Faculty of Health and Life Sciences, Northumbria University , Newcastle Upon Tyne , United Kingdom.
Université Lyon, UJM-Saint-Etienne, Inter-university Laboratory of Human Movement Biology, Saint-Etienne, France.
J Appl Physiol (1985). 2019 Apr 1;126(4):1015-1031. doi: 10.1152/japplphysiol.00987.2018. Epub 2019 Feb 7.
The aim of this study was to assess differences in motor performance, as well as corticospinal and spinal responses to transcranial magnetic and percutaneous nerve stimulation, respectively, during submaximal isometric, shortening, and lengthening contractions between younger and older adults. Fifteen younger [26 yr (SD 4); 7 women, 8 men] and 14 older [64 yr (SD 3); 5 women, 9 men] adults performed isometric and shortening and lengthening dorsiflexion on an isokinetic dynamometer (5°/s) at 25% and 50% of contraction type-specific maximums. Motor evoked potentials (MEPs) and H reflexes were recorded at anatomical zero. Maximal dorsiflexor torque was greater during lengthening compared with shortening and isometric contractions ( P < 0.001) but was not age dependent ( P = 0.158). However, torque variability was greater in older compared with young adults ( P < 0.001). Background electromyographic (EMG) activity was greater in older compared with younger adults ( P < 0.005) and was contraction type dependent ( P < 0.001). As evoked responses are influenced by both the maximal level of excitation and background EMG activity, the responses were additionally normalized {[MEP/maximum M wave (M)]/root-mean-square EMG activity (RMS) and [H reflex (H)/M]/RMS}. (MEP/M)/RMS and (H/M)/RMS were similar across contraction types but were greater in young compared with older adults ( P < 0.001). Peripheral motor conduction times were prolonged in older adults ( P = 0.003), whereas peripheral sensory conduction times and central motor conduction times were not age dependent ( P ≥ 0.356). These data suggest that age-related changes throughout the central nervous system serve to accommodate contraction type-specific motor control. Moreover, a reduction in corticospinal responses and increased torque variability seem to occur without a significant reduction in maximal torque-producing capacity during older age. NEW & NOTEWORTHY This is the first study to have explored corticospinal and spinal responses with aging during submaximal contractions of different types (isometric, shortening, and lengthening) in lower limb musculature. It is demonstrated that despite preserved maximal torque production capacity corticospinal responses are reduced in older compared with younger adults across contraction types along with increased torque variability during dynamic contractions. This suggests that the age-related corticospinal changes serve to accommodate contraction type-specific motor control.
本研究旨在评估年轻和老年成年人在进行亚最大等长、缩短和延长收缩时，运动表现以及经颅磁和经皮神经刺激的皮质脊髓和脊髓反应的差异。15 名年轻成年人[26 岁（SD 4）；7 名女性，8 名男性]和 14 名老年成年人[64 岁（SD 3）；5 名女性，9 名男性]在等速测力计上进行 5°/s 的等长和缩短以及背屈延长收缩，收缩幅度为各收缩类型最大收缩幅度的 25%和 50%。在解剖学零位记录运动诱发电位（MEPs）和 H 反射。与缩短和等长收缩相比，延长收缩时最大背屈扭矩更大（P < 0.001），但与年龄无关（P = 0.158）。然而，与年轻成年人相比，老年成年人的扭矩变异性更大（P < 0.001）。与年轻成年人相比，老年成年人的背景肌电图（EMG）活动更大（P < 0.005），并且与收缩类型有关（P < 0.001）。由于诱发反应受到最大兴奋水平和背景 EMG 活动的影响，因此还对反应进行了归一化处理[MEP/最大 M 波（M）]/均方根 EMG 活动（RMS）和[H 反射（H）/M]/RMS]。（MEP/M）/RMS 和（H/M）/RMS 在各收缩类型之间相似，但在年轻成年人中大于老年成年人（P < 0.001）。与年轻成年人相比，老年成年人的外周运动传导时间延长（P = 0.003），而外周感觉传导时间和中枢运动传导时间与年龄无关（P ≥ 0.356）。这些数据表明，与年龄相关的中枢神经系统变化有助于适应下肢肌肉不同收缩类型的特定运动控制。此外，在老年时期，皮质脊髓反应减少和扭矩变异性增加似乎并未导致最大扭矩产生能力显著降低。本研究首次探索了亚最大等长、缩短和延长收缩等不同收缩类型下，下肢肌肉的皮质脊髓和脊髓反应随年龄的变化。结果表明，尽管最大扭矩产生能力保持不变，但与年轻成年人相比，老年成年人在各收缩类型下的皮质脊髓反应均降低，且在动态收缩时扭矩变异性增加。这表明与年龄相关的皮质脊髓变化有助于适应收缩类型特定的运动控制。
