Joint dynamics and intra-subject variability during countermovement jumps in children and adults
Introduction
The inherent variability of human movements depends on a number of biomechanical, environmental and task constraints (Bernstein, 1967). The characteristics of movement variability have been shown to be influenced by motor development and specific motor skill training (Harbourne and Stergiou, 2003, Newell and Vaillancourt, 2001, Preatoni et al., 2010, Wilson et al., 2008). According to the theory of Bernstein (Bernstein, 1967, Newell and Vaillancourt, 2001) and experimentally supported by Schneider and Zernicke (1989) and Schneider et al. (1989) advanced skill learning is associated with increased utilization of passive structures. This step of skill learning has also been linked to reduced energy expenditure (Sparrow and Newell, 1994, Sparrow and Newell, 1998) and increased movement variability (Wilson et al., 2008).
Vertical jumping like a countermovement jump is a whole body movement where the performance level is easily evaluated by jumping height (Kollias et al., 2004). Furthermore, variation in the performance can easily be assessed as the standard deviation or coefficient of variation calculated on the jumping heights across several jumps. By quantifying the movement pattern of individuals of good and poor jumping performance through kinematic and kinetic analysis, several studies have aimed to describe the characteristics of superior jumping technique (Floria and Harrison, 2013b, Laffaye et al., 2005, Lees et al., 2006, Vanezis and Lees, 2005). Superior countermovement jump performance in aerobic gymnastics girls (age between 4 and 8 years) has been shown to include a faster eccentric movement and a fast transition between stretching and shortening resolving in an effective concentric phase (Floria and Harrison, 2013b). Furthermore, higher ankle joint power and work has been associated with higher countermovement jump in adult male soccer players (Vanezis and Lees, 2005). Differences in the movement pattern have been observed in children of different maturation stages (Harrison et al., 2007, Meylan et al., 2012) and between adults and children in jumping (Floria and Harrison, 2013a). Thus, it could be speculated that adults utilize a more consistent and energy efficient movement pattern during countermovement jumps compared to children, which would be characterized by a smaller amount of variability in the joint moment components and greater segment energy transfer through joints.
Movement patterns have been quantified by inverse dynamics during whole body movements like walking, running, jumping, kicking and throwing (Belli et al., 2002, Morrison, 1970, Putnam, 1993, Ravn et al., 1999, Sorensen et al., 1996, Vanezis and Lees, 2005, Winter and Robertson, 1978). Through an alternative inverse dynamic calculation method Simonsen et al. (1997) could explain the inter-subject differences in lower limb joint moments by differences in the contributions from proximal and distal joint reaction forces and rotational inertia. This approach enables a detailed analysis of the joint dynamics into underlying components and has not previously been applied to jumping movements. Robertson and Winter (1980) proposed a method to evaluate the energy flow in or out of a segment through the adjacent joints. The method was applied to walking and the authors showed phase differences in the amount of energy entering and exiting the segments through their respective joints (Robertson and Winter, 1980).
The present study applied inverse dynamics analysis, modified inverse dynamics analysis and joint energy transfer analysis to investigate 1) lower limb joint work and lower limb joint energy transport during countermovement jumps and 2) the joint dynamics intra-subject variation during countermovement jumps in children and adults.
We hypothesize that 1) adults will produce more joint work and 2) more energy is transferred through the joint centres compared to children. Finally, we hypothesize that 3) adults will exhibit lower joint dynamics intra-subject variation compared to children.
Section snippets
Method
The kinematic and kinetic data analysed by the present study has been used for analysis of coordination pattern, jumping performance and variation in jumping performance in a previous study (Raffalt et al., 2016).
Results
The adults produced significantly higher eccentric and concentric work at the hip joint (p<0.001) and significantly higher eccentric work at the knee joint (p<0.001) compared to the children but no group difference was observed in the work produced at the ankle joint (Fig. 2).
During the eccentric phase both groups produced significantly more work at the knee joint compared to the hip and ankle joint. Furthermore, the hip joint work was significantly higher compared to the ankle joint work (p
Discussion
The present study aimed at investigating the lower limb joint dynamics and the intra-subject variation in the joint dynamics during multiple countermovement jumps in children and adults. The main results were a significantly higher eccentric and concentric work at the hip and significantly higher eccentric knee joint work in the adult subjects, partly confirming our first hypothesis. In contradiction to our first hypothesis no group difference was observed for the work produced at the knee
Conflict of interest
The authors declare no conflict of interest.
Acknowledgements
The authors would like to thank Louise Videbæk and Julie Elgaard Blok for their contribution during the data collection.
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