Differences in swimming smoothness between elite and non-elite swimmers.

The aim of the study was to investigate whether jerk cost (JC) can discriminate between swimming levels. Nine elite and nine non-elite swimmers swam a 50-m front-crawl sprint wearing a 3D accelerometer on their back between the inferior angles of the scapulae. Lap times and JC were calculated from the acceleration signal and compared between groups and between swimmers within a group. The elite swimmers swam significantly faster lap times than the non-elite swimmers (p < 0.001). They did so with significantly lower levels of JC compared to the non-elite swimmers (p = 0.005). Furthermore, a stepwise multiple linear regression showed JC accounted for 32.9% of the variation in lap time of the elite swimmers. These results indicate that it is possible to discriminate elite from non-elite swimmers using JC: elite swimmers swim with lower JCs than non-elite swimmers. Additionally, swimming at higher speed is associated with more accelerations and decelerations in both elite and non-elite swimmers, which is reflected by higher JCs and lower smoothness. In sum, JC provides an index of swimming technique that is easy to use in training practice.

Heart-Rate Recovery After Warm-up in Swimming: A Useful Predictor of Training Heart-Rate Response?

For training to be optimal, daily training load has to be adapted to the momentary status of the individual athlete, which is often difficult to establish. Therefore, the current study investigated the predictive value of heart-rate recovery (HRR) during a standardized warm-up for training load. Training load was quantified by the variation in heart rate during standardized training in competitive swimmers. Eight female and 5 male Dutch national-level swimmers participated in the study. They all performed 3 sessions consisting of a 300-m warm-up test and a 10 × 100-m training protocol. Both protocols were swum in front crawl at individually standardized velocities derived from an incremental step test. Velocity was related to 75% and 85% heart-rate reserve (% HRres) for the warm-up and training, respectively. Relative HRR during the first 60 s after the warm-up (HRRw-up) and differences between the actual and intended heart rate for the warm-up and the training (ΔHRw-up and ΔHRtr) were determined. No significant relationship between HRRw-up and ΔHRtr was found (F1,37 = 2.96, P = .09, R2 = .07, SEE = 4.65). There was considerable daily variation in ΔHRtr at a given swimming velocity (73-93% HRres). ΔHRw-up and ΔHRtr were clearly related (F1,37 = 74.31, P < .001, R2 = .67, SEE = 2.78). HRR after a standardized warm-up does not predict heart rate during a directly subsequent and standardized training session. Instead, heart rate during the warm-up protocol seems a promising alternative for coaches to make daily individual-specific adjustments to training programs.

Swimming obstructed by dead-water.

In nautical literature, 'dead-water' refers to the obstructive effect encountered by ships moving in stratified water due to the ship generating waves on an interface that separates different water masses. To investigate the hypothesis that open water swimming may also be obstructed by an encounter of dead-water, possibly causing drowning, we performed two experiments that assess the impact of stratified water on swimming. In the first experiment, subjects made a single front-crawl stroke while lying on a carriage that was rolling just above the water surface. The gain in kinetic energy, as a result of the stroke, was far less in stratified than in homogeneous water. In the second experiment, four subjects swam a short distance (5 m) in homogeneous and in two different settings of stratified water. At the same stroke frequency, swimming in stratified conditions was slower by 15%, implying a loss in propulsive power by 40%. Although in nature stratification will be less strong, extrapolation of the results suggests that dead-water might indeed obstruct swimming in open water as well. This effect will be most pronounced during fair weather, when stratification of a shallow surface layer is most easily established. Our findings indicate that swimmers' anecdotal evidence on 'water behaving strangely' may have to be taken more seriously than previously thought.