The Effect of Unequal Crank Arm Lengths and Cycling-Specific Prostheses for Recreational Riders with a Transtibial Amputation.

PURPOSE: We determined the effects of shorter affected side crank arm lengths and cycling with two different prostheses on joint and crank power, asymmetry, and net efficiency. METHODS: 12 participants with a TTA rode at 1.5 W·kg -1 with equal (175 mm) and shorter affected side crank arms (160, 165, 170 mm) using a daily-use prosthesis and CSP. We used statistical parametric mapping to determine differences in instantaneous joint and crank power between prostheses, and linear mixed-effects models to compare average joint and crank power, asymmetry, and net efficiency. RESULTS: Shorter affected side crank arm lengths reduced the magnitude of peak positive (p ≤ 0.001) and negative (p < 0.001) crank power on the affected side. Use of a CSP increased the magnitude of peak positive knee power (p < 0.001) and decreased the magnitude of peak negative crank power (p < 0.001) on the affected side compared to a daily-use prosthesis. Shorter affected side crank arm lengths while using a CSP reduced average hip joint (p = 0.014) and hip transfer (p = 0.025) power asymmetry from 35% to 20% and 118% to 62%, respectively. However, we found no significant differences in affected side average joint or crank power, knee joint or crank power asymmetry, or net efficiency. CONCLUSIONS: Cycling at 1.5 W·kg -1 with unequal crank arm lengths and CSPs improves hip joint power and hip transfer power asymmetry but does not alter crank asymmetry or net efficiency for recreational cyclists with a TTA.

Maximum velocity and leg-specific ground reaction force production change with radius during flat curve sprinting.

Humans attain slower maximum velocity (vmax) on curves versus straight paths, potentially due to centripetal ground reaction force (GRF) production, and this depends on curve radius. Previous studies found GRF production differences between an athlete's inside versus outside leg relative to the center of the curve. Further, sprinting clockwise (CW) versus counterclockwise (CCW) slows vmax. We determined vmax, step kinematics and individual leg GRF on a straight path and on curves with 17.2 and 36.5 m radii for nine (8 male, 1 female) competitive sprinters running CW and CCW and compared vmax with three predictive models. We combined CW and CCW directions and found that vmax slowed by 10.0±2.4% and 4.1±1.6% (P<0.001) for the 17.2 and 36.5 m radius curves versus the straight path, respectively. vmax values from the predictive models were up to 3.5% faster than the experimental data. Contact length was 0.02 m shorter and stance average resultant GRF was 0.10 body weights (BW) greater for the 36.5 versus 17.2 m radius curves (P<0.001). Stance average centripetal GRF was 0.10 BW greater for the inside versus outside leg (P<0.001) on the 36.5 m radius curve. Stance average vertical GRF was 0.21 BW (P<0.001) and 0.10 BW (P=0.001) lower for the inside versus outside leg for the 17.2 and 36.5 m radius curves, respectively. For a given curve radius, vmax was 1.6% faster in the CCW compared with CW direction (P=0.003). Overall, we found that sprinters change contact length and modulate GRFs produced by their inside and outside legs as curve radius decreases, potentially limiting vmax.

The metabolic and mechanical consequences of altered propulsive force generation in walking.

Older adults walk with greater metabolic energy consumption than younger for reasons that are not well understood. We suspect that a distal-to-proximal redistribution of leg muscle demand, from muscles spanning the ankle to those spanning the hip, contributes to greater metabolic energy costs. Recently, we found that when younger adults using biofeedback target smaller than normal peak propulsive forces (FP), they do so via a similar redistribution of leg muscle demand during walking. This alludes to an experimental paradigm that emulates characteristics of elderly gait independent of other age-related changes relevant to metabolic energy cost. Thus, our purpose was to quantify the metabolic and limb- and joint-level mechanical energy costs associated with modulating propulsive forces during walking in younger adults. Walking with larger FP increased net metabolic power by 47% (main effect, p = 0.001), which was accompanied by small by relatively uniform increases in hip, knee, and ankle joint power and which correlated with total joint power (R2 = 0.151, p = 0.019). Walking with smaller FP increased net metabolic power by 58% (main effect, p < 0.001), which was accompanied by higher step frequencies and increased total joint power due to disproportionate increases in hip joint power. Increases in hip joint power when targeting smaller than normal FP accounted for more than 65% of the variance in the measured changes in net metabolic power. Our findings suggest that walking with a diminished push-off exacts a metabolic penalty because of higher step frequencies and more total limb work due to an increased demand on proximal leg muscles.