Influence of excess weight on lower-extremity vertical stiffness and metabolic cost of walking

ABSTRACT

The purpose was to test whether lower-extremity vertical stiffness and gait mechanics explain differences in energy cost of walking (Cw) between individuals with normal weight (NW) and obesity (OB). Ten OB (33.1 ± 2.0 kg m⁻²) and 10 NW (24.2 ± 1.3 kg m⁻²) walked for six minutes on an instrumented treadmill at 1.25 m s⁻¹ while Cw, lower-extremity kinematics, and vertical stiffness (K_vert) were measured. NW completed another trial with a loaded vest (NWL) to simulate the BMI of the obese group. Cw was 24% greater in OB (277.5 ± 45.3 J m⁻¹) and 23% greater in NWL (272.7 ± 35.7 J m⁻¹) than NW (211.0 ± 27.0 J m⁻¹, P < 0.005). Mass-specific Cw (Cw_kg) wasn’t different between conditions (P = 0.085). Lower-extremity K_vert was 40% higher in OB (32.7 ± 5.2 kN m⁻¹) than NW (23.3 ± 4.7 kN m⁻¹, P < 0.001), but neither was different from NWL (27.5 ± 3.4 kN m⁻¹, P > 0.05). Mass-specific K_vert (P = 0.081) was similar across conditions. K_vert was related to Cw (r = 0.55, P = 0.001). Cw_kg wasn’t different between NW or OB, but there was a negative correlation between BMI and Cw_kg driven by lower Cw_kg in NWL. Cw and K_vert covaried in proportion to body mass, but mass-specific K_vert was unrelated to Cw_kg. Mass-specific K_vert was lower in NWL than OB due to NWL’s greater angle of attack, center of mass displacement, and joint range of motion.

Keywords:

• Obesity
• load carriage
• leg kinematics
• walking economy
• metabolic cost

Acknowledgements

The authors would like to thank Sarah Bergstrom for her help during data collection and Morgan Baumgartner and Victoria Libby for their assistance with data analysis.

Disclosure statement

No potential conflict of interest was reported by the authors.