Original article written by Athanassios Bissas, Josh Walker, Giorgos Paradisis, Brian Hanley, Catherine Tucker, Nils Jongerius, Aaron Thomas, Stéphane Merlino, Pierre-Jean Vazel, Olivier Girard
Background
Elite caliber sprinting provides insight into the highest level of human athletic performance[1,2]. Because of this, investigations into the mechanical factors contributing to elite sprinting performance have become increasingly abundant over the last two decades[1-6]. In addition to kinetic and kinematic determinants of sprinting performance, analysis of between-limb symmetry has recently become in focus, with an interest in the degree to which asymmetry is related to both performance and risk of injury[7-10]. Despite this attention on the mechanics of sprint performance, analysis of elite sprinters in a competition setting is rare, in large part due to logistical challenges associated with collecting this type of data. In “Asymmetry in sprinting: an insight into sub‐10 and sub‐11 s men and women sprinters” Bissas and colleagues[11] were able to overcome many logistical challenges to film and analyze the 2017 IAAF Men’s and Women’s 100 m Finals. This provided unique insight into multiple kinematic variables at maximum velocity during competition in some of the world’s fastest-ever humans. Moreover, the investigators analyzed between-limb asymmetry during the gait cycle and related it to sprint performance. Overall, this data collection and analysis provides new insight into the role of between-limb asymmetry in elite-level sprinting.
What the authors did
The investigators were able to overcome many of the challenges inherent in competition-based data collection due to the well-planned video set-up and method of calibration. The calibrated field of view was from 47.0 to 55.5 m into the sprint, and the video set-up included five cameras (150 frames per second) used to analyze to whole-body motion for two consecutive steps, and four additional cameras (250 frames per second) focused on the lower body. Three-dimensional analysis of the video yielded a total of 33 kinematic variables, which included spatiotemporal variables (e.g., sprinting velocity, step rate, and step length), joint angular data at specific gait cycle events such as touchdown and toe-off, and vertical and horizontal foot velocities. Of particular interest in this investigation was the quantification of symmetry, which was determined via the rectified symmetry angle (SA) score[10,12]. The SA is a dimensionless term whereby perfect symmetry is indicated by a score of 0% and total asymmetry is indicated by a score of 100%.
Symmetry angle = [45°–arctan (XLeft/XRight)/90°] × 100%
where XLeft is the value for the left side and XRight is the value for the right side.
After collecting and digitizing the video, the investigators explored relationships between the various kinematic variables, sex, performance, and SA.
What the authors found
The SA scores were mostly low, and there were no mean SA differences between men and women for any of the stride parameters. However, a high degree of variation existed within both the group of males and females, and as noted by the authors, magnitude of asymmetry was dependent on the parameter being examined. In other words, the SA scores were not necessarily consistent across the variables of interest, or across the different gait cycle events of touchdown and toe-off. For example, there was a large discrepancy in the SA score for the thigh separation angle at touchdown (30.0 ± 26.4%) and the thigh separation angle at toe-off (2.2 ± 1.8%), indicating the parameter- and event-specific dependency of the magnitude of asymmetry. There was also variability within the individual athletes, with some sprinters demonstrating asymmetries for some variables but not others. Perhaps most important, sprint performance was not related to SA score, with only one of the 33 examined variables demonstrating statistical significance to sprinting performance for either the men or women.
Limitations
As with most studies that investigate athletic performance in the context of competition, several limitations were unavoidable. First, because the event of interest was a World Championship Final in the 100 m dash, the sample size was relatively small (eight males and eight females). Additionally, the field of view between 47.0 to 55.5 m constrained the video collection and analysis to only one complete stride cycle (two steps) during a segment of the sprint where the athletes were at (or approaching) top speed. Therefore, as noted by the authors, it was not possible to determine if the inter-limb variability was greater than the intra-limb variability, which has been mentioned as a threshold for establishing meaningful levels of asymmetry when completing this type of analysis[13]. However, in spite of some unavoidable limitations, this study has many strengths. The first of which is the elite population that was analyzed, which included the fastest humans in the world at the time of data collection in 2017, including the men’s world record holders in the 60 m and 100 m. Additionally, the methods of camera set-up and data collection and analysis yielded a windfall of kinematic variables, which provide great insight both for the focus of the study (symmetry analysis) and simply contributing normative data for internationally elite male and female sprinters at ~top speed in a competition environment. For additional information on the data collection and kinematic analysis, the reader is encouraged to download the freely available Men’s and Women’s 100 m Finals Biomechanical Report from the 2017 IAAF World Championships Biomechanics Research Project[14,15].
What does this mean for coaches
Perhaps the most important practical takeaway was stated by the investigators as follows: “Low to moderate asymmetry is a natural phenomenon in elite sprinting and overall sprinters’ performance is generally not related to their asymmetry magnitudes”[11]. For those in the fields of sports performance and sports medicine, this provides some of the first available insight into the amount of asymmetry that exists during a stride cycle at ~maximum velocity in elite sprinters during competition, and how such asymmetry does (or does not) relate to performance.
Reviewer’s comments
Bissas and colleagues[11] successfully navigated the challenges of collecting kinematic data during an elite level competition and provided both important normative data and insightful analysis of asymmetries in some of the fastest humans of all time. In addition to building the body of knowledge regarding maximum velocity sprinting mechanics and the role of asymmetry in elite level performers, these investigators should be commended for providing a blueprint for in situ data collection from elite level sprint competition.
Recommended resources
- Article – Effects of inter-limb asymmetries on physical and sports performance: a systematic review – Chris Bishop and colleagues
- Article – Mechanical determinants of 100-m sprint running performance – JB Morin and colleagues
- Podcast – Athlete asymmetry & impacts on performance and return To play – Chris Bishop