Trunk muscle coordination in walking and running

by Steve Saunders and Paul Hodges

(Steve Saunders, senior practitioner and director of Saunders Sport and Spinal, Adelaide, has worked with the Australian track and field team. Co-author Paul Hodges is with the Prince of Wales Medical Research Institute in Sydney and the University of Queensland)

Poor neuromuscular control of the lumbo-pelvic complex is believed by clinicians to contribute often to the onset of or incomplete recovery from injuries of the spine [1], pelvis [2] and lower leg [3].

This belief has until recently been based primarily on anecdotal evidence and biomechanical models that present coordinated movement of the lumbo-pelvic complex as being fundamental to efficient movement and postural control [4].

Recent behavioural investigations of deep and superficial trunk muscle activity during non-functional tasks have demonstrated an association between trunk muscle coordination and low back pain [5] and improved our understanding of the trunk motor strategies underlying lumbo-pelvic stability.

These studies have demonstrated a functional differentiation between deep and superficial trunk muscles and highlighted the contribution of transversus abdominis (TrA) [6], diaphragm (D) [7], the pelvic floor musculature (PFM) [8] and Multifidus (M) [9] to intersegmental stability of the lumbo-pelvic complex.

While they have also demonstrated concurrent postural and respiratory activation of the TrA and D, they have found the postural activation of these muscles to be compromised during relatively simple tasks when the respiratory load is increased.

Recently, a series of studies was undertaken to investigate the coordination of deep and superficial trunk muscles during a more functional and complex task in locomotion.

Previous investigations of trunk muscle activity during locomotion had not investigated deep lumbo-pelvic musculature (TrA, D, MD and PFM).

EMG recordings of deep (TrA and deep multifidus (MD)) and superficial (obliquus internus (OI) obliquus externus (OE), rectus abdominis (RA), superficial multifidus (MS) and erector spinae (ES)) trunk muscle activity during walking (1ms-1 and 2ms-1) and running (2ms-1, 3ms-1, 4ms-1, 5ms-1) were made from asymptomatic, recreationally active subjects.

Fine-wire electrodes were inserted with ultrasound guidance. Gait cycle parameters and lumbo-pelvic kinematics were recorded using the Vicon three dimensional motion analysis system. An inductance plethysmograph was used to record respiratory movement of the ribcage.

Data confirm tonic activation of TrA during walking and running to a threshold of 3ms-1. In contrast, the remaining trunk muscles demonstrated phasic activation.

A change in locomotor mode was associated with a change in timing of OE and OI peak EMG amplitude and lumbo-pelvic rotation in the transverse plane. RA and the paraspinals increased the percentage of the gait cycle for which they were active with increases in running speed until all trunk muscles were phasically active for 70% - 86% of the gait cycle during running at 5ms-1.

Respiratory modulation of TrA, OI and OE was present (greatest for TrA.) and shown to be reduced with increasing locomotor speed.

Results are consistent with the contribution of (1) TrA to intersegmental stabilisation of the spine and support of the abdominal contents during locomotion and (2) the contribution of superficial trunk muscles to the control of lumbo-pelvic motion.

Furthermore, it appears that the trunk motor system prioritises trunk muscle function depending upon the nature of the postural and respiratory demands placed upon it.

The use of techniques to cognitively retrain deep muscle function to restore intersegmental stability of the lumbo-pelvic complex and subsequent progression to functional, context specific training appears logical. Moreover, the potential for spinal stability, torque production, respiration and athletic performance to be compromised in the presence of inappropriate trunk motor strategies is highlighted.

References:
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