Patterson, C.W. (2010)
REPEATABILITY OF GAIT MECHANICS WHEN USING AN ATHLETE SELF-SELECTED RUNNING VELOCITY
A Case Study of an 800m Runner
In studies of athlete’s gait, a common them is to investigate the effect of velocity alterations on mechanical variables using a standardised running velocity (Arampatzis et al., 1999; Karamanidis et al., 2004; Queen et al., 2006). Although a generally accepted method of gaining an accurate and appropriate interpretation of an athlete’s gait cycle, more recent research has suggested that this may constrict the athlete from their “natural” gait cycle. Using an experienced 800m runner this case study aimed to investigate whether the use of a self-selected velocity will increase the reliability and repeatability of seven commonly assessed gait measures. From assessing five trials at both a standardised and self-selected velocity, it was found that only the measures of knee and ankle range of motions and propulsive ground reaction forces were more repeatable with the self-selected velocity. The findings of this study and the locations of these repeatable measures within the gait cycle has lead the author to deduce that the running velocity condition selected for studies must be depend
The analysis of runner’s gait is a common research area with a variety of aims from injury prevention to performance enhancement as well as the evaluation of footwear reflecting the frequent use of running within and outside of the sporting environment (Stacoff et al., 1988; Stacoff et al., 1989; Williams & Ziff, 1991; Nigg et al., 1995; Diss, 2001). One such researched area is the changes in gait mechanics when the velocity at which the athlete runs changes, predominately by increasing the running velocity, and the implication of the mechanical alterations on performance and injury potentials (Arampatzis et al., 1999; Karamanidis et al., 2004). To make testing methodologies within- and between-studies consistent and comparable, the tendency is to place a standardised velocity at which the participants run at (Table 1).
Table 1. Use of standardised running velocities in previous literature
Using the standardised approach, a variety of gait parameters have been found not to only be significantly correlated with running velocity but also between the gait parameters. Both Novacheck (1998) and Kyrolainen et al. (2001) stated that the overall range of motion (RoM) of both the knee and ankle are decreased as running velocity increased through alterations in the knee joint’s total RoM and the ankle joint’s plantar-flexion. The ground reaction force (GRF) components of vertical rate of force production, commonly known as loading rate, and both vertical impact, identified as the braking force, and the propulsive forces have been found to exhibit significant correlations with gait velocity (Riley et al., 2001; Masani et al., 2002; Laughton et al., 2003).
Given the role of the ankle and knee joint in the gait cycle, primarily throughout the stance phase, it is no coincidence that both share such significant correlations with running velocity. The combination of knee flexion and ankle dorsiflexion help in the absorption of the braking forces (Bartlett, 1999; Riley et al., 2001; Ciacci et al., 2010) while the extension of the knee and ankle plantarflexion reaccelerate the movement of the body’s centre of mass (CoM) both horizontally and vertically (Bartlett, 1999; Kyrolainen et al., 2001; Riley et al., 2001). With the increasing velocity, the stance phase of the gait cycle shortens which gives the knee and ankle less time to flex and extend while first absorbing then generating the increasing GRFs. Lelas et al. (2003) identified that it is due to the absorption capabilities of the knee and ankle joint that the increased GRFs are easily attenuated while the rapid extension of the joints and the consequent moment production are the key contributors to the increased propulsive forces (Meinders et al., 1998; Bartlett, 1999).
Queen et al. (2006) introduced the idea of using an individualised participant determined running velocity with the aim to further the work of Ferber et al. (2002) in assessing the repeatability of gait within a single day or between multiple days. The underlying theory is that by placing a standardised running velocity in the methodology there is the potential that this causes alterations to the participant’s natural gait mechanics. While Queen et al. (2006) offered a comparison of the repeatability of the gait parameters within the same day and between multiple days, there was no direct comparison of the variables between the standardised and individualised running velocity conditions. The aim of this case study was to identify if selected parameters were more repeatable in a rear-foot strike runner’s gait when the athlete dictated the running velocity used in testing. It is hypothesised that the use of an athlete’s self-selected velocity will increase the repeatability of the gait mechanics.
Participant Information
An 800m runner with five years competitive experience (22 years old; height = 1.87m; mass = 79.5kg) volunteered for this case study. The participant reported to be a rearfoot strike runner who was injury free and currently in training during the testing. Full informed consent was given from the participant under the guidelines set by the independent ethics board of the University of Roehampton, London. A full briefing was given to the participant to allow them to give their informed consent at a familiarisation session which included a partial replication of the conditions and procedure that the participant will perform during the data collection session. During this familiarisation session, the starting position on the 10m runway was identified so that when the participant conducted the trials, there would be a right foot strike on the middle of the force platform without the athlete “targeting” the platform (Abendroth-Smith, 1996) while running at the desired velocities outlined in the research question. In addition, this session allowed the researchers to calculate the athlete’s self-selected running velocity for the data collection sessions.
Laboratory Set-Up
All data collection, processing and analysis took place inside the biomechanics laboratory, at the University of Roehampton, during a single data collection session. The laboratory was set-up with a nine camera Vicon infra-red automated motion capture system (Model MXF20; Vicon Motion Systems Ltd.; Oxford, UK) with a Kistler force platform (Model 9281C; Kistler Instruments Ltd.; Hampshire, UK) located within the camera system’s calibrated capture volume (Figure 1). The camera system was calibrated prior to the athlete’s arrival to an error rate of <0.1mm at the employed sampling rate of 100Hz with the force platform recording GRFs at a sampling rate of 1000Hz. The force platform was zeroed immediately prior to data collection to minimise the influence on any background noise on the collected data.
Figure 1. Laboratory schematic used for data collection
To gather kinematic data a lower body model was generated through the three-dimensional (3D) tracking of sixteen 10mm diameter retro-reflective markers placed at specified locations on both limbs (Figure 2) and attached using double-sided medical tape. Four markers were used to represent the pelvis, placed on the anterior superior iliac spinae (LASI and RSAI) and the posterior superior iliac spinae (LPSI and RPSI). The upper leg was modelled by additional markers placed on the lateral femoral epicondyles of each knee (LKNE and RKNE) and the lateral thigh (LTHI and RTHI) which were attached on the transvers plane between the limb’s greater trochanter and the knee markers. Similarly, the use of the knee markers and those on the lateral malleolous of both ankles (LANK and RANK) were used in conjunction with markers on the lateral aspect of both shanks (LTIB and RTIB). As the thigh markers the position of the shank markers was on the transverse plane between the lower limb joint markers. Finally, the feet were modelled using the ankle markers and those attached to the heads of the first (LTOE and RTOE) and fifth metatarsals. The final marker was placed on the calcaneous (LHEE and RHEE) at the same height to the toe markers.
Figure 2. Anatomical locations for retro-reflective marker attachments
Variable Definitions
The variables for the case study were selected due to their frequency in previous studies within gait analysis (Novacheck, 1998; Arampatzis et al., 1999; Diss, 2001; Kyrolainen et al., 2001; Riley et al., 2001; Ferber et al., 2002; Karamanidis et al., 2004; Queen et al., 2006) and the high reliability (>0.93) of the variables when analysing a minimum of five trials (Diss, 2001). The variables included both the ankle and knee joint RoM as well as the loading rate, braking and propulsive GRFs with the zero fore-aft shear being the final variable taken into consideration. Knee RoM was defined as the range of flexion and extension that the knee undergoes during the stride that involves the foot striking the force platform. Similarly, the ankle RoM during this stride was identified as the magnitude of movement through plantarflexion and dorsiflexion. For this study of the rear foot strike runner, loading rate was expressed as the time taken for the GRFs to reach the first resultant peak on the GRF trace with this peak classified as the peak braking force. The second peak of the GRF trace was identified as the moment of application of propulsive forces and the magnitude of this peak used as the propulsive force variable. The loading rate, braking and propulsion forces were all normalised by the athlete’s body mass to make the findings comparable with other studies. Zero fore-aft shear was defined as the percentage of the foot-plate contact spent producing negative horizontal forces (Diss, 2001).
Data Collection Procedure
The athlete completed an individualised self-directed warm-up prior to the attachment of the retro-reflective markers which was then followed by the recording of specified anthropometric variables, namely height, mass, leg length, and the widths of both the knee and ankle joints. Height and mass were recorded by a Leicester stadiometer (Seca; Hamburg, Germany) and Seca weighting scales (Seca Model 710; Seca; Hamburg, Germany), respectively, while the leg length was measured between the RSAI and RANK markers using a measuring tape denoting centimetre measurement (Sterling 30cm measuring tape; Fisco Tools Ltd.; Essex, UK). Both knee and ankle joint widths were recorded with bicondylar calliper (Holtain 14cm bicondylar calliper; Holtain Ltd.; Pembrokeshire, UK) measuring between the knee’s medial and lateral femoral epicondyles, and the ankle’s medial and lateral malleoli.
Data collection consisted of 12 successful trials per condition with success characterised by the athlete running at the required velocity with their right foot striking the force platform. With the ±5% variance allowed, for the trial to be successful the running velocity must be between 3.33m/s and 3.68m/s, and between 3.8m/s and 4.2m/s for the standardised and self-selected conditions, respectively. The velocity was determined through the tracking of the RASI marker through the Nexus Vicon software package (Nexus Vicon Version 1.6.1.; Vicon Motion Systems Ltd.; Oxford, UK). From the 12 successful trials collected for each condition, five trials were selected, through a randomised draw by an independent researcher at the university, for analysis.
The marker coordinate data was filtered using a fourth-order Butterworth filter with a 6Hz cut-off frequency in the Nexis Vicon software package prior to its exportation to the modelling software. The 3D model of the lower extremities was created through the Vicon Polygon software package (Vicon Polygon Version 3.5.1.; Vicon Motion Systems Ltd.; Oxford, UK) where the required variable data was extracted for analysis. Six variables were used for the analysis of gait mechanics repeatability with repeatability defined by the magnitude of the variable’s standard deviation with a small magnitude indicating a high level of repeatability.
The participant’s running velocities recorded were only slightly faster and slower than the targeted velocities, for the self-selected and standardised conditions respectively, while showing identical magnitudes of standard deviations for both conditions (Table 2). Larger joint RoM and subsequent variances were recorded when the participant conducted the trials under the standardised velocity conditions with the knee joint recording the higher RoM and larger magnitudes of variance (Table 2). When splitting the ground reaction forces into braking and propulsion phases, the standardised condition showed a reasonably consistent RoM for both the knee and ankle joints, a trend not seen in the self-selected conditions (Figure 3 for the knee joint; Figure 4 for the ankle joint). The knee showed less variation in flexing during the braking phase and a larger variation during its extension through the propulsive phase (Figure 3). The ankle, however, showed a reversal of this trait with less variability during the propulsive phase (Figure 4). As with the total RoM these results are more consistent in the self-selected condition. However, the GRF results showed a reverse trend with the self-selected conditions eliciting larger forces and loading rates, a trend which was echoes in the standard deviations recorded for each variable (Table 2).
Table 2. Comparison of parameter results between the two velocity conditions
Figure 3. Knee range of motion traces for both the standardised velocity condition (left) and the self-selected velocity condition (right)
Figure 4. Ankle range of motion traces for both the standardised velocity condition (left) and the self-selected velocity condition (right)
The aim of this case study was to investigate if an individualised running velocity will increase the repeatability of gait parameters through a reduction of the variance recorded in these parameters. From the analysis of an experienced 800m runner, it was found that where the variance of kinematic variables decreased with a self-selected running velocity, the variance of GRF variables increased when using the individualised running velocity. In accordance with previous studies, both the braking and propulsive were the most repeatable variables, as well as increasing with the use of a faster running velocity (Kyrolainen et al., 2001; Riley et al., 2001; Ferber et al., 2002; Masani et al., 2002; Queen et al., 2006).
Lower limb joints are reported as having differing roles through that gait cycle in the knee prominent in the braking phase and the ankle key for propulsion. Throughout the eccentric phase, within the self-selected condition, the greater consistency in the knee’s flexion indicates its prominent role in CoM velocity arresting in a more controlled manner than the standardised condition. The efficiency of the knee allows the ankle the freedom to vary in preparation for producing propulsive forces whereas in the standardised condition, the ankle is used in a bracing role to control the transition to amortization point. Both the ankle plantarflexion and produced propulsive force are more consistent in the self-selected condition reinforcing that there is a better control of movement production from the extensor muscle activity when using a running velocity that is more commonly used by the athlete (Wank et al., 1998; Kyrolainen et al., 2001).
In accordance with Novacheck (1998) and Kyrolainen et al. (2001) and in opposition to Arampatzis et al. (1999), the knee and ankle RoM decreases with running velocity and become more consistent with the increasing running velocity. The decrement of total joint RoM and increased loading rate of vertical impact forces has been attributed to the lessened magnitude of time available during the stance phase (Kyrolainen et al., 2001) while the consistency could indicate the use of a manipulated leg muscle pre-activation pattern, one gained though running experience (Kyrolainen et al., 2001; Karamanidis et al., 2004). Both Kyrolainen et al. (2001) and Karamanidis et al. (2004) highlight the muscular pre-activation pattern control over the muscle stiffness and their force absorption and generation capabilities. The combination of the inverse correlation between muscle stiffness and joint RoM (Arampatzis et al., 1999; Laughton et al., 2003), in addition to the inverse correlations between running velocity and joint RoM would result in an pre-activation pattern that would increase muscle stiffness as running velocity increases. The consistency of the joint RoM and propulsive forces under the self-selected condition highlights that through experience a muscle pre-activation pattern has been developed due to the known capacity of the limb to absorb and generate forces at this running velocity in a successful and efficient manner.
The zero fore-aft shear value was higher than reported in previous literature (Diss, 2001; Ciacci et al., 2010). With reference to the reasoning from Ciacci et al. (2010), the higher values for the zero fore-aft shear can be attributed to the foot strike characteristics and the running technique of the runner. As the participant in this case study was a reported heel strike runner the longer duration spent in the braking phase can be associated with the increased surface area used in initial contact with the ground and the transition to mid-stance which is not seen in fore-foot strike runners. With the increased consistence and efficiency of the athlete’s capability to produce propulsive forces under the self-selected condition allows the braking phase to be extended without compensating performance while allowing for the larger variances in the study’s findings.
In summary, three of the measures used in the case study showed an in increased repeatability with the application of a self-selected running velocity those that are generally reported for performance-based research questions. From the findings of the current case study, the author would suggest that the use of either a standardised or self-selected running velocity should be based on the research question being investigated. For injury-based research questions, a standardised velocity would be suggested where as the use of a self-selected velocity would be recommended for a performance-based question. However, these suggestions are in reflection to the findings of this individual case study as not all running gait analysis will be similar.
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The author would like to thank the fellow members of the research team, Lauren Dennis and George Weeks, for their assistance during the data collection, processing and analysis phases of the study. Additionally, the author expresses gratitude to Dr Ceri Diss of the University of Roehampton for her advice and supervision throughout the duration of the study, as well as the university’s sports science department for access to their laboratory and equipment to collect the relevant data. Finally, a note of thanks is expressed to the participant for volunteering their time to participate in this case study.