and in both eccentric and concentric isokinetic modes at 30-250 degrees x s(-1) All limbs showed improvements in mean eccentric force (ranging from 18% in the concentrically trained legs of the females to 31% in the eccentrically trained legs of the males, P < 0.01-0.001). Upward trends in isometric and concentric forces were smaller and less- or nonsignificant. In three of the four groups, mean eccentric forces after training were significantly greater than mean isometric forces, a difference that was not evident before training. Ten further subjects of each gender, not trained but tested isometrically and isokinetically three times in 2 weeks, showed no significant improvement over the series of tests. The explanation suggested is that the increased percentage activation ("decreased inhibition"), often regarded as the main mechanism of strength gain in the early weeks of training, had been displayed particularly in the subjects' eccentric performance. This implies that the activation-shortfall, which is reduced by the initial phase of strength training, is largely or completely the same as that responsible for the fact that untrained, voluntary eccentric force is less than that of isolated muscle.

Laser class sailors have to hike out, i.e. hook their feet under the toe straps near the centreline of the boat and hold their upper bodies over the edge of the boat, to counteract the heeling forces generated by the sails. To identify the parameters that are associated with maximal hiking performance, this cross-sectional observational study measures various knee extensor and hip flexor muscle performance characteristics in 55 Laser sailors and correlates each with the area-under-the-curve hiking moment over 3 min of hiking on a hiking dynamometer (HM180). Our results showed that higher body mass and HM180 were significantly associated with better race scores (Spearman's rho = - 0.69 and - 0.62, respectively, both P < 0.01) in male sailors who participated in the National Inter-School Laser competition. Body mass (Pearson's correlation coefficient, r > or = 0.95, P < 0.01 in both males and females), maximum voluntary isometric strength of the quadriceps (r > or = 0.80, P < 0.01 in both males and females), and 3-RM knee extension strength (r > or = 0.80, P < 0.01 in both males and females) were associated with a higher HM180. The correlations between height, abdominal muscle endurance (crunches), explosive lower body strength (vertical jumps), cycling time-to-exhaustion, quadriceps strength endurance, or isometric quadriceps endurance with incremental loads (bucket test), and HM180 were weaker (r < 0.60). HM180 may be a useful performance indicator for Laser racing. Since strength measures correlated well with HM180, greater emphasis should be placed on developing maximum strength in the quadriceps to improve maximal hiking performance.