Modified vector coding analysis of trunk and lower extremity kinematics during maximum and sub-maximum back squats

https://doi.org/10.1016/j.jbiomech.2020.109830Get rights and content

Abstract

The back squat is a complex movement with significant demands on the lower extremities and trunk to raise an external load. The back squat is simultaneously an open and closed kinetic chain movement that requires coordination of the entire body for successful completion of the lift. Therefore, this study aimed to examine coordination of the thigh and shank, trunk and thigh, and the hip and knee during the concentric phase of maximum, supra-maximum (at 105% max), and sub-maximum (at 80% max) back squats. Fourteen resistance trained adults participated in this study. Maximum back squat loads were determined using a previously determined progressive load protocol. Motion capture of the trunk and lower extremities and ground reaction force data were recorded during all squats. Angle-angle plots and modified vector coding were performed to analyze segment and joint coupling angles and knee-hip moments. Overall, the concentric phase of back squats depict a transition from early knee dominance to hip dominance as the system ascends. Interestingly, all squats presented with coupling of thigh-rising and trunk-falling. Based on the angle-angle plots and the modified vector coding results, the prolonged coupling of trunk falling and thigh rising likely resulted in too large of a moment arm for the external load for the participants to overcome during Supramax conditions.

Introduction

The squat is a highly utilized, multi-joint resistance training exercise that requires coordinated efforts spanning the trunk, pelvis, and lower extremity musculature. The loads for the hip and knee joints comprise 80–90%, whereas the ankle contributes 0–20%, of the total lower extremity moment to lift the system mass during the upward (concentric) portion of back squats (Escamilla, 2001, Flanagan et al., 2015, Flanagan and Salem, 2008, Fry et al., 2003, Hirata and Duarte, 2007, Lorenzetti et al., 2012). Previous research has delineated the concentric (upward) portion of the back squat into three distinct regions: Acceleration, when vertical bar velocity is increasing from zero to peak positive, Sticking/Failure Region, vertical velocity decreases to a local minima, and finally the Strength and Deceleration Region which ends when the person is fully standing erect (Escamilla et al., 2000). The “Sticking Region” has garnered a great deal of attention, as research aims to understand how the body overcomes the external resistance (Bryanton et al., 2012, Kubo et al., 2018), leading to a success instead of failure (Kompf and Arandjelović, 2017, Kompf and Arandjelović, 2016, van den Tillaar, 2015, van den Tillaar et al., 2014). Failure of a maximum load back squat is most frequently blamed on physiological parameters (Cramer et al., 2015, Duncan et al., 2014, Eslava et al., 2006, Mathew et al., 2016). Largely, discrete variables have been the focal point of biomechanical assessments of the back squat. However, there is no consensus within the current literature of a primary/singular cause of failure to complete back squats. For example, Yavuz, et al. identified a slightly more forward trunk lean in a 1RM back squat compared to a 90% 1RM back squat, while muscle activation at both conditions were not different in any lower extremity muscle observed (Yavuz and Erdag, 2017). However, van den Tillaar, et al. identified decreased biceps femoris and increased soleus muscle activation between the Acceleration and Sticking Regions of a maximum back squat (van den Tillaar et al., 2014). Van den Tillaar et al. also found increased rectus femoris and decreased gluteus maximus muscle activation between the Acceleration and Sticking Regions in a follow-up study, with no differences in the biceps femoris (van den Tillaar, 2015). Escamilla, et al. hypothesized that the decrease in vertical velocity creates an insurmountable resistance that the muscles are unable to overcome (Escamilla et al., 2001). Based on the lack of unanimous results of the current literature, there is a need for further research examining factors that impact maximum/supramaximum lifts.

Although a vast majority of previous literature has described back squats using discrete variables (Escamilla, 2001, Escamilla et al., 2001, Kritz et al., 2009, Schoenfeld, 2010), an analysis of the trunk/lower extremities as a coordinated functional unit has yet to be attempted (i.e. dynamical systems approach). The dynamical systems approach recognizes that the human body is a complex system with many components that influence movement and incorporates that understanding into evaluation (Glazier et al., 2003). Analyses of joint/segment coordination, a subset of dynamical systems, has advanced our understanding of movement in multiple areas, including running injuries (Hamill et al., 2012, Heiderscheit et al., 2002), increasing speeds (Hafer and Boyer, 2017), anticipated/unanticipated dynamic tasks (Weir et al., 2019), and the injury susceptibility during landings (DiCesare et al., 2019). Considering the back squat requires complex interactions between the joints/segments of the lower extremities and trunk, a dynamical systems approach could elicit further insights into the coordination required for success with maximal loading.

Angle-angle plots allow for examinations of the coupling of segments between limbs, between segments or within a segment. Modified vector coding has been implemented to analyze coordination of joints and segments during different movement patterns (Hamill et al., 2012). For example, vector coding has been used to analyze intra-limb coordination (Needham et al., 2015) during cutting maneuvers (Samaan et al., 2015), coordination variability (Ferber et al., 2005, Miller et al., 2010), and inter-segment coordination (Chang et al., 2008, Needham et al., 2014). Although back squats are quite different from the previous analyses, joint coupling should likely exist given the need for simultaneous extension of the hip, knee, and ankle joints to raise the trunk/weight and lower extremities during the upward phase (Escamilla et al., 2001). Thus, a technique such as modified vector coding could be useful for analyzing the complex coordination patterns during back squats.

Therefore, the purposes of this study were to 1) describe coupling of the shank and thigh, thigh and trunk, and knee and hip and 2) present the effects of bar load on segment and joint coupling during the concentric phase of back squats. We hypothesized that 1) both thigh-trunk movements and knee-hip movements would be uncoupled during the Sticking Region, demonstrating a heavy focus on raising the trunk and hips and 2) segment and joint uncoupling would increase with greater bar loads.

Section snippets

Participants

This study was approved by the Institutional Review Board. Fourteen healthy adults (Table 1) were recruited to participate in this study. To be included in this study, participants had to be 18–55 years, have no history of knee injuries, have at least one-year experience back squatting at or near maximal loads, and have performed weighted squats at least one-day per week. Exclusion criteria included any lower extremity injuries in the past three months, knee pain in the past six months, a

Results

Statistical significance level was reached for the overall MANOVA (F = 6.79, p = 0.011; ηp2 = 0.982). Reports from statistically significant within-subjects ANOVAs are provided in Table 2.

Discussion

During the dynamic movement provided by the back squat, the shank and thigh act in a closed chain manner, while the trunk is free to move as an open chain segment. While our first hypothesis was supported (thigh-trunk and knee-hip were not coupled during Sticking Region), our second hypothesis was only partially supported. Increased loads demonstrated coupled thigh rising and trunk falling, whereas the Submax condition was almost completely focused on thigh-rising only during the Sticking

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

References (44)

  • Y. Benjamini et al.

    Controlling the false discovery rate: A practical and powerful approach to multiple testing

    J. R. Stat. Soc. Ser. B

    (1995)
  • H.J. Bennett et al.

    Frontal plane tibiofemoral alignment is strongly related to compartmental knee joint contact forces and muscle control strategies during stair ascent

    J. Biomech. Eng.

    (2018)
  • M. Bryanton et al.

    Effect of squat depth and barbell load on relative muscular effort in squatting

    J. Strength Cond. Res.

    (2012)
  • G.K. Cole et al.

    Application of the joint coordinate system to three-dimensional joint attitude and movement representation: A standardization proposal

    J. Biomech. Eng.

    (1993)
  • J.T. Cramer et al.

    Muscle activation during three sets to failure at 80 vs. 30 % 1RM resistance exercise

    Eur. J. Appl. Physiol.

    (2015)
  • P. Davis

    Errors of numerical approximation for analytic functions

    J. Ration. Mech. Anal.

    (1953)
  • C.A. DiCesare et al.

    Sport specialization and coordination differences in multisport adolescent female basketball, soccer, and volleyball athletes

    J. Athl. Train.

    (2019)
  • M.J. Duncan et al.

    The effect of sodium bicarbonate ingestion on back squat and bench press exercise to failure

    J. Strength Cond. Res.

    (2014)
  • R.F. Escamilla

    Knee biomechanics of the dynamic squat exercise

    J. Am. Coll. Sport. Med.

    (2001)
  • R.F. Escamilla et al.

    A three-dimensional biomecahnical analysis of the squat during varying stance widths

    Med. Sci. Sports Exerc.

    (2001)
  • R.F. Escamilla et al.

    A three-dimensional biomechanical analysis of sumo and conventional style deadlifts

    Med. Sci. Sports Exerc.

    (2000)
  • J. Eslava et al.

    Differential effects of strength training leading to failure versus not to failure on hormonal responses, strength, and muscle power gains

    J. Appl. Physiol.

    (2006)
  • Cited by (0)

    View full text