Asymmetries in paddle force influence choice of stroke type for canoe slalom athletes.

Canoe slalom is an Olympic discipline where athletes race down a whitewater course in kayaks (K1) or canoes (C1) navigating a set of down-stream and up-stream gates. Kayak paddles are symmetrical and have a blade at each end, whereas C1 paddles have only one blade that must be moved across the boat to perform strokes on either the right or left side. Asymmetries in paddle force between the two sides of the boat may lead to a reduction in predicted race time. The purpose of this study was to quantify asymmetries in the paddle forces between the two sides for slalom paddling. Paddle forces for 42 canoe slalom athletes (C1 and K1) were quantified from the straight sections of a flat-water figure-of-eight course. Paddle forces were measured using strain gauges embedded in the paddle shaft, stroke type was identified using video, and boat trajectory was tracked using inertial measurement units and high-speed GPS: data were fused using in-house analysis software. Paddle forces were quantified by their peak force, and impulse during the stroke. Paddle forces for the kayakers had asymmetries of 14.2 to 17.1% for the male K1M and 11.1 to 14.4% for the women K1W. Canoeists were no more asymmetrical than the kayakers for their 'on-side' strokes between the right and left sides. However, there were considerable differences for their 'off-side' strokes: male C1M off-side paddle forces were similar to their 'on-side' forces for the same side, but the women C1W had a significantly lower (-20.8% to -29.5%) paddle forces for their 'off-side' strokes compared to their 'on-side' strokes on that same side. Despite an increasing number of younger male athletes being introduced to the switching technique, and it being used by C1M athletes in international competitions since 2014, C1M paddlers still do not use switching transitions as much as C1W. The data from this study indicate that there is a biomechanical reason for this sex-based difference in the higher proportion of off-side strokes used by the C1M athletes compared to C1W athletes: and this needs to be considered for optimal technique development and race performance.

Stroke technique in C1 canoe slalom: a simulation study.

Male C1 canoe slalom athletes traditionally used cross transitions to move their paddle to the other side of the boat and off-side strokes to paddle on their non-dominant side. Conversely, female athletes often use a switching transition and on-side strokes on their non-dominant side. The purpose of this study was to use a computer model to assess the relation between cross- or switching techniques, and the relative strength (symmetry) of non-dominant compared to dominant side strokes to race times in C1 canoe slalom. We created a forward dynamics model to predict race times using stroke forces (from an indoor ergometer), drag forces (measured on-water), and probability distributions for stroke and transition times (measured from international canoe slalom competitions). The main effects from an ANOVA (p<0.05) were (i) for a given transition number and strength symmetry the race times were faster when using cross-transitions than switch-transitions (ii) for a given strength symmetry the race times became slower as the number of switch transitions increased, but there was minimal effect of the number of cross-transitions, and (iii) the closer the strength of the strokes were between the dominant and non-dominant side (as symmetry factor approached 100 %), the faster the race times.

EMG Signals Can Reveal Information Sharing between Consecutive Pedal Cycles.

PURPOSE: Producing a steady cadence and power while cycling results in fairly consistent average pedal forces for every revolution, although small fluctuations about an average force do occur. This force can be generated by several combinations of muscles, each with slight fluctuations in excitation for every pedal cycle. Fluctuations such as these are commonly thought of as random variation about average values. However, research into fluctuations of stride length and stride time during walking shows information can be contained in the order of fluctuations. This order, or structure, is thought to reveal underlying motor control strategies. Previously, we found persistent structure in the fluctuations of EMG signals during cycling using entropic half-life analysis. These EMG signals contained fluctuations across multiple timescales, such as those within a burst of excitation, between the burst and quiescent period of a cycle, and across multiple cycles. It was not clear which sources of variation contributed to the persistent structure in the EMG. METHODS: In this study, we manipulated variation at different timescales in EMG intensity signals to identify the sources of structure observed during cycling. Nine participants cycled at a constant power and cadence for 30 min while EMG was collected from six muscles of the leg. RESULTS: We found persistent structure across multiple pedal cycles of average EMG intensities, as well as average pedal forces and durations. In addition, we found the entropic half-life did not quantify fluctuations within a burst of EMG intensity; instead, it detected unstructured variation between the burst and quiescent period within a cycle. CONCLUSIONS: The persistent structure in average EMG intensities suggests that fluctuations in muscle excitation are regulated from cycle to cycle.