2015 ISAKOS Biennial Congress ePoster #2615
Selective Muscle Activation of Medial Vs. Lateral Hamstring Components
Kristin Briem, PT, PhD, Reykjavík ICELAND
Andri Helgason, PT, Reykjavík ICELAND
Arnar Már Kristjánsson, PT, Reykjavík ICELAND
Gunnlaugur Jónasson, PT, Reykjavík ICELAND
Thorsteinn Ingvarsson, PT, Reykjavík ICELAND
University of Iceland, Reykjavík, ICELAND
FDA Status Not Applicable
Summary: Electromyography, registering relative activation levels of hamstring muscle components, demonstrated that combining active or passive medial vs. lateral tibial rotation with knee flexor activities selectively activates medial vs. lateral hamstring components, respectively.
Hamstring injury may lead to selective inhibition and/or atrophy of the injured muscle component. Post-injury deficits may not be recovered with generalized hamstring rehabilitation strategies. This may lead to compensation by other components or prolonged strength deficits with possible greater risk of re-injury to the index limb. Rehabilitation strategies that selectively influence the ratio of medial vs. lateral hamstring activation levels may more specifically target the injured component, thereby reducing the risk of residual strength deficits and/or risk of re-injury. The purpose of the study was to assess the influence of tibial rotation on medial and lateral hamstring muscle activation levels and isometric knee flexor strength measures in healthy young adults.
Forty healthy young men and women, aged 18-31, were recruited for the study. The effect of medial (MR) vs. lateral (LR) rotation of the tibia during knee flexor activities was investigated by using electromyography to measure activation levels of semitendinosus (ST) and biceps femoris (BF). Data were obtained during performance of two exercises: a) the Nordic hamstring exercise (NH), using passive rotations of the tibia, and b) seated maximal isometric knee flexion of the right lower limb, incorporating volitional rotations of the tibia. Peak signals were normalized to those obtained during a standardized isometric contraction in prone at 25° knee flexion. Analysis of variance was used for statistical testing, with alpha set at 0.05.
A significant interaction was found during performance of the NH (p<0.001) due to preferential activation of BF during LR vs. MR of the tibia while the rotations had a negligible effect on ST. In addition, an interaction was found, reflecting greater rotation dependent differences in ST and BF activation levels of the right limb during the isometric test compared to the NH (p=0.012). Calculated ratios of relative ST/BF activation levels were 117% vs. 105% with MR and LR during NH, while the respective values were 132% vs. 96% during isometric testing.
Strategies including passive and/or volitional tibial rotation with general hamstring training should be considered in cases where specific medial vs. lateral components need to be targeted during rehabilitation. Standardizing tibial rotation during testing of knee flexor strength is important, as this influences the outcome measure and is relevant for inter-limb comparisons and when monitoring progress over time.