Neuromuscular determinants of maximum walking speed in well-functioning older adults

Authors: CLARK, DAVID - University Of Florida; MANINI, TODD - University Of Florida; FIELDING, ROGER - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; PATTEN, CAROLYNN - University Of Florida

Submitted to: Experimental Gerontology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/22/2013
Publication Date: 3/1/2013
Citation: Clark, D., Manini, T.M., Fielding, R.A., Patten, C. 2013. Neuromuscular determinants of maximum walking speed in well-functioning older adults. Experimental Gerontology. 48(3):358-363.

Interpretive Summary: 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 force. To test this we had participants walk at their usual walking speed. Based on how fast or slow they walked, we put them into two groups; the ‘Slower’ Group and the ‘Faster’ Group. Then we assessed their muscle movements. Muscle sections were examined using Magnetic Resonance Imaging (MRI). Our findings support the conclusion that maximum walking speed is limited by impaired neuromuscular force and activation of the calf muscle group. Future research should further evaluate the utility of maximum walking speed for use in clinical assessment to detect and monitoring age-related functional decline.

Technical Abstract: 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 walking speed >1.0 m/s. If the difference between usual and maximum 10m walking speed was < 0.6 m/s, the individual was assigned to the "Slower" group (n=8). If the difference between usual and maximum 10-meter walking speed was > 0.6 m/s, the individual was assigned to the "Faster" group (n=12). Peak rate of triceps surae force production and neuromuscular activation (rate of EMG rise) 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. 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 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 monitoring age-related functional decline.