Article

Lower Extremity Muscle Functions During Full Squats

School of Human Kinetics, University of Ottawa, Ottawa, ON, Canada.
Journal of applied biomechanics (Impact Factor: 0.98). 12/2008; 24(4):333-9.
Source: PubMed

ABSTRACT

The purpose of this research was to determine the functions of the gluteus maximus, biceps femoris, semitendinosus, rectus femoris, vastus lateralis, soleus, gastrocnemius, and tibialis anterior muscles about their associated joints during full (deep-knee) squats. Muscle function was determined from joint kinematics, inverse dynamics, electromyography, and muscle length changes. The subjects were six experienced, male weight lifters. Analyses revealed that the prime movers during ascent were the monoarticular gluteus maximus and vasti muscles (as exemplified by vastus lateralis) and to a lesser extent the soleus muscles. The biarticular muscles functioned mainly as stabilizers of the ankle, knee, and hip joints by working eccentrically to control descent or transferring energy among the segments during scent. During the ascent phase, the hip extensor moments of force produced the largest powers followed by the ankle plantar flexors and then the knee extensors. The hip and knee extensors provided the initial bursts of power during ascent with the ankle extensors and especially a second burst from the hip extensors adding power during the latter half of the ascent.

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Article: Lower Extremity Muscle Functions During Full Squats

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    • "Strength training exercises, such as squatting, present a similar kinematics to the hip and knee as the extension exercise performed on a Reformer apparatus. Squats are performed by flexing and extending the hip and knee simultaneously, producing extensor moments at both joints throughout the exercise, with the extensor moments increasing during joint flexion and decreasing during joint extension phases (Wretenberg et al., 1993; Escamilla et al., 1998; Robertson et al., 2008). "
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    ABSTRACT: Considering the kinematics of leg extensions performed on a Reformer apparatus, one would expect high activation of hip and knee extensor muscle groups. However, because of the bi-articular nature of some lower limb muscles, and the possibility to vary the direction of force application on the Reformer bar, muscles can be coordinated theoretically in a variety of ways and still achieve the desired outcome. Hence, the aim of this study was to determine the knee and hip moments during leg extensions performed on the Reformer apparatus and to estimate the forces in individual muscles crossing these joints using static optimization. Fifteen subjects performed leg extensions exercises on the Reformer apparatus using an individually chosen resistance. To our big surprise, we found that subjects performed the exercise using two conceptually different strategies (i) the first group used simultaneous hip and knee extension moments, (ii) while the second group used simultaneous hip flexion and knee extension moments to perform the exercise. These different strategies were achieved by changing the direction of the resultant force applied by the subject’s feet on the Reformer bar. While leg extensions on the Reformer apparatus have been thought to strengthen the hip and knee extensors muscles, our results demonstrate that patients can perform the exercise in a different and unexpected way. In order to control the hip and knee moments and achieve the desired outcome of the exercise, the direction of force application on the Reformer bar must be controlled carefully.
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    • "Taken out of context of the fossil record, our data would suggest that the enlarged GMAX was evolved for sprinting, climbing, and running. Other research has demonstrated that the GMAX is important for throwing, squatting, uphill walking, and lunges (Marzke et al., 1988; Isear et al., 1997; Ekstrom et al., 2007; Lay et al., 2007; Robertson et al., 2008; Oliver and Keeley, 2010). Identifying only one of these locomotion actions as providing the pressure for the derived GMAX would ignore its importance in numerous other locomotor tasks. "
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    ABSTRACT: It has been suggested that the uniquely large gluteus maximus (GMAX) muscles were an important adaptation during hominin evolution based on numerous anatomical differences between humans and extant apes. GMAX electromyographic (EMG) signals have been quantified for numerous individual movements, but not across the range of locomotor gaits and speeds for the same subjects. Thus, comparing relative EMG amplitudes between these activities has not been possible. We assessed the EMG activity of the gluteal muscles during walking, running, sprinting, and climbing. To gain further insight into the function of the gluteal muscles during locomotion, we measured muscle activity during walking and running with external devices that increased or decreased the need to control either forward or backward trunk pitch. We hypothesized that 1) GMAX EMG activity would be greatest during sprinting and climbing and 2) GMAX EMG activity would be modulated in response to altered forward trunk pitch demands during running. We found that GMAX activity in running was greater than walking and similar to climbing. However, the activity during sprinting was much greater than during running. Further, only the inferior portion of the GMAX had a significant change with altered trunk pitch demands, suggesting that the hip extensors have a limited contribution to the control of trunk pitch movements during running. Overall, our data suggest that the large size of the GMAX reflects its multifaceted role during rapid and powerful movements rather than as a specific adaptation for a single submaximal task such as endurance running. Am J Phys Anthropol, 2013. © 2013 Wiley Periodicals, Inc.
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    • "Taken out of context of the fossil record, our data would suggest that the enlarged GMAX was evolved for sprinting, climbing, and running. Other research has demonstrated that the GMAX is important for throwing, squatting, uphill walking, and lunges (Marzke et al., 1988; Isear et al., 1997; Ekstrom et al., 2007; Lay et al., 2007; Robertson et al., 2008; Oliver and Keeley, 2010). Identifying only one of these locomotion actions as providing the pressure for the derived GMAX would ignore its importance in numerous other locomotor tasks. "

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