The relationship between gait mechanics and walking economy throughout pregnancy

Abstract

Pregnancy is characterized by significant physiological changes that manifest through variability of symptoms, largely stemming from the weight gain, and foetal development. Consequent adaptations in posture, balance, and walking, reduce women's ability to create most comfortable and efficient movement during daily activities throughout pregnancy. As pregnancy progresses, discomfort and movement inefficiency, may significantly contribute to the total energy expenditure. However, current studies do not take in consideration the significance of gait changes and their potential in energy sparing during pregnancy. Therefore, the aim of this study was to investigate the relationship between changes in various biomechanical gait parameters, and energy expenditure during pregnancy. Thirty-five (35) women (27.5 ± 5.8 yrs) from the Tlokwe municipality volunteered for the study at different stages of pregnancy. Gas exchange via indirect calorimetry, and three-dimensional gait, and ground reaction force data were recorded while they walked at a self-selected speed. External (Wext) work was estimated assuming no energy transfer between segments, while internal work (Wint) assumed energy transfer between segments. Hence, the total energy of the body (Wtot) during gait was calculated based on the segmental changes relative to the surrounding, and relative to the centre of mass of the body. Walking speed during pregnancy was inversely associated with participants' weight (r = -0.38, p = 0.03), while weight gain during pregnancy demonstrated significant correlation with double support stance time (r = 0.37, p = 0.03). Walking speed was also significantly related to vertical excursion of the centre of gravity (r = 0.73, p ≤ 0.01), which allows for an increase in walking energy recovery with an increase in speed (r= 0.63, p ≤ 0.01). A partial correlation controlled for weeks of pregnancy showed significant, strong, positive relationship between walking speed and net O2 rate (r = 0.70, p ≤ 0.001), and no significant relationship was noted between walking speed and gross O2 rate (r = 0.32, p = 0.08) or cost (r = 0.17, p = 0.28). The weeks of gestation did not have significant influence in controlling for the relationship between walking speed and either gross or net O2 walking energy expenditure. However, 72% of variability in gross O2 was accounted for by REE which showed strong significant correlation with weight (r = 0.82, p ≤ 0.01). Stride length, adjusted for leg length, showed strong inverse correlation with the COP/COG inclination angle during walking (r = - 0.44, p ≤ 0.01), while step width, also adjusted for leg length, showed strong positive relationship with the lateral trunk lean during walking (r = 0.61, p ≤ 0.001) which was not influenced with the weeks of pregnancy, which would contribute to lateral deviations of the COG. The effect of these alterations on energy expenditure during walking may be assessed using measures of mechanical work. Both, external and internal mechanical work showed significant correlation with the indirect calorimetry. However, the strongest positive correlation was demonstrated between internal work with gross O2 cost (r = 0.81, p ≤ 0.001), and gross O2 rate (r = 0.67, p ≤ 0.001), while moderate-to-strong correlation was depicted between internal work and net O2 cost (r = 0.51, p ≤ 0.01). During pregnancy the magnitude of weight gain dictates the kinematic changes in gait and posture. While subsequent walking pattern demonstrates the need for an increase in stability, the respective changes in gait kinematics result in an increase in walking energy expenditure. Although walking economy during pregnancy may be improved via faster walking speeds, women in this study walked significantly slower, not taking the advantage of the principle of energy recovery. This demonstrates that women during pregnancy prefer a comfortable state that may be maintained the longest, rather than mechanically more economical walking. Hence, the future studies may use mechanical work and indirect calorimetry to assess changes in gait, and their contribution to walking energy expenditure.