The responses of leg and trunk muscles to sudden unloading of the hands: Implications for balance and spine stability

Department of Kinesiology, School of Human Kinetics, University of Windsor, Windsor, ON, Canada N9B 3P4.
Clinical Biomechanics (Impact Factor: 1.97). 11/2003; 18(9):812-20. DOI: 10.1016/S0268-0033(03)00167-0
Source: PubMed


Objective. To examine the anticipatory and responsive actions of leg and trunk muscles, and their role in whole-body and spine control in situations of sudden unloading of the hands in the sagittal plane. Design. EMG and force plate measures were used to determine the baseline, anticipatory responses and post unloading responses of selected trunk and leg muscles under different conditions of unload timing knowledge. Background. Postural muscles have been observed to increase activation in anticipation of a known loading situation to decrease the overall effect of an impulsive load delivered to the spine. It is thought that this increased activation places the spine in a more stable state, thereby reducing the likelihood of injury. Comparisons have not been made previously of the responses of postural muscles to unloading conditions where the certainty of unload timing is varied. Methods. Eleven male subjects, holding a 6.8 kg load in the hands, were subjected to three different unloading conditions: (1) voluntary load drop; (2) known timing of load release; (3) unknown timing of load release. Anterior-posterior center of pressure data, as well as EMG activity on 8 right side muscles, were collected for 10 trials in each condition. Results. Anterior-posterior center of pressure responses were significantly different (P < 0.05) between each of the three conditions. Lumbar erector spinae and thoracic erector spinae significantly decreased anticipatory activity as knowledge of the unload timing increased. Five of the eight monitored muscles demonstrated significantly decreased response levels as knowledge of the timing of unloading increased. Conclusions. When an unload is self-triggered, preparatory adjustments can be made which reduce the overall postural perturbation to the body, and the spine in particular, while minimizing the responsive activity of trunk muscles.

Download full-text


Available from: Jim R Potvin,
  • Source
    • "Compared to the subjects without LBP, this can be manifested as delayed actions of trunk muscles to sudden mechanical perturbation also termed postural reflex responses (PRRs) of the trunk (Boudreau et al., 2011; Cholewicki et al., 2005; Radebold et al., 2001). Trunk PRRs are most often evoked by perturbations applied to the trunk (Cholewicki et al., 2005; Radebold et al., 2000, 2001) or to the hands (Brown et al., 2003; Gregory et al., 2008; van der Burg et al., 2000). Furthermore most of the authors are assessing neurophysiological properties using electromyography while some studies are focusing on mechanical properties of PRRs (Hendershot et al., 2012; Reeves et al., 2014). "
    [Show abstract] [Hide abstract]
    ABSTRACT: It has been reported that altered neuromuscular control of the trunk is associated with lower back pain. In this context reflex delays of the trunk muscles have often been assessed but the reliability of the tests has not been well established. The aim of this study was to test the reliability of measuring reflex delays of the trunk muscles after two types of postural perturbations. 24 Healthy subjects participated in the intra-session study and 13 of them repeated the test protocol within 1-3 weeks, to determine inter-session reliability. Postural reflex delays to unexpected loading and unloading of the arms were assessed in a standing unrestrained position. Each subject performed 40 trials of each test in order to evaluate muscle responses of 5 trunk muscles using surface electromyography. Overall reliability increased with higher number of the averaged trials. Good intra-session (ICC3,1>0.75) and moderate (ICC3,1>0.60) inter-session reliability were reached in most of the monitored trunk muscles. Within the performed number of trials we did not observe any significant systematic intra- or inter-session bias effect. Averaging a higher number of consecutive trials would be recommended in future research and clinical practice.
    Journal of Biomechanics 06/2014; 47(11). DOI:10.1016/j.jbiomech.2014.05.024 · 2.75 Impact Factor
  • Source
    • "The backward COP displacements in the AP direction were found in the symmetrical stance (PARA) and the staggered stance (RIGHT and LEFT) conditions. Similar anticipatory COP displacements in the backward direction were reported previously while describing body perturbations induced by self-initiated fast arm movements (Aruin and Latash 1995) and expected load release in standing (Brown et al. 2003; Shiratori and Aruin 2007) as well as when pointing in the sagittal plane while in sitting (Le Bozec and Bouisset 2004, 2009). Stance-related changes in the muscle activity in the legs also affected the COP displacement during the compensatory phase of postural control: the COP displacements were larger in staggered stance compared to parallel stance, and the difference was statistically significant only for the COP CPA1_AP . "
    [Show abstract] [Hide abstract]
    ABSTRACT: A number of occupational and leisure activities that involve pushing are performed in symmetrical or asymmetrical stance. The goal of this study was to investigate early postural adjustments (EPAs), anticipatory postural adjustments (APAs), and compensatory postural adjustments (CPAs) during pushing performed while standing. Ten healthy volunteers stood in symmetrical stance (with feet parallel) or in asymmetrical stance (staggered stance with one foot forward) and were instructed to use both hands to push forward the handle of a pendulum attached to the ceiling. Bilateral EMG activity of the trunk and leg muscles and the center of pressure (COP) displacements in the anterior-posterior (AP) and medial-lateral (ML) directions were recorded and analyzed during the EPAs, APAs, and CPAs. The EMG activity and the COP displacement were different between the symmetrical and asymmetrical stance conditions. The COP displacements in the ML direction were significantly larger in staggered stance than in symmetrical stance. In staggered stance, the EPAs and APAs in the thigh muscles of the backward leg were significantly larger, and the CPAs were smaller than in the forward leg. There was no difference in the EMG activity of the trunk muscles between the stance conditions. The study outcome confirmed the existence of the three components of postural control (EPAs, APAs, and CPAs) in pushing. Moreover, standing asymmetrically was associated with asymmetrical patterns of EMG activity in the lower extremities reflecting the stance-related postural control during pushing. The study outcome provides a basis for studying postural control during other daily activities involving pushing.
    Experimental Brain Research 06/2013; 228(3). DOI:10.1007/s00221-013-3567-4 · 2.04 Impact Factor
  • Source
    • "For example, it has been shown that loss of balance can be an important cause of back injury (Manning et al., 1984, 2000; Courtney et al., 2001; Davies et al., 2001). Suddenness (of exertion or movement)—caused, for example, by an unexpected load or a sudden release—has also drawn the attention of experimental studies (Andersen et al., 2001; Lavender et al., 1989; Commissaris and Toussaint, 1997); such events may cause an overreaction, producing an intense muscular contraction and a loss of balance (Brown et al., 2003; Chow et al., 2003, 2005). Nevertheless , it is difficult, for obvious ethical reasons, to study the impact of deviations experimentally. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The aim of the study was to analyze the narratives in accident files to document the circumstances of accidents in a beverage delivery company, in particular, in regard with the activities performed at the time of the accident and the deviations reported. A second aim was to understand the impact of the transformations introduced by the company on accident patterns. Narrative material from 546 files covering a 7-year period was analyzed. Special attention was given to collecting information on the activities conducted at the time of the accident, including location, foot support base, operation, and material involved. The analysis allowed specifying elements that have good potential for improving handling situations and decreasing accident risks. Three categories of deviation were analyzed: situations reported as particular or difficult, unforeseen events, and dysfunction reported in the activity itself. Results show that several external factors play an important role in the occurrence of accidents. Most of these factors are beyond risk analysis of handling situations. The impact of the transformations on the number, seriousness, and causes of accidents was dramatic. Analysis shows that current investigative risk tools are insufficient in helping management predict how decisions will affect safety. The discussion situates the results within the various theories of musculoskeletal mechanisms of injury.
    Safety Science 11/2012; 50(9):1792–1800. DOI:10.1016/j.ssci.2012.04.008 · 1.83 Impact Factor
Show more