Table 2.
Regression Models Testing Associations of k PCr and VO2 With Gait Speed in the Four Gait Tasks
| Age (per 10 y) | k PCr (s−1) | PCr depletion (*10%) | Peak VO2 (mL/kg/min) | Model R 2 | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Outcome | Model | Beta (95% CI) | p Value | Beta (95% CI) | p Value | Beta (95% CI) | p Value | Beta (95% CI) | p Value | |
| Usual gait speed (6 m), m/s | Model 1 | −0.069 (−0.098, −0.039) | <.001 | .194 | ||||||
| Model 2 | −0.064 (−0.096, −0.032) | <.001 | 2.495 (−3.257, 8.247) | .392 | 0.035 (−0.004, 0.073) | .077 | .216 | |||
| Model 3 | −0.040 (−0.080, −0.001) | .047 | 0.009 (0.001, 0.018) | .042 | .222 | |||||
| Model 4 | −0.042 (−0.082, −0.002) | .038 | 0.301 (−5.915, 6.517) | .924 | −0.027 (−0.012, 0066) | .171 | 0.008 (−0.001, 0.019) | .082 | .236 | |
| Usual gait speed (150s), m/s | Model 1 | −0.047 (−0.068, −0.026) | <.001 | .169 | ||||||
| Model 2 | −0.035 (−0.058, −0.013) | .003 | 5.238 (1.163, 9.314) | .012 | −0.018 (−0.009, 0.045) | .188 | .213 | |||
| Model 3 | −0.006 (−0.033, 0.021) | .664 | 0.013 (0.007, 0.019) | <.001 | .286 | |||||
| Model 4 | −0.005 (−0.033, 0.022) | .696 | 2.158 (−2.197, 5.536) | .315 | −0.008 (−0.019, 0.034) | .57 | 0.012 (0.005, 0.018) | <.001 | .292 | |
| Rapid gait speed (6 m), m/s | Model 1 | −0.134 (−0.178, −0.090) | <.001 | .271 | ||||||
| Model 2 | −0.102 (−0.148, −0.056) | <.001 | 14.299 (6.007, 22.252) | .001 | −0.043 (−0.012, 0.099) | .124 | .337 | |||
| Model 3 | −0.071 (−0.129, −0.013) | .017 | 0.020 (0.007, 0.033) | .002 | .326 | |||||
| Model 4 | −0.068 (−0.125, −0.010) | .021 | 10.798 (0.605, 19.733) | .018 | −0.031 (−0.025, 0.088) | .271 | 0.013 (−0.001, 0.027) | .054 | .358 | |
| Rapid gait speed (400 m), m/s | Model 1 | −0.134 (−0.163, −0.104) | <.001 | .431 | ||||||
| Model 2 | −0.112 (−0.143, −0.081) | <.001 | 9.839 (4.321, 15.356) | .001 | −0.036 (−0.001, 0.073) | .056 | .487 | |||
| Model 3 | −0.071 (−0.108, −0.034) | <.001 | 0.020 (0.012, 0.028) | <.001 | .528 | |||||
| Model 4 | −0.070 (−0.106, −0.033) | <.001 | 5.478 (−0.222, 11.178) | .059 | −0.021 (−0.015, 0.057) | .249 | 0.017 (0.008, 0.026) | <.001 | .543 | |
Notes: CI = confidence interval; k PCr = phosphocreatine recovery rate; VO2 = oxygen consumption.
All models additionally adjusted for sex, height, and weight. Model 1 estimated the coefficient linking age to walking speed; Model 2 also incorporated age, k PCr, and %PCr depletion. This model tested whether mitochondrial function is a significant independent correlate of walking speed and, when compared with Model 1, whether changes with age in mitochondrial function account for the decline of walking speed with aging; Model 3 added peak VO2 to Model 1 and tests whether aerobic fitness is an independent correlate of walking speed and, when compared with Model 1, whether changes with age in aerobic fitness account for the decline of walking speed with aging; Model 4 included age, k PCr, %PCr depletion, and peak VO2 to test whether mitochondrial function estimated by magnetic resonance spectroscopy and fitness estimated by treadmill testing, are independent correlates of walking speed.