| Popis: |
Examine the effects of 42°C hot-water immersion on muscle contraction function and motor unit discharge rates.Fifteen participants (24.9±5.6 years) performed neuromuscular assessments before, after, and ~15-min after either 90-min of 42°C or 36°C water immersion. Maximal voluntary contraction (MVC) assessment of knee extension was performed along with surface electromyography (sEMG) (vastus lateralis and medialis [VL, VM]) and voluntary activation level (VAL). Resting evoked twitch was elicited for peak torque and time to peak torque analysis. In addition, the VL and VM motor unit mean discharge rates (MUDR) were measured.After hot-water immersion (core temperature ↑1°C; muscle temperature ↑2.4°C), MVC torque and VAL decreased (p.05). The sEMG (VL and VM) and peak twitch torque did not change (p.05), while time to peak torque decreased (p=.007). The VL and VM MUDR decreased, showing a time effect, after both water immersion conditions (36°C and 42°C) (p.001). Fifteen minutes after the hot-water immersion (core temperature at baseline; muscle temperature ↑1.4°C), MVC torque returned to baseline, but VAL remained lower. The sEMG (VL and VM) remained unchanged. Peak twitch torque increased (p.002) and time to peak torque remained lower (p=.028). The MUDR remained lower after both water immersion conditions (p.05).Increased core temperature evoked by 42°C hot-water immersion decreases MVC torque and VAL. However, a passive increase in muscle temperature improved muscle evoked contractile function (i.e., peak twitch torque and time to peak torque). Moreover, a passive increase in muscle temperature reduced the required MUDR to attain the same torque. |
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