John Warmenhoven

Assessment of propulsive pin force and oar angle time-series using functional data analysis in on-water rowing

The graphical presentation of the propulsive force applied at the pin plotted relative to the horizontal angle of the oar has been used practically in on‐water rowing for the qualitative assessment of skill. How the pattern is related to performance variables has not been well identified, particularly for highly trained sculling athletes. Bivariate functional principal components analysis (bfPCA) was used on force‐angle data to identify the main modes of variance in curves representing twenty‐seven female rowers of different competition levels (national level and international level), rowing at 32 strokes per minute in a single scull boat. Discriminant function analysis showed moderate classification of rowers using force‐angle graphs across both sides of the boat, with rate of force development identified as a potentially important characteristic for international rowers. Additionally for the bow‐side, spending less time in the first half of the drive phase was also identified as an important feature for international rowers. Multiple linear regression of scores from the bfPCAs showed that a more pronounced front‐peaked profile was associated with a higher average boat velocity. The results of this demonstrate that different characteristics of the force‐angle graph may be associated with different metrics of performance.

Considerations for the use of functional principal components analysis in sports biomechanics: examples from on-water rowing

Abstract The proliferation of new biomechanical technology in laboratory and field settings facilitates the capture of data-sets consisting of complex time-series. An understanding of the appropriate statistical approaches for analysing and interpreting these data-sets is required and the functional data analysis (FDA) family of statistical techniques has emerged in the biomechanical literature. Given the use of FDA is currently in its infancy with biomechanical data, this paper will form the first of a two part series aiming to address practical issues surrounding the application of FDA techniques in biomechanics. This work focuses on functional principal components analysis (fPCA), which is explored using existing literature and sample data from an on-water rowing database. In particular methodological considerations for the implementation of fPCA such as temporal normalisation of data, removal of unwanted forms of variation in a data-set and documented methods for preserving the original temporal properties within a set of curves are explored in detail as a part of this review. Limitations and strengths of the technique are outlined and recommendations are provided to encourage the appropriate use of fPCA within the field of applied sports biomechanics.

Force coordination strategies in on-water single sculling: Are asymmetries related to better rowing performance?

Asymmetries of the rowing stroke cycle have been assessed with reference to kinematics and foot‐force measures in laboratory testing environments. It remains unclear how asymmetries in propulsive kinetic measures are related to on‐water rowing performance. A new approach for the evaluation of both global and local asymmetries across the entire movement was used to assess the continuous role of asymmetries and whether these change according to the level of competitive representation. Twenty‐seven highly skilled female rowers (national and international competition level), rowing at 32 strokes per minute in a single scull boat, were evaluated. A symmetry index (SI) and functional data analysis (FDA) techniques were applied to a continuous difference time‐series, which described fluctuating asymmetry in propulsive pin forces for each rower. Univariate ANOVAs revealed that differences in asymmetries were present as a factor of competition level for the SI and results of FDA. International athletes were more likely to utilize an asymmetry strategy with increased stroke‐side (port‐side) force early in the drive phase and increased bow‐side (starboard) force through the second half of the drive. This was likely the result of international performers customizing their movement strategies relative to known boat mechanical offsets. The first half of the drive phase was also found to be an adaptive part of the rowing stroke cycle, suggesting asymmetries may have a functional role in successful execution of movements during the rowing stroke.

How gender and boat-side affect shape characteristics of force–angle profiles in single sculling: Insights from functional data analysis

OBJECTIVES To examine whether gender or side of the boat influenced shape characteristics of the force-angle profile in on-water single sculling. DESIGN Cross-sectional study design. METHODS Bivariate functional principal components analysis (bfPCA) was applied to force-angle data to identify the main modes of variance in curves of forty highly skilled male and female rowers (national and international level), rowing at 32 strokes per minute in a single scull boat. RESULTS Separate discriminant function analyses for each side of the boat showed strong classification of rowers for gender. Force application close to (or closely around) the perpendicular oar position was demonstrated to be different between genders. A mixed ANOVA exploring gender, boat side and their interaction revealed that bow and stroke side forces were also statistically different from each other independently of gender. A main effect, independent of side of the boat, was also present for gender and no interaction was found between gender and boat side. Bow side forces seemingly acted as a driver of power and peak force production, while stroke side forces may have acted as a mediator of propulsive forces with an additional potential role in steering due to known asymmetrical offsets in boat rigging. CONCLUSIONS Results demonstrate that propulsive force differences according to gender and boat-side are evident and must be acknowledged and accounted for before force-angle graphs are explored relative to performance measures.

Bivariate functional principal components analysis: considerations for use with multivariate movement signatures in sports biomechanics

Abstract Sporting performance is often investigated through graphical observation of key technical variables that are representative of whole movements. The presence of differences between athletes in such variables has led to terms such as movement signatures being used. These signatures can be multivariate (multiple time-series observed concurrently), and also be composed of variables measured relative to different scales. Analytical techniques from areas of statistics such as Functional Data Analysis (FDA) present a practical alternative for analysing multivariate signatures. When applied to concurrent bivariate time-series multivariate functional principal components analysis (referred to as bivariate fPCA or bfPCA in this paper) has demonstrated preliminary application in biomechanical contexts. Despite this, given the infancy of bfPCA in sports biomechanics there are still necessary considerations for its use with non-conventional or complex bivariate structures. This paper focuses on the application of bfPCA to the force-angle graph in on-water rowing, which is a bivariate structure composed of variables with different units. A normalisation approach is proposed to investigate and standardise differences in variability between the two variables. The results of bfPCA applied to the non-normalised data and normalised data are then compared. Considerations and recommendations for the application of bfPCA in this context are also provided.

Vertical stiffness is not related to anterior cruciate ligament elongation in professional rugby union players

Background Novel research surrounding anterior cruciate ligament (ACL) injury is necessary because ACL injury rates have remained unchanged for several decades. An area of ACL risk mitigation which has not been well researched relates to vertical stiffness. The relationship between increased vertical stiffness and increased ground reaction force suggests that vertical stiffness may be related to ACL injury risk. However, given that increased dynamic knee joint stability has been shown to be associated with vertical stiffness, it is possible that modification of vertical stiffness could help to protect against injury. We aimed to determine whether vertical stiffness is related to measures known to load, or which represent loading of, the ACL. Methods This was a cross-sectional observational study of 11 professional Australian rugby players. Knee kinematics and ACL elongation were measured from a 4-dimensional model of a hopping task which simulated the change of direction manoeuvre typically observed when non-contact ACL injury occurs. The model was generated from a CT scan of the participants knee registered frame by frame to fluoroscopy images of the hopping task. Vertical stiffness was calculated from force plate data. Results There was no association found between vertical stiffness and anterior tibial translation (ATT) or ACL elongation (r=−0.05; p=0.89, and r=−0.07; p=0.83, respectively). ATT was related to ACL elongation (r=0.93; p=0.0001). Conclusions Vertical stiffness was not associated with ACL loading in this cohort of elite rugby players but a novel method for measuring ACL elongation in vivo was found to have good construct validity.

A force profile analysis comparison between functional data analysis, statistical parametric mapping and statistical non-parametric mapping in on-water single sculling

OBJECTIVES To examine whether the Functional Data Analysis (FDA), Statistical Parametric Mapping (SPM) and Statistical non-Parametric Mapping (SnPM) hypothesis testing techniques differ in their ability to draw inferences in the context of a single, simple experimental design. DESIGN The sample data used is cross-sectional (two-sample gender comparison) and evaluation of differences between statistical techniques used a combination of descriptive and qualitative assessments. METHODS FDA, SPM and SnPM t-tests were applied to sample data of twenty highly skilled male and female rowers, rowing at 32 strokes per minute in a single scull boat. Statistical differences for gender were assessed by applying two t-tests (one for each side of the boat). RESULTS The t-statistic values were identical for all three methods (with the FDA t-statistic presented as an absolute measure). The critical t-statistics (tcrit) were very similar between the techniques, with SPM tcrit providing a marginally higher tcrit than the FDA and SnPM tcrit values (which were identical). All techniques were successful in identifying consistent sections of the force waveform, where male and female rowers were shown to differ significantly (p<0.05). CONCLUSIONS This is the first study to show that FDA, SPM and SnPM t-tests provide consistent results when applied to sports biomechanics data. Though the results were similar, selection of one technique over another by applied researchers and practitioners should be based on the underlying parametric assumption of SPM, as well as contextual factors related to the type of waveform data to be analysed and the experimental research question of interest.