Correlating mechanical work with energy consumption during gait throughout pregnancy

Abstract

BackgroundMeasures of mechanical work may be useful in evaluating efficiency of walking during pregnancy. Various adaptations in the body during pregnancy lead to altered gait, consequently contributing to the total energy cost of walking. Measures of metabolic energy expenditure may not be reliable for measuring energetic cost of gait during pregnancy as pregnancy results in numerous metabolic changes resulting from foetal development. Therefore, the aim of this study is to determine if mechanical work prediction equations correlate with the metabolic energy cost of gait during pregnancy.MethodsThirty-five (35) women (27.5 ± 6.1 years) gave informed consent for participation in the study at different weeks of gestation pregnancy. Gas exchange and gait data were recorded while walking at a fixed self-selected walking speed. External (Wext) work was estimated assuming no energy transfer between segments, while internal work (Wint) assumed energy transfer between segments. Hence total energy of the body (Wtot) was calculated based on the segmental changes relative to the surrounding, and relative to the centre of mass of the whole body. Equations for mechanical work were correlated with net and gross O2 rate, and O2 cost.ResultsExternal, internal and total mechanical energy showed significant positive relationship with gross O2 rate (r = 0.48, r = 0.35; and r = 0.49 respectively), and gross O2 cost (r = 0.42; r = 0.70, and r = 0.62, respectively). In contrast, external, internal and total mechanical energy had no significant relationship with net O2 rate (r = 0.19, r = 0.24, and r = 0.24, respectively). Net O2 cost was significant related Wext (r = 0.49) Wint (r = 0.66) and Wtot (r = 0.62). Energy recovery improved with increase in gait speed.ConclusionsMeasures of mechanical work, when adjusted for resting energy expenditure, and walking speed may be useful in comparing metabolic energy consumption between women during pregnancy, or assessment or gait changes of the same individual throughout pregnancy.

Relationship between gait kinematics and walking energy expenditure during pregnancy in South African women

“…Given that the motion of the COG may be regarded as the summation of all forces that act on the body, the significant portion of the total metabolic cost during walking should be attributed to the work required to move the COG [ 5 , 6 ], especially as the weight of the body increases as in pregnancy. This effect has been demonstrated in our previous article [ 4 ]. This relationship indicates that the ability to increase walking efficiency is related to the principle of conservation of mechanical energy during walking that is maximized at certain speeds [ 4 , 5 , 25 ], which participants in this study did not reach.…”

“…Procedures for walking and resting energy expenditure, and gait analysis were previously described in Krkeljas and Moss [ 4 ], hence only a brief description of the methodology will be provided in the following section.…”

“…However, the energy required for foetal development is relatively small [ 3 ], and well-nourished mothers have adequate fat stores to provide for the additional energy needed for development. Although reducing the amount of walking or even reducing the walking speed are behavioural changes in daily activities that may result in reduction of total daily energy expenditure (TEE) [ 2 ], other changes in gait mechanics during pregnancy may lead to an increase in walking energy expenditure [ 4 ]. Yet, it is not clear if the relative energy changes as a result of alterations in gait mechanics have a significant impact on overall energy balance during pregnancy.…”

“…The change in trunk moment of inertia during pregnancy causes various compensations and adaptions in posture and gait mechanics that may result in the increase in walking energy expenditure [ 4 ]. As a significant portion of the metabolic cost of walking is attributed to the work required to move the body’s centre of mass (COM) [ 5 , 6 ], any changes in gait kinematics affecting path of the COM would reflect on the energy expenditure [ 4 ].…”

“…The change in trunk moment of inertia during pregnancy causes various compensations and adaptions in posture and gait mechanics that may result in the increase in walking energy expenditure [ 4 ]. As a significant portion of the metabolic cost of walking is attributed to the work required to move the body’s centre of mass (COM) [ 5 , 6 ], any changes in gait kinematics affecting path of the COM would reflect on the energy expenditure [ 4 ]. It is well established that changes in gait kinematics are associated with changes in primary gait determinants [ 7 , 8 ] which may lead to increase in metabolic cost of locomotion, yet there is a lack of studies investigating this relationship during pregnancy.…”