Brain Rehabilitation Research Center, Malcom Randall VA Medical Center, Gainesville, FL 32608-1135, USA.
Exp Gerontol. 2013 Mar;48(3):358-63. doi: 10.1016/j.exger.2013.01.010. Epub 2013 Jan 29.
Maximum walking speed may offer an advantage over usual walking speed for clinical assessment of age-related declines in mobility function that are due to neuromuscular impairment. The objective of this study was to determine the extent to which maximum walking speed is affected by neuromuscular function of the lower extremities in older adults. We recruited two groups of healthy, well functioning older adults who differed primarily on maximum walking speed. We hypothesized that individuals with slower maximum walking speed would exhibit reduced lower extremity muscle size and impaired plantarflexion force production and neuromuscular activation during a rapid contraction of the triceps surae muscle group (soleus (SO) and gastrocnemius (MG)). All participants were required to have usual 10-meter walking speed of >1.0m/s. If the difference between usual and maximum 10m walking speed was <0.6m/s, the individual was assigned to the "Slower" group (n=8). If the difference between usual and maximum 10-meter walking speed was >0.6m/s, the individual was assigned to the "Faster" group (n=12). Peak rate of force development (RFD) and rate of neuromuscular activation (rate of EMG rise) of the triceps surae muscle group were assessed during a rapid plantarflexion movement. Muscle cross sectional area of the right triceps surae, quadriceps and hamstrings muscle groups was determined by magnetic resonance imaging. Across participants, the difference between usual and maximal walking speed was predominantly dictated by maximum walking speed (r=.85). We therefore report maximum walking speed (1.76 and 2.17m/s in Slower and Faster, p<.001) rather than the difference between usual and maximal. Plantarflexion RFD was 38% lower (p=.002) in Slower compared to Faster. MG rate of EMG rise was 34% lower (p=.01) in Slower than Faster, but SO rate of EMG rise did not differ between groups (p=.73). Contrary to our hypothesis, muscle CSA was not lower in Slower than Faster for the muscle groups tested, which included triceps surae (p=.44), quadriceps (p=.76) and hamstrings (p=.98). MG rate of EMG rise was positively associated with RFD and maximum 10m walking speed, but not the usual 10m walking speed. These findings support the conclusion that maximum walking speed is limited by impaired neuromuscular force and activation of the triceps surae muscle group. Future research should further evaluate the utility of maximum walking speed for use in clinical assessment to detect and monitor age-related functional decline.
最大步行速度可能比通常的步行速度更有利于评估因神经肌肉损伤导致的与年龄相关的移动功能下降。本研究的目的是确定最大步行速度在多大程度上受到老年人下肢神经肌肉功能的影响。我们招募了两组健康、功能良好的老年人，他们主要的区别在于最大步行速度。我们假设，最大步行速度较慢的个体在快速收缩比目鱼肌和腓肠肌（SO 和 MG）时，下肢肌肉大小会减小，并且跖屈力产生和神经肌肉激活会受到损害。所有参与者的通常 10 米步行速度都必须大于 1.0m/s。如果通常的 10 米行走速度和最大行走速度之间的差异小于 0.6m/s，则将个体分配到“较慢”组（n=8）。如果通常的 10 米行走速度和最大行走速度之间的差异大于 0.6m/s，则将个体分配到“较快”组（n=12）。在快速跖屈运动过程中，评估比目鱼肌的最大力量发展速率（RFD）和神经肌肉激活速率（EMG 上升速率）。通过磁共振成像确定右侧比目鱼肌、股四头肌和腘绳肌的肌肉横截面积。在所有参与者中，通常和最大步行速度之间的差异主要由最大步行速度决定（r=.85）。因此，我们报告最大步行速度（较慢者为 1.76 和 2.17m/s，较快者为 1.76 和 2.17m/s，p<.001），而不是通常和最大速度之间的差异。与较快者相比，较慢者的跖屈 RFD 降低了 38%（p=.002）。较慢者的 MG EMG 上升速率比较快者低 34%（p=.01），但 SO EMG 上升速率在两组之间没有差异（p=.73）。与我们的假设相反，在测试的肌肉群中，较慢者的肌肉横截面积并不低于较快者，包括比目鱼肌（p=.44）、股四头肌（p=.76）和腘绳肌（p=.98）。MG 的 EMG 上升速率与 RFD 和最大 10 米步行速度呈正相关，但与通常的 10 米步行速度无关。这些发现支持这样的结论，即最大步行速度受到比目鱼肌神经肌肉力量和激活的限制。未来的研究应进一步评估最大步行速度在临床评估中的效用，以检测和监测与年龄相关的功能下降。
