![]() The testing session included three tests to evaluate Es, Rs and SSE according to Bosco (1994) in the following sequence: three attempts of a counter movement jump (CMJ), with a two minutes rest between attempts, where the best performance was recorded after a three minutes rest, a stiffness test that included 15 reactivity jumps (15React) after a four to five minutes rest a 30 seconds continuous CMJ (30CMJ). The subjects were instructed not to engage in high-intensity training during the 48 hours prior to the testing session. Before the experiments, the subjects were familiarised with the testing procedures. ProceduresĪll subjects were evaluated at the end of the Preparatory Phase for three consecutive sea- sons. The athletes were assigned in two groups according to their performance level. The main aims of the present study were to identify differences in Es, Rs and SSE, between two groups of 400m runners with distinct performance levels and to identify associations between each strength component and 400m performance (t400) in speed endurance athletes.įifteen elite male runners, 400m and 400m hurdle specialists, volunteered to participate in the present study, after being informed about the aims, risks and advantages of their participation. However, we have found no data on differences of the strength levels in 400m runners from distinct performance levels. Until the present time, several studies with distinct populations have been performed in order to investigate the strength components and their importance in sprint events (Num- mela et all, 1992 Delecluse, 1997 Locatelli, 1996 Manou et all, 2000 Chelly & Denis, 2001 Henessy & Kilty, 2001 Miguel, 2003). explosive strength (Es), reactive strength (Rs) and especially Es endurance or speed strength endurance (SSE). Therefore, SE seems to be a determinant factor in 400m performance and athletes with the best performances in the event should also be able to express more power in sprint specific strength components, i.e. The greater the ability of the athlete to oppose fatigue (by maintaining strength levels), the smaller the drop in speed and consequently the better the performance (Harre & Leopold, 1987). 1994), strength endurance (SE) will prevail as the determinant of success in this event. 1990) or to FT fibers failure (Nummela et al. 1992), due to metabolic changes (Arcelli, 1995 Lacour et al. ![]() Indeed, once the strength capacity progressively decreases during the event (Nummela et al. ![]() ![]() This possible failure in stiffness characteristics may reduce the storage of elastic energy during the braking phase. The differences found by the authors between a sub-maximal 20m run at competition pace and the end of the 400m run suggests possible changes in stiffness regulation. In the same study, the authors have found that during the last phase of the event, ground reaction forces decreased remarkably during the braking phase, which implies that the musculotendon system reduced capacity to tolerate impact forces. This increase in EMG activity during the 400m is caused by the increase in the firing rate and/or the recruitment of additional motor units to compensate for failure in contractile capacity of muscle fibers that have already been recruited (Nummela et al. Additionally, it is possible to observe an increase of the electromyographic record (EMG) of the muscles that participate in the sprinting action. However from the 200- 300m onwards there is a strength reduction, as capillary lactates concentration attains more than 6mmol/l, and the pH drops. (1994) suggest that during the first 200m of the race muscle properties are modified (reflected by an increase of contact time and a decrease of explosive strength in the height of jump) even without a decrease in the running speed. These results and the results from Nummela et al. Moreover, the authors found a linear negative relationship between jump height and lactate levels above 6mmol/l. After the 300m there was a 16% drop and after the 400m a 25% decreased was observed. Comparing rest values with the those after the runs it was possible to verify the deteriorating force production over the event. To evaluate the strength level decrease, the subjects performed a drop jump test (from 39cm height) after the end of each of the referred distances. On different days subjects ran 400m, 100m, 200m and 300m respectively as if they where running the event (i.e. (1992) have studied the effects of fatigue on sprinters performing a 400m race.
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