Abstract
While the incidence of falls has been described to increase with pregnancy, the mechanism behind this is unclear. Pregnancy associated changes in lower extremity muscle strength could be a possible factor influencing injury risk. Thus, the aim of this longitudinal study was to investigate muscle strength and architectural properties of the lower limbs in different stages of pregnancy and postpartum. In nineteen pregnant women (30 ± 4 years) and fifteen non-pregnant controls (28 ± 4 years) muscle strength and architectural properties of the vastus lateralis muscle were assessed combining dynamometry, ultrasound, kinematic, and electromyographic measurements. Body mass and body composition were determined using bioimpedance analysis. In the pregnant women, the measurements were conducted in the 16 ± 4th (EP) and 29 ± 4th week of pregnancy (LP) as well as in the 32 ± 9th week postpartum (PP). Muscle thickness and pennation angle of the fascicles significantly increased at LP, while muscle strength remained constant during and after pregnancy. Body mass, skeletal muscle mass, fat mass, intracellular and extracellular water also peaked at LP. Postpartum values did not differ from the controls. Changes in the muscle properties were not related to changes in body mass and body composition. Conditions during pregnancy promote changes in the vastus lateralis architecture indicating muscle hypertrophy. However, pregnancy did not increase muscle strength while body mass progressively increases. Therefore, in the event of balance perturbations pregnant women may not be able to meet the requirements for the increased physical demand.
Highlights
Positive effects of exercise during pregnancy are well documented
While knee extensor muscle strength remained constant during and after pregnancy we found an increase in muscle thickness and pennation angle of the vastus lateralis in the late stage of pregnancy returning to non-pregnant levels in the postpartum phase
It is conceivable that the increase in muscle thickness may have been influenced at least partly by changes in water content during pregnancy, since we detected a significant increase of the intracellular and extracellular water at the late stage of pregnancy
Summary
Positive effects of exercise during pregnancy are well documented. regular exercise during pregnancy is recommended to reduce pregnancy associated symptoms such as hypertension or gestational diabetes, as well as to maintain muscle strength and endurance to prepare for delivery (Vladutiu et al, 2010; Nascimento et al, 2012). Pregnant women have repeatedly been observed to suffer from reduced static and dynamic postural stability compared to non-pregnant women (Oliveira et al, 2009; Inanir et al, 2014; Bey et al, 2018). These impairments in stability are assumed to contribute to the increased number of falls (Inanir et al, 2014)
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