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External resistance is imperative for training-induced efferent neural drive enhancement in older adults
Unhjem R, Toien T, Kvellestad ACG, Oren TS, Wang E
The Journals of Gerontology. Series A, Biological Sciences and Medical Sciences 2021 Feb;76(2):224-232
clinical trial
5/10 [Eligibility criteria: Yes; Random allocation: Yes; Concealed allocation: No; Baseline comparability: Yes; Blind subjects: No; Blind therapists: No; Blind assessors: No; Adequate follow-up: Yes; Intention-to-treat analysis: No; Between-group comparisons: Yes; Point estimates and variability: Yes. Note: Eligibility criteria item does not contribute to total score] *This score has been confirmed*

Strength training performed with heavy loads and maximal intended velocity is documented to enhance efferent neural drive to maximally contracting musculature in older adults. However, it remains unclear whether the neural plasticity following training result from motor skill learning or if external resistance is a prerequisite. To investigate this, we assessed electrically evoked potentials (h-reflex and v-waves normalized to maximal m-wave) and voluntary activation (VA) in 36 older adults (73 +/- 4 years) randomized to 3 weeks of plantar flexion strength training, with (maximal strength training; MST) or without (unloaded ballistic training; UBT) heavy external loading (90% of one repetition maximum), or a control group. Both training groups aimed to execute the concentric phase of movement as fast and forcefully as possible. The MST group improved maximal voluntary contraction (MVC) and rate of force development (RFD) by 18 +/- 13% (p = 0.001; Hedges g = 0.66) and 35 +/- 17% (p < 0.001; g = 0.94), respectively, and this was different (MVC p = 0.013; RFD p = 0.001) from the UBT group which exhibited a 7 +/- 8% (p = 0.033; g = 0.32) increase in MVC and a tendency to increase RFD (p = 0.119; g = 0.22). Concomitant improvements in efferent neural drive (Vmax/Msup-ratio 0.14 +/- 0.08 to 0.24 +/- 0.20; p = 0.010) and a tendency towards increased VA (79 +/- 9% to 84 +/- 5%; p = 0.098), were only apparent after MST. No changes were observed in Hmax/Mmax-ratio for the groups. In conclusion, external loading during exercise training appears to be a prerequisite for efferent neural drive enhancement in older adults. Thus, strength training with heavy loads should be recommended to counteract the typically observed age-related decline in motoneuron firing frequency and recruitment.
Copyright the Gerontological Society of America. Reproduced by permission of the publisher.

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