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- W2000950270 abstract "Vibrating a muscle tendon generates sufficient Ia afferent input to the spinal cord to recruit individual single motor units (MU) and cause a reflex contraction. When the force profile is reproduced voluntarily, the same MU is recruited at a higher recruitment threshold (RT) and at a higher firing rate (FR) compared to reflex activation. This suggests that MU may be activated via two different pathways. To determine if this change is due to alterations in descending drive we increased central excitability by administering caffeine, which is known to act centrally and is excitatory to the MU pool during voluntary activation. PURPOSE The purpose of the present experiment was to compare the effects of caffeine on the RT and FR of MU in the vastus lateralis (VL) during reflex and voluntary contractions. We hypothesized that there would be a decrease in the RT and an increase in the average FR in the caffeine condition during voluntary activation and that caffeine would have no effect during reflex activation. METHODS MU recordings were obtained using tungsten microelectrodes from the VL on 2 separate days (caffeine and placebo). Vibration (175 Hz) was applied to the patellar tendon for 30 to 35s. After a 90s rest period, and without moving the electrode, the force profile was reproduced voluntarily. This allowed us to observe the behaviour of the same MU activated under both conditions. RESULTS The results showed that during reflex activation the RT and FR were significantly lower for all conditions. There was a significant increase in the FR of MU during voluntary activation in the caffeine condition but no changes were observed in FR during reflex activation. There were no alterations in the RT in either condition. CONCLUSION We demonstrated that caffeine only exerts its effects during voluntary activation of muscle, and does not alter peripheral feedback from muscle spindles. Caffeine's potentiating effects on MU FR may be due to an increase in the central excitatory neurotransmitters serotonin and norepinephrine, which are known to increase with caffeine ingestion. Supported by NSERC" @default.
- W2000950270 created "2016-06-24" @default.
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- W2000950270 date "2003-05-01" @default.
- W2000950270 modified "2023-09-25" @default.
- W2000950270 title "CAFFEINE ALTERS VOLUNTARY BUT NOT REFLEX ACTIVATION OF SINGLE HUMAN MOTOR UNITS" @default.
- W2000950270 doi "https://doi.org/10.1097/00005768-200305001-01559" @default.
- W2000950270 hasPublicationYear "2003" @default.
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