The influence of muscle activation on impact dynamics during lateral falls on the hip
Introduction
Hip fractures are a widespread and severe health concern for older adults, with frequency estimates of up to 21 million globally per year by 2050 (Cummings and Melton, 2002). As the risk of hip fracture is directly related to the loads applied to the proximal femur (Tamura et al., 1982), increased knowledge of the factors that influence impact dynamics of the pelvis/femur system could assist with development of interventions aimed at hip fracture prevention.
While recent studies are advancing our understanding of dynamics of the pelvis and proximal femur system during lateral impacts (Bhan et al., 2014, Choi et al., 2014, Laing and Robinovitch, 2010, Sarvi and Luo, 2015) there remain questions about the role of muscle activation on these dynamics. Muscle activation has been demonstrated to play a role in impact dynamics across a breath of scenarios including running, car impacts and head impacts (Laing and Robinovitch, 2010, Newell et al., 2013, Nigg and Liu, 1999, Sarvi and Luo, 2015, van der Horst et al., 1997). Specific to fall-related injuries, Burkhart and Andrews (2013) studied falls onto outstretched hands, and observed significant increases in activation levels of six upper limb muscles between release, start of impact, and moment of peak impact force. However, little research has examined the potential influence of muscle activation on dynamics of the femur-pelvis system during the impact phase of sideways falls. Charactization of activation patterns during lateral falls on the hip could assist in determining the potential importance of including muscle activation into computational models of hip fracture risk.
There are several potential mechanisms by which muscle activation might affect impact dynamics. First, since activation increases local muscle longitudinal stiffness (Tamura et al., 1982), it is possible that this effect translates into increased overall stiffness within the femur/pelvis system. Similarly, co-contraction of antagonistic muscles may serve to increase joint rotational stiffness. Second, muscle activation may influence the effective mass of the pelvis, and ultimately, the inertia involved in the event of a fall-related hip impact. Finally, it is possible that muscular contractions could change the geometry of the body-impact surface interface, potentially influencing load distribution and resulting impact dynamics. There exists some limited literature that provides insights into these issues. While muscle activation of the gluteal muscles has been found to change thickness of the tissues overlying the ischial tuberosity (Hodges et al., 2003, Makhsous et al., 2011), similar effects have not been observed for the region overlying the greater trochanter (GT) (Tamura et al., 1982), attributed in part to the GT’s use as an attachment point for multiple tendinous tissues as opposed to muscle bodies. While Choi et al. report that increased activation of hip abductor muscles decreased peak femoral neck compressive stress by 24% and tensile stress by 56% during simulated sideways falls, these results may not be generalizable as they were generated with a mechanical test system (Choi et al., 2014). In the most direct studies of the influence of muscle activation on impact dynamics, Robinovitch et al. (Robinovitch et al., 1991, Sarvi and Luo, 2015) used pelvis release experiments with live volunteers. They initially reported that impact peak force applied to the proximal femur increased with increased muscle activation (Robinovitch et al., 1991), but found little effect of muscle activation in a subsequent study (Sarvi and Luo, 2015). This lack of consistency could potentially be related to their approach of simply asking participants to “contract [their] trunk and back muscles prior to the start of each ‘contracted state’ trial” (i.e. muscle activation level was not explicitly controlled). Overall, despite plausible mechanisms by which muscle activation could influence impact dynamics during falls on the hip, there is currently no available literature that characterizes activation patterns during the impact phase of sideways falls, or the influence of explicit changes in activation magnitude on impact dynamics.
The effects of muscle activation on impact dynamics could differ across sexes due to differences in body composition. Previous studies have shown that the thickness of soft tissue overlying the greater trochanter is negatively correlated with estimated mechanical risk of hip fracture during a fall on the hip (Majumder et al., 2008, Robinovitch et al., 1995). Compared to males, females have significantly less lean tissue mass, increased fat mass, and a greater proportion of their fat mass located in the lower body (Ley et al., 1992). More local to the proximal femur, females have significantly more soft tissue overlying the greater trochanter when compared to males (Ley et al., 1992, Majumder et al., 2013). However, whether these differences in body composition interact with muscle activation to influence impact dynamics during sideways falls on the hip is unknown. Given the increased incidence of hip fractures in females (Jean et al., 2013), enhanced knowledge of these factors could provide support for the use of gender-specific computational models of pelvic impacts that incorporate muscle activation contributions (Jean et al., 2013).
The objectives of this study were two-fold. The primary goal was to investigate the potential effects of targeted muscle activation magnitude on impact dynamics during low energy falls on the hip with human volunteers. Our first hypothesis was that trials with contracted muscles would produce (a) higher peak force, (b) shorter time to peak force, and (c) increased stiffness of the femur-pelvis system (henceforth referred to as pelvic stiffness). Our second hypothesis was that more pronounced effects of muscle activation would be observed for males compared to females. The study’s secondary goal was to characterize time-varying changes in muscle activation magnitude during the baseline ‘muscle relaxed’ conditions to provide insights into naturally occurring activation profiles during lateral impacts of the femur-pelvis complex.
Section snippets
Participants
Fifteen university aged participants (mean (SD) age = 21.7 (3.2) years) participated in this study. Seven participants were male (mass = 76.8 (7.4) kg; height = 180.0 (6.4) cm; age = 23.0 (2.9)) and eight were female (mass = 62.1 (10.4) kg; height = 168.4 (7.8) cm; age = 20.6 (3.2)). Exclusion criteria included any history of pelvis, femur or spine fractures, history of easily invoked bruising, or any other health conditions that may have been aggravated by the experimental protocol. All
Results
Fmax was significantly affected by a main effect of muscle activation state with values, on average, 78 N (9.3%) higher during contracted trials (F = 6.798, p = .022; Table 1; Fig. 3). Despite mean female values being 10.8% lower, Fmax was not significantly different between males and females (F = 0.400, p = .538; Table 1; Fig. 3). Furthermore, Fmax was not associated with any significant interaction effects between independent variables (Table 1).
Tmax was associated with a significant
Discussion
This study investigated the potential effects of targeted muscle activation magnitude on impact dynamics during low energy falls on the hip. Our first hypothesis was partially supported as activation state had a main effect on Fmax across sexes and release heights, with values (on average) 78 N (9.3%) higher during contracted trials. However, contrary to our second hypotheses, the effects of muscle activation on Tmax and kp were more pronounced in females. Specifically, while males displayed
Acknowledgments
This research was funded in part by an operating grant from the Natural Sciences and Engineering Research Council of Canada (grant # 386544), an infrastructure grant from the Canadian Foundation for Innovation, and infrastructure and Early Career Research Award grants from the Ontario Ministry of Research and Innovation.
Conflict of interest statement
The authors have no conflicts of interest to declare. No persons other than the authors had input into any aspect of the study including research question development, study design, data analysis, interpretation of results, or manuscript writing.
References (27)
- et al.
Energy absorption during impact on the proximal femur is affected by body mass index and flooring surface
J. Biomech.
(2014) - et al.
Kinematics, kinetics and muscle activation patterns of the upper extremity during simulated forward falls
J. Electromyogr. Kinesiol.
(2013) - et al.
Epidemiology and outcomes of osteoporotic fractures
Lancet
(2002) - et al.
Reducing hip fracture risk during sideways falls: evidence in young adults of the protective effects of impact to the hands and stepping
J. Biomech.
(2007) - et al.
Characterizing the effective stiffness of the pelvis during sideways falls on the hip
J. Biomech.
(2010) - et al.
Sex- and menopause-associated changes in body-fat distribution
Am. J. Clin. Nutr.
(1992) - et al.
Effects of trochanteric soft tissue thickness and hip impact velocity on hip fracture in sideways fall through 3D finite element simulations
J. Biomech.
(2008) - et al.
Neck posture and muscle activity are different when upside down: a human volunteer study
J. Biomech.
(2013) - et al.
The effect of muscle stiffness and damping on simulated impact force peaks during running
J. Biomech.
(1999) - et al.
Contribution of trochanteric soft tissues to fall force estimates, the factor of risk, and prediction of hip fracture risk
J. Bone Miner. Res.
(2007)
Predicting the effects of muscle activation on knee, thigh, and hip injuries in frontal crashes using a finite-element model with muscle forces from subject testing and musculoskeletal modeling
Stapp Car Crash J.
Effects of hip abductor muscle forces and knee boundary conditions on femoral neck stresses during simulated falls
Osteoporos. Int.
The factor-of-risk biomechanical approach predicts hip fracture in men and women: the Framingham Study
Osteoporos. Int.
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