Sprinter’s motor signature does not change with fatigue

Abstract

The aim of this study was to investigate human adaptations to fatigue induced by track sprint repetitions. Eight male sprinters were asked to run 4 × 100 m as quickly as possible with 3 min of recovery. Subjects were filmed (50 Hz) in order to measure stride length and frequency. Velocity was measured by means of radar (250 Hz) while contact and flight times were registered wirelessly by two pressure sensors (400 Hz) embedded under the insole of the subjects' shoes. Contact and flight times were used to calculate stiffness. In addition, blood samples were taken prior to warm-up, 1 min after each 100-m sprint and every 2 min after the last repetition until a lactate peak ([BLa]) was reached. [BLa] did not affect mechanical and stride parameters. Inter-series ANOVA showed that velocity decreased significantly (-3.55%) between Repetition 1 (8.18 ± 0.29 m s(-1)) and Repetition 4 (7.89 ± 0.42 m s(-1)), while [BLa] increased from 6.74 ± 1.15 to 13.58 ± 1.48 mmol l(-1) (p < 0.05). The first main result was that leg stiffness remained constant until Repetition 3 and then dramatically increased at Repetition 4, whereas vertical stiffness remained constant throughout all four repetitions. This behavior could be considered to be a neuromuscular adaptation to fatigue used by skilled athletes. The second main result was that velocity decreased during the second phase (30-80 m) of the entire 100 m. In addition, a PCA revealed three different sprint profiles explaining 88.2% of the total variance: the contact-time-pattern (39.46%), force-pattern (27.96%) and stride-pattern (20.77%). Two different motor signatures were identified with fatigue. In the first, athletes switch from the key variable to another when exhausted without changing their motor behavior (during Repetition 3 and/or Repetition 4). In the second, athletes do not change their motor behavior with fatigue.

Physiological, neuromuscular and perceived exertion responses in badminton games

“…LS remained unchanged with fatigue until the end of the match, despite a slight insignificant decrease (-10%). Such an insignificant decrease with fatigue has been noticed previously during sprint repetition (Choukou, Laffaye, & Heugas-De Panafieu, 2012) and prolonged tennis matches (Girard et al, 2006). The correlation observed between the decline in SJ and CMJ power with LS (r = 0.782 and r = 0.613, respectively) reveals that the ability to maintain a high level of force and power output is regulated by LS.…”

“…previously considered as neuromuscular adaptation to fatigue (Choukou et al, 2012). The insignificant decrease in LS in correlation with a significant decreased in lower-limb power suggests that the central nervous systems modified the control pattern to maintain constant stiffness as previously shown in various motor tasks such as repeated sprint (Choukou et al, 2012) and to regulate movement reorganization under fatigue. Leg properties can be modified by stiffness regulation during SSC tasks, whereas the high number of motor units required jumping high during a SJ or a CMJ declines with fatigue.…”