Abstract
This study aimed to clarify the activation characteristics of the vastus lateralis muscle in the front leg during timing correction for a sudden decrease in the velocity of a target during baseball swings. Eleven male collegiate baseball players performed coincident timing tasks that comprised constant velocity of 8 m/s (unchanged) and a sudden decrease in velocity from 8 to 4 m/s (decreased velocity). Electromyography (EMG) revealed that the muscle activation was typically monophasic when responding unchanged conditions. The type of muscle activation during swings in response to decreased velocity condition was both monophasic and biphasic. When biphasic activation appeared in response to decreased velocity, the impact time and the time to peak EMG amplitude were significantly prolonged and the timing error was significantly smaller than that of monophasic activation. However, the EMG onset from the target start was consistent both monophasic and biphasic activation in response to conditions of decreased velocity. In addition, batters with small timing errors in response to decreased velocity were more likely to generate biphasic EMG activation. These findings indicated that timing correction for a sudden decrease in the velocity of an oncoming target is achieved by modifying the muscle activation characteristics of the vastus lateralis muscle of front leg from monophasic to biphasic to delay reaching peak muscle activation and thus prolong impact time. Therefore, the present findings suggests that the extent of timing errors in response to decreased velocity is influenced by the ability to correct muscle activation after its initiation rather than by delaying the initiation timing of muscle activation during baseball swings.
Highlights
The timely interception of a high-velocity object such as a ball using batting tools is one of the most difficult perceptual motor acts that a human can perform [1]
We hypothesized that due to unexpected changes in target status, swing timing is corrected by modifying knee extensor muscle activation strategy in the front leg
Monophasic and biphasic EMG activation was evident in response to decreased target velocity condition (DV) (Fig 1)
Summary
The timely interception of a high-velocity object such as a ball using batting tools is one of the most difficult perceptual motor acts that a human can perform [1]. When a batter can precisely predict the moment at which a thrown ball arrives, it can be hit by swinging the bat to the impact position at the appropriate time. Skilled cricket players can alter the swing of their bats within ~ 190 ms of the moment when a ball bounces oddly [5] This finding indicates that batters can rapidly adjust and correct the swing and its timing to unexpected perturbations of ball trajectories. Correcting swing timing due to unexpected changes in the status of a target such as in velocity and/or impact point is associated with adjusting the activities of upper limb muscles [6]. We hypothesized that due to unexpected changes in target status, swing timing is corrected by modifying knee extensor muscle activation strategy in the front leg
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