Strength Training for Middle- and Long-Distance Performance: A Meta-Analysis

Purpose: To assess the net effects of strength training on middle- and long-distance performance through a meta-analysis of the available literature. Methods: Three databases were searched, from which 28 of 554 potential studies met all inclusion criteria. Standardized mean differences (SMDs) were calculated and weighted by the inverse of variance to calculate an overall effect and its 95% confidence interval (CI). Subgroup analyses were conducted to determine whether the strength-training intensity, duration, and frequency and population performance level, age, sex, and sport were outcomes that might influence the magnitude of the effect. Results: The implementation of a strength-training mesocycle in running, cycling, cross-country skiing, and swimming was associated with moderate improvements in middle- and long-distance performance (net SMD [95%CI] = 0.52 [0.33–0.70]). These results were associated with improvements in the energy cost of locomotion (0.65 [0.32–0.98]), maximal force (0.99 [0.80–1.18]), and maximal power (0.50 [0.34–0.67]). Maximal-force training led to greater improvements than other intensities. Subgroup analyses also revealed that beneficial effects on performance were consistent irrespective of the athletes’ level. Conclusion: Taken together, these results provide a framework that supports the implementation of strength training in addition to traditional sport-specific training to improve middle- and long-distance performance, mainly through improvements in the energy cost of locomotion, maximal power, and maximal strength.

Energy Efficiency of Legged Robot Locomotion With Elastically-Suspended Loads Over a Range of Suspension Stiffnesses

Elastically suspending a load from humans and animals can increase the energy efficiency of legged locomotion and load carrying. Similarly, elastically-suspended loads have the potential to increase the energy efficiency of legged robot locomotion. External loads and the inherent mass of a legged robot, such as batteries, electronics, and fuel, can be elastically-suspended from the robot chassis with a passive compliant suspension system, reducing the energetic cost of locomotion. In prior work, we developed a simple model to examine the effect of elastically-suspended loads on the energy cost of locomotion from first principles. In this paper, we present experimental results showing the energy cost of locomotion for a simple hexapod robot over a range of suspension stiffness values. Elastically-suspended loads were shown to reduce the energy cost of locomotion by up to 20% versus a rigidly-attached load. We compare the experimental results to the theoretical results predicted by the simple model.

Factors Contributing to the Energy Expenditure of Youth during Cycling and Running

This study evaluated factors that contribute to the increased energy cost of locomotion in youth. The subjects were 321 8-18-year-old youth, similar dispersed by age and sex. Oxygen uptake (VO2) was measured during rest (REE), running at 8 km · h−1 and cycling at 16 km · h−1, using a COSMED K4b2 metabolic system. Developmental stage was obtained via questionnaire. Stature, body mass, and skinfolds (triceps & subscapular) were measured. Both sexes had similar absolute VO2 (mL · min−1) at rest (p = 0.065) and running (p = 0.084), but the males had a higher VO2 during cycling (p = 0.046). There were no sex differences in relative VO2 (mL · kg−1 · min−1) at rest (p = 0.083); however, the males had a higher VO2 than the females during cycling and running (p £ 0.002). Multiple regression, tested for collinearity, found that absolute VO2 during cycling and running was mostly related to fat-free mass (p = 0.0001). Similar analyses for relative VO2 (mL · kg−1 · min−1) during cycling found that fat-free mass, sex, and skinfolds were significant contributors (p ‡ 0.003). During running the relative VO2 was related to skinfolds, fat-free mass, and resting energy expenditure (p < 0.05). Neither age nor developmental stage was a significant contributor. The results indicate that the VO2 of locomotion is most closely associated with fat-free mass. Thus, to compare youth of varying age or pubertal developmental status, fat-free mass should be taken into consideration.