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ndounskaia75
11-17-2008, 10:26 AM
I strongly believe that application of the leading joint hypothesis (LJH, Dounskaia 2005, Exp Brain Res, 166:1-16) would help to understand in detail the role of gravity, ground reaction forces, and muscular control in running. Zajac and colleagues suggested that during complex movement, each muscle can perform one of three functions, generation, transfer, or absorption of power. The LJH further specifies the role of various muscles during multi-joint movements. Namely, it states that the function of motion generation is limited to a single ("leading") joint (or, in some cases, a joint linkage spanned by bi-articular muscles). This joint is determined by its advantage in exploiting a mechanical effect driving the motion. The role of musculature at other joints is to regulate passive motion caused at them by motion-dependent (interaction) torques and external forces. We call these joints "subordinate" joints.



I have never had a chance to apply the LJH to locomotion. However, my guess is that during the stance phase, the ankle should be the leading joint responsible for generation of movement energy. It is quite possible that the ankle is used to propel the center of gravity forward to let gravitation to do the major work, as suggested by Romanov and Fletcher (2007). The role of the knee and hip muscles would be to regulate the effect of ankle motion. The goal of this regulation would, most probably, be balance maintenance. It may also be leg extension, but likely not to propel the body but rather to prepare the leg for its flexion that will be needed to soften the impact with the ground at the beginning of the next stance period.



I would expect that the analysis required to distinguish the leading and subordinate joints and the exact role of each is relatively simple, not like simulations performed by Zajac and colleagues. All torque components (muscle, interaction, gravitation torque, and torque caused by ground reaction forces) would need to be computed at each joint, and then the contribution of each to net torque would need to be analyzed, as we have been doing it for arm movements. Our studies show that this method helps to understand the global organization of control, the role of each joint in it, as well as subtle changes in joint control caused by aging or Parkinson's disease. Other authors have exploited this type of analysis to study differences in piano stroke performed by novice and expert pianists (Furuya & Kinoshita, 2008, Neuroscience, 156:390-402). Applied to running, this approach may be able to reveal differences in joint control between fast and slow runners and between different running techniques.



If anybody is interested to run this analysis, I would be happy to collaborate.



Natalia Dounskaia

Movement Control and Biomechanics Lab

Arizona State University

Natalia.dounskaia@asu.edu


________________________________

From: * Biomechanics and Movement Science listserver on behalf of Nick Brown
Sent: Thu 11/13/2008 10:08 PM
To: BIOMCH-L@NIC.SURFNET.NL
Subject: [BIOMCH-L] Pose Running



We were interested in the recent post on Pose running and would like to try and spark a discussion on the topic. In no way are we trying to support or discount the possibility that the Pose method improves running technique by increasing speed or reducing injury.

In Dr Romanov's discussion paper on the Pose running technique (Romanov and Fetcher, 2007, Sport Biomechanics, 6, pp434-452), the authors state that they "hope to establish theoretically that gravity is the motive force in running...". The paper then argues from this perspective that other motive forces such as from muscles are relatively unimportant. The forces that act on the human body in motion include; (i) motion-dependent forces (from Coriolis and inertial effects), (ii) internal forces (principally from muscle), (iii) external forces (from ground, wind etc), and (iv) forces due to gravitational acceleration. Well-coordinated movement has also been shown to be characterized by the ability to adjust muscular forces to account for or to take advantage of motion-dependent, gravitational and external forces (e.g. Hollerbach et al 92; Schneider et al, 89 & 90; Ulrich et al 94). Running is likely no different from other well-coordinated body movements in that the runner or mover must account for and exploit the force environment in which they find themselves.

While gravitational acceleration might be particularly important in running, the external, motion-dependent and muscular forces can not be discounted as contributing to forward acceleration of the body. Zajac, Neptune and Kautz (2002, Gait and Posture, 17, pp1-17) review nicely how forward trunk acceleration receives marked contributions from lower extremity muscles, at least in walking. Romonov and Fetcher (2007) also state that extensor muscle activity ceases during mid stance and an extensor paradox arises. We have EMG on numerous good runners (national and international level) at running speeds of 6 to 9 m/s and we find ample EMG activity in late stance from muscle throughout the limb, including extensor muscles. Even without extensor muscles being active (which some are) forward acceleration of the trunk can arise from these 'non-extensor' muscles, although the magnitude of their contribution appears to be unknown for faster running.

It is certainly interesting to consider how good runners might exploit motion-dependent and gravitational forces (perhaps the Pose Technique promotes this), and how various muscles of the lower extremity contribute to the forward acceleration of the body's mass centre.

We would be interested in the thoughts of others.

Doug Rosemond, John Baker, Wayne Spratford, Alexi Sachlikidis, Sara Brice, Nick Brown
Department of Biomechanics and Performance Analysis
Australian Institute of Sport
Canberra, Australia


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