The politics of race in the Midwest, 1864--1890.

The politics of race in the Midwest, 1864--1890

The adaptation to standing long jump distance in parkour is performed by the modulation of specific variables prior and during take-off

The present study aimed at investigating different variables that can be manipulated prior to and during take-off, to execute a specific standing long jump (SLJ) distance, according to jump expertise in parkour practitioners (= traceurs). Fourteen healthy young traceurs were included and separated into two groups: beginners (BEG) and experts (EXP). Firstly, classical vertical jump battery was used to characterize participants arm use and leg efficiency. Secondly, standing long jump (SLJ) performances were analyzed at four distances: 70, 80, 90, and 100% of each participant’s maximal SLJ distance. The force-time curves of the ground reaction forces (GRF) and the center of pressure (CoP) trajectory were measured with a force platform during the jump impulses. Take-off speed, angle and jump trajectory were estimated. For all of the participants, take-off speed and angle, power output, and vertical GRF during jump preparation (counter movement) varied with distance. The EXP group exhibited greater backward CoP excursion, greater arm participation, greater take-off velocity and a greater modulation of take-off angle than BEG group. When comparing jumps of similar distance, EXP exhibited a more curvilinear trajectory with a higher peak than BEG. To conclude, different motor strategies can be adopted based on the jump distance, and these strategies can evolve as parkour experience increases

Muscle force recovery in relation to muscle oxygenation

International audienceThe aim of this study was to investigate the relative contribution of human muscle reoxygenation on force recovery following a maximal voluntary contraction (MVC). Ten athletes (22·9 ± 4·0 years) executed a plantar-flexion sequence including two repeated MVCs [i.e. a 30-s MVC (MVC(30)) followed by a 10-s MVC (MVC(10))] separated by 10, 30, 60, 120 or 300 s of passive recovery. A 10-min passive recovery period was allowed between each MVC sequence. This procedure was randomly repeated with two different recovery conditions: without (CON) or with (OCC) arterial occlusion of the medial gastrocnemius. During OCC, the occlusion was maintained from the end of MVC(30) to the end of MVC(10). Muscle oxygenation (Near-infrared spectroscopy, NIRS, [Hb(diff) ]) was continuously measured during all MVC sequences and expressed as a percentage of the maximal changes in optical density observed during MVC(30). Maximal Torque was analysed at the start of each contraction. Torque during each MVC(10) was expressed as a percentage of the Torque during the previous MVC(30). Torque recovery was complete within 300 s after MVC(30) during CON (MVC(10) = 101·8 ± 5·0%); 88·6 ± 8·9% of the Torque was recovered during OCC (P = 0·005). There was also a moderate correlation between absolute level of muscle oxygenation and Torque (r = 0·32 (90% CI, 0·09;0·52), P = 0·02). Present findings confirm the role of human muscle oxygenation in muscular force recovery during repeated-maximal efforts. However, the correlation between absolute muscle oxygenation and force level during recovery is only moderate, suggesting that other mechanisms are likely involved in the force recovery process