Article Title



S Sigrist


Scott Sigrist. University of Kentucky, Lexington, KY.

BACKGROUND: Sleep restriction (<7.0 h per night) afflicts more than one-third of Americans and is known to induce muscle weakness (dynapenia), but the mechanistic cause of sleep restriction-induced dynapenia (SRID) is unclear. The purpose of this study was to investigate how sleep restriction affects voluntary activation and muscle strength of the knee extensors. METHODS: Seven (2M, 5F; age 24.1±2.1y) presumably healthy, physically active subjects completed an interpolated twitch (ITT) knee extension protocol at three time points: habitual sleep (HS, 7.95±0.49h), sleep restricted (SR, 5.03±0.04h, per night for three consecutive nights), and after a seven-day washout period of habitual sleep (WO, 8.09±0.42h). Maximal strength and ITT testing were conducted the morning (9-11a local time) following the last night of sleep intervention. Subjects sat upright on an isokinetic dynamometer (Biodex S3) with the dominant leg secured at 60⁰ of knee flexion to maximize quadriceps torque. Subjects completed maximal voluntary isometric contractions (MVICs) of knee extensors. During the ITT, a constant voltage (400V) electrical stimulus (120% of current need to elicit a maximal twitch response) was delivered to the femoral nerve, before, during, and after knee extensor MVIC. We have compared MVIC and voluntary activation values by repeated measures ANOVA. Results: MVIC was not significantly different between SA and SR (192.3±39.2 vs. 181.5±35.3 Nm, p=0.370). However, MVIC was greater in WO (204.3±41.86 Nm) compared to SR (p=0.008), but not SA (p=0.390). Voluntary activation of the quadriceps was not significantly different among the three time points (SA: 89.9±6.6, SR: 93.6±2.7, and WO: 87.4±12.5%, p=0.359). Conclusions: Three nights of sleep restriction did not significantly alter knee extension MVIC, however, seven nights of sleep extension significantly increased MVIC following a short bout of SR which was not explained by changes in voluntary activation.

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