After revision of the literature (Celichowski et al, 2006; Hubal et al., 2006), we hypothesized that contraction (CT) and relaxation time (RT) should increase because of fatigue. Nevertheless the use of different contraction modes such as voluntary contraction, evoked force or single twitches may certainly affect the results. Material and Methods: 20 subjects carried out an intermittent protocol composed by 25 rounds as maximum. Each round was composed by two sections: 1) composed by six 5 s-voluntary contractions of 30% MVC, with resting periods of 5 s, 2) To mainly assess the effect of fatigue, composed of 3 s MVC followed by 1-min-resting period and a 50% MVC maintained during 10 s. The force exerted against the brake lever, time to MVC (CT) and half time to relaxation (1/2RT) were measured by a unidirectional gauge connected to a MuscleLab system. A ME6000 EMG system was used to register flexor digitorum superficialis (FS) and carpi radialis (CR) EMG signal signal during MVCs was RMS. The number of rounds of each subjects was normalized (Mamaghani et al., 2002). Each relative round (n=4) corresponds to the 25% of the test for each subject. Repeated measures ANOVAs and regression analysis were used to study changes in the NMVC, RMS, Ct and 1/2RT. Results: Significant decrement of the NMVC and RMS MVC of the Carpi radialis (CR) and flexor superficialis (FS) were observed (p.0.001). No significant differences were found for the CT (F(4,16)=2.69; p=0.069). Nevertheless, for the 1/2RT significant differences were observed (F(4,16)=13,51; p.0.001). Post-hoc analysis revealed differences only between the basal 1/2RT value and the four relative rounds (p.0.001) whereas no significant trend was observed throughout the fatigue protocol (F(3,17)=1.88; p=0.171). Regression analysis showed a significant decrement (p .0.05) in 35% of the subjects with CT and 15% with 1/2RT. Discussion: The decrement of NMVC and RMS MVC confirm the occurrence of fatigue. From the very beginning of the fatigue protocol 1/2RT is longer in comparison to the non fatigued state of the basal assessment. This result confirm only partially previous authors (Celichowski et al, 2006; Hubal et al., 2006; Orizio et al., 1999) possibly because they used electrically evoked single twitches instead of MVC as in our study.
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