Hip torques and the effect of posture in side-stepping with elastic resistance.

BACKGROUND: The way movement-based exercises affect targeted muscles is not always obvious. Side stepping with an elastic band around the forefeet is aimed at strengthening hip abductors and lateral rotator muscles, with the premise that it creates an external torque of adduction and medial rotation of the femur around the pelvis that needs to be counteracted by hip muscles. However, hip torques during this exercise have not been previously quantified. RESEARCH QUESTION: Is the premise that the side-stepping exercise creates an external torque of adduction and medial rotation of the femur around the pelvis correct? METHODS: Thirty-six adults performed the exercise in an upright and a squat posture while 3D kinetic and kinematic data were collected. Hip muscle torques were calculated using inverse dynamics. The effect of posture and potential interactions with sex, side-stepping phases, and trailing/leading directions were analyzed using Pearson correlation and mixed-model ANOVAs. RESULT: A hip net muscle torque of extension, abduction and medial rotation was required to perform the exercise, regardless of phase and direction. The net muscle torque towards medial rotation required during the exercise was smaller (P < 0.001) in the upright (0.05-0.12 N m kg-1 m-1 across phases) compared to the squat posture (0.10-0.24 N m kg-1 m-1). In contrast, hip abductor torque was not affected by posture. When averaged across phases and directions, the normalized hip medial rotator muscle torque was highly correlated with knee flexion (r = 0.93, P < 0.001). SIGNIFICANCE: The assumption that the side-stepping with the elastic band on the forefeet creates an external hip torque of medial rotation is erroneous. The resistance imposed to the hip during this exercise is consistent with the goal of strengthening the muscles that contribute to hip abduction and hip medial (not lateral) rotation. Changing the knee flexion angle is an effective way to manipulate hip rotator torque when prescribing this exercise in strength training and rehabilitation programs.

Effects of dietary fish oil on thyroid hormone signaling in the liver.

n-3 polyunsaturated fatty acids (PUFAs) present in fish oil (FO) potently decrease serum lipids, which is also an effect of thyroid hormones. Both PUFAs and thyroid hormones affect hepatic lipid metabolism, and here we hypothesized that a long-term diet rich in n-3 PUFAs would enhance thyroid hormone action in the liver. Female rats received isocaloric and normolipid diets containing either soybean oil (SO) or FO during lactation. Male offspring received the same diet as their dams since weaning until sacrifice when they were 11 weeks old. FO group, as compared to SO group, exhibited lower body weight since 5 weeks of age until sacrifice, with no alterations in food ingestion, lower retroperitoneal white fat mass and elevated inguinal fat mass relative to body weight, with unchanged water and lipid but reduced protein percentage in their carcasses. FO diet resulted in lower serum triglycerides and cholesterol. Serum total triiodothyronine, total thyroxine and thyrotropin were similar between groups. However, liver thyroid hormone receptor (TR) ß1 protein expression was higher in the FO group and correlated negatively with serum lipids. Liver 5'-deiodinase activity, which converts thyroxine into triiodothyronine, was similar between groups. However, the activity of hepatic mitochondrial glycerophosphate dehydrogenase, the enzyme involved in thermogenesis and a well-characterized target stimulated by T3 via TRß1, was higher in the FO group, suggesting enhancement of thyroid hormone action. These findings suggest that the increase in thyroid hormone signaling pathways in the liver may be one of the mechanisms by which n-3 PUFAs exert part of their effects on lipid metabolism.