Energy redistribution analysis of dynamic mechanisms of multi-body, multi-joint kinetic chain movement during soccer instep kicks

Abstract

The purpose of this study is to develop a model to analyze energy redistribution mechanisms of a multi-joint limb system and to examine the mechanisms underlying the production of the mechanical energy of the system during instep kicking. Kicking movements of 11 collegiate soccer players were recorded using a motion capture system, and ground reaction force during kicks was measured. Using the experimental data and the state-space power analysis developed in the current study, the kinetic energy change of the modeled segments was decomposed into causal components due to various dynamic factors (muscular and non-muscular interactive moments). The results showed that the increase of the kinetic energy of the kicking limb resulted from the energy transfer mechanisms between the decelerated segment (a proximal segment) and accelerated segment (a distal segment), induced by a non-muscular interactive moment due to the external joint force or the centrifugal force. The proximal (thigh) to distal (shank) sequential motion pattern observed was due to the energy transfer mechanism induced by the centrifugal effect acting to accelerate the shank and decelerate the thigh. The fact suggests that effective use of that mechanism may be advantageous to enhance the kinetic energy of the kicking shank. In conclusion, energy transfer mechanisms likely play a greater role in dynamic kicking than muscle power output, and better coordination to exchange kinetic energy among segments makes kicking more efficient.

Introduction

Many kinds of swinging movements in sports, such as soccer instep kicking, baseball pitching, golf swing and other swing movements usually aim to produce the highest speed of the distal endpoint (kicking foot, throwing hand and ball, and club head) of the linked segment system. The underlying mechanisms of how skilled players generate the dynamic limb motion and enhance the distal endpoint speed successfully are of interest for researchers, coaches and athletes. In these dynamic swinging movements, the proximal to distal sequential pattern (P–D sequence) between participating segments or joints often occurs. This sequential motion is considered advantageous when increasing the distal endpoint speed (Kreighbaum & Barthels, 1999).

In the case of the kicking leg motion during an instep kick, forward rotation of the proximal thigh (primarily relating to the hip joint flexion) precedes forward rotation of the distal shank (primarily relating to the knee joint extension), and subsequently the shank rotates forward while the forward rotation of the thigh slows down before impact with the ball (Lees & Noran, 1998). It was found that such a kinematic pattern in the kicking thigh and shank motions is a result not only of the joint moment acting at the proximal end of the segment (the muscular moment) but also of the motion-dependent interactive moment due to adjacent segmental rotation (Putnam, 1991, Putnam, 1993). Previous studies showed that motion-dependent moment could contribute to the production of a P–D sequential motion pattern between the kicking thigh and shank (Apriantono et al., 2006, Dörge et al., 2002, Dörge et al., 1999). Additionally, our previous study that examined kicking movement using the multi-joint kinetic chain model found that the rapid kicking knee extension just before ball impact is a result of complex dynamic factors due to multi-joint rotations, including the kicking leg and non-kicking leg (supporting leg) joints as well as the external ground reaction force or moment acting on the kicking body (Naito, Fukui, & Maruyama, 2010). Analysis of calculated motion-dependent moments is helpful to investigate how much muscular and non-muscular moment (defined as an interactive moment due to joint rotations, external forces and moments acting on the kicker’s body) contributes to dynamic limb motion. However, the analysis of motion-dependent moments contribution to segmental or joint motion does not enable us to understand the kicking mechanisms completely, because that analysis has methodological limitations. Despite the concept that the P–D sequential motion in kicking could be represented as an exchange of mechanical energy from the thigh to the shank (Lees & Noran, 1998), kinetic modeling developed in the previous studies has not confirmed it by calculation of energy transferring among the segments. Consequently, the question of whether the P–D sequential kicking motion would be actually more efficient than when it is not exhibited has not been answered in full from the kinetic analysis used in the previous studies.

Joint motions normally result from moments generated by muscles (muscular moment) across that joint. Because of dynamic coupling in a multi-joint limb system (for example, walking and two legged pedaling), muscular moment acting at a given joint indirectly contributed to other joint rotation and mechanical energy of a segment to which it is not attached, through intersegmental forces transferring energy among segments (Fregly and Zajac, 1996, Zajac, 2002, Zajac et al., 2002). Recent studies focused on such energy transfer mechanisms during complex human movements, and have found that the mechanical energy of any segment is transferred to other segments via intersegmental joint forces acting to accelerate and decelerate those segments (Zajac, 2002, Zajac et al., 2002). However, to our knowledge, no systematic attempt to investigate energy transfer mechanisms in kicking has been made in the literature. A state-space power analysis as presented by Fregly and Zajac (1996), which is a method to analyze the relationships between causal work (power) due to the muscular moment and mechanical energy (power) applied to the segment, is useful to identify important joint muscular moment with respect to energy source. In addition, such an analysis enables us to know how non-muscular moment transfers mechanical energy from one segment to another.

It is believed that P–D sequential motion between proximal and distal segments in the kicking leg represents an exchange of mechanical energy from the thigh to the shank (Lees & Noran, 1998). Because the concept of mechanical energy transfer from proximal to distal segments has not actually been confirmed, a model to explain energy transfer mechanisms accomplished in such a multi-joint system is required. In particular, the state-space power analysis is useful in providing an insight into the energy transfer mechanisms in kicking movement. The purpose of this study is two fold. The first is to develop a model of multi-joint kinetic chain movement to decompose the mechanical energy of the segments to causal components resulting from the muscular and non-muscular interactive moments. The second is to examine underlying mechanisms to produce the kicking leg kinetic energy with respect to energy redistribution mechanisms during instep kicking. In particular, we focus on whether P–D sequential motion actually results in transfer of mechanical energy between the proximal and distal segments.