Christophe Schnitzler

Arm coordination, power, and swim efficiency in national and regional front crawl swimmers

The effects of skill level on index of arm coordination (IdC), mechanical power output (P(d)), and swim efficiency were studied in front crawlers swimming at different speeds. Seven national and seven regional swimmers performed an arms-only intermittent graded speed test on the MAD-system and in a free condition. The MAD-system measured the drag (D) and P(d). Swimming speed (v), stroke rate (SR), stroke length (SL), stroke index (SI), relative entry, pull, push, and recovery phase durations, and IdC were calculated. Swim efficiency was assessed from SI, the coefficient of variation of calculated hip intra-cyclic velocity variations (IVV), and the efficiency of propulsion generation, i.e., the ratio of v(2) to tangential hand speed squared (u(2)). Both groups increased propulsive continuity (IdC) and hand speed (u) and applied greater P(d) to overcome active drag with speed increases (p<.05). This motor organization adaptation was adequate because SI, IVV, and v(2)/u(2) were unchanged. National swimmers appeared more efficient, with greater propulsive continuity (IdC) and P(d) to reach higher v than regional swimmers (p<.05). The regional swimmers exhibited a higher u and lower SI, IVV, and v(2)/u(2) compared to national swimmers (p<.05), which revealed lower effectiveness to generate propulsion, suggesting that technique is a major determinant of swimming performance.

Hip velocity and arm coordination in front crawl swimming.

The hip intracyclic velocity variability and the index of coordination in front crawl swimming were examined in relation to performance level. 22 swimmers were assigned to either an elite or a recreational swimming group and performed 4 swim trials at different paces relative to their individual maximum velocity. A velocity meter system was set to determine intracyclic velocity variability and video analysis allowed the determination of the index of coordination. Mean intracyclic velocity variability was lower in the elite swimmers than the recreational swimmers (14.39 ± 1.97 vs. 17.80 ± 4.23%, p<0.05), and remained stable with swim pace (i. e., the relative velocity) for the elite group, whereas it increased for the recreational group (p<0.05). The elite swimmers were characterized by a lower mean index of coordination than the recreational swimmers (-9.6 ± 7.1 vs. -6.9 ± 5.0%, p<0.05), but it increased with swim velocity in the elite group and showed only a tendency in the recreational group (p=0.07). These findings suggest that low intracyclic velocity variability and its stability over a range of swimming paces, which result from optimized inter-arm coordination, are characteristic of skilled performance. Thus, the examination of intracyclic velocity variability and index of coordination variability with different swim paces could provide new insight into skilled performance in swimming.

Effect of velocity and added resistance on selected coordination and force parameters in front crawl.

Schnitzler, C, Brazier, T, Button, C, Seifert, L, and Chollet, D. Effect of velocity and added resistance on selected coordination and force parameters in front crawl. J Strength Cond Res 25(10): 2681–2690, 2011—The effect of (a) increasing velocity and (b) added resistance was examined on the stroke (stroke length, stroke rate [SR]), coordination (index of coordination [IdC], propulsive phases), and force (impulse and peaks) parameters of 7 national-level front crawl swimmers (17.14 ± 2.73 years of swimming; 57.67 ± 1.62 seconds in the 100-m freestyle). The additional resistance was provided by a specially designed parachute. Parachute swimming (PA) and free-swimming (F) conditions were compared at 5 velocities per condition. Video footage was used to calculate the stroke and coordination parameters, and sensors allowed the determination of force parameters. The results showed that (a) an increase in velocity (V) led to increases in SR, IdC, propulsive phase duration, and peak propulsive force (p < 0.05), but no significant change in force impulse per cycle, whatever the condition (PA or F); and (b) in PA conditions, significant increases in the IdC, propulsive phase duration, and force impulse and a decrease in SR were recorded at high velocities (p < 0.05). These results indicated that, in the F condition, swimmers adapted to the change in velocity by modifying stroke and coordination rather than force parameters, whereas the PA condition enhanced the continuity of propulsive action and force development. Added resistance, that is, “parachute training,” can be used for specific strength training purposes as long as swimming is performed near maximum velocity.

Wild European apple (Malus sylvestris (L.) Mill.) population dynamics: insight from genetics and ecology in the Rhine Valley. Priorities for a future conservation programme.

The increasing fragmentation of forest habitats and the omnipresence of cultivars potentially threaten the genetic integrity of the European wild apple (Malus sylvestris (L.) Mill). However, the conservation status of this species remains unclear in Europe, other than in Belgium and the Czech Republic, where it has been declared an endangered species. The population density of M. sylvestris is higher in the forests of the upper Rhine Valley (France) than in most European forests, with an unbalanced age-structure, an overrepresentation of adults and a tendency to clump. We characterize here the ecology, age-structure and genetic diversity of wild apple populations in the Rhine Valley. We use these data to highlight links to the history of this species and to propose guidelines for future conservation strategies. In total, 255 individual wild apple trees from six forest stands (five floodplain forests and one forest growing in drier conditions) were analysed in the field, collected and genotyped on the basis of data for 15 microsatellite markers. Genetic analyses showed no escaped cultivars and few hybrids with the cultivated apple. Excluding the hybrids, the genetically “pure” populations displayed high levels of genetic diversity and a weak population structure. Age-structure and ecology studies of wild apple populations identified four categories that were not randomly distributed across the forests, reflecting the history of the Rhine forest over the last century. The Rhine wild apple populations, with their ecological strategies, high genetic diversity, and weak traces of crop-to-wild gene flow associated with the history of these floodplain forests, constitute candidate populations for inclusion in future conservation programmes for European wild apple.

A Simple Field Test to Assess Endurance in Inexperienced Runners

Schnitzler, C, Heck, G, Chatard, JC, and Ernwein, V. A simple field test to assess endurance in inexperienced runners. J Strength Cond Res 24(8): 2026-2031, 2010-The accuracy of a simple field test, the 3-minute, 30-second endurance capacity test (3′30″ ECT), was evaluated in 12 moderately trained athletes. It consisted of 10 3-minute running bouts, separated by 30-second passive recoveries. The first 5 bouts were performed at 75% of maximal aerobic speed (MAS, which was previously determined), and the last 5 were at a self-selected speed. The result of this test is a speed called Vend, expressed in km·h−1 and calculated as the mean speed for the last 5 bouts. The critical velocity (CV) and the individual anaerobic threshold (IAT) were also determined. Another 17 moderately trained athletes then participated in a test-retest procedure to assess the reproducibility of the 3′30″ ECT. The results showed that Vend was correlated with all studied parameters (p < 0.05). Vend and CV did not differ relative to MAS (Vend: 82.8 ± 3.3% of MAS; CV 82.5 ± 3.3% of MAS; p > 0.05). The test-retest procedure indicated a coefficient of variation of 1.99 ± 1.88%. Vend is thus an interesting indicator because (a) it is based on a noninvasive single-visit protocol, (b) its application is in the heavy exercise domain, and (c) it is highly reproducible. The 3′30″ ECT thus seems to be an adequate test to determine endurance capacity in moderately trained subjects.

Relationships between coordination, active drag and propelling efficiency in crawl

This study examines the relationships between the index of coordination (IdC) and active drag (D) assuming that at constant average speed, average drag equals average propulsion. The relationship between IdC and propulsive efficiency (ep) was also investigated at maximal speed. Twenty national swimmers completed two incremental speed tests swimming front crawl with arms only in free condition and using a measurement of active drag system. Each test was composed of eight 25-m bouts from 60% to 100% of maximal intensity whereby each lap was swum at constant speed. Different regression models were tested to analyse IdC-D relationship. Correlation between IdC and ep was calculated. IdC was linked to D by linear regression (IdC=0.246·D-27.06; R(2)=0.88, P<.05); swimmers switched from catch-up to superposition coordination mode at a speed of ∼1.55ms(-1) where average D is ∼110N. No correlation between IdC and ep at maximal speed was found. The intra-individual analysis revealed that coordination plays an important role in scaling propulsive forces with higher speed levels such that these are adapted to aquatic resistance. Inter-individual analysis showed that high IdC did not relate to a high ep suggesting an individual optimization of force and power generation is at play to reach high speeds.

Analysing expertise through data mining: an example based on treading water

Abstract A classification system of treading water based on a conceptual typology was first established and then verified empirically. The typology was established on two concepts: the nature of the forces created within the water and the type of inter-limb coordination used. Thirty-eight participants were videotaped while treading water. Multivariate statistics were used to understand how the different behavioural types related to expertise. Three distinct groups of coordination patterns were adopted during treading water. A support vector machine procedure was used as a confirmatory procedure. The data mining process provides a methodological framework to analyse expertise in sports activities, and in this context suggests that a taxonomy can be established among the numerous coordination solutions that allow humans to create stabilising forces in the water.

Adaptability in Swimming Pattern: How Do Swimmers Modify Propulsive Action as a Function of Speed?

We aimed to examine how participants of different skill level adapt their stroke when asked to swim at different speeds. 20 subjects divided into (a) low-(n = 6), (b) medium-(n = 8), and (c) high-(n = 7) expertise level swam in front crawl at four different swim paces of 60, 70, 85 and 100 % of their maximal speed in a swimming flume. Eight force sensors placed on the dominant hand helped to determine kinetic parameters (force impulse over 5 s I+; arm stroke impulse I+/arm, which are calculated on integral of the force-time curve). Stroke frequency (SF), stroke length (SL), stroke index (SI), Index of coordination (IdC), propulsive phase duration both in percentage of total cycle (PrP%) and absolute duration (PrPs) were determined using four underwater cameras. Results showed that those populations clearly differ in SL and SI, both indicators of swim efficiency. Whatever the skill, increase in swim speed is highly correlated with I+. However, no clear conclusion could be drawn from the magnitude of kinetic (I+, I+/stroke, Faverage, Ppull, Ppush) and coordination (IdC, PrP%, PrPs) parameters, which were similar in magnitude in low- and high-level swimmers. But examination of adaptive strategies showed that if all swimmers increased I+ by increasing their stroke frequency, medium- and high-level swimmers were capable of reorganizing inter- arm movement coordination patterns to increase I+/arm. This study shows how more skilled swimmers adapt their coordination in a subtle way to get attuned with their environment.

To Glide or not to Glide.... Response to Havriluk's Comment on “Arm Coordination and Performance Level in the 400-m Front Crawl”

We recently published an article on arm coordination and performance level in 400-m front-crawl swimming in Research Quarterly for Exercise and Sport (Schnitzler, Seifert, & Chollet, 2011). The index of coordination (IdC) was used to quantify interarm coordination. Our results showed that expert swimmers exhibited lower IdC than recreational swimmers over a 400-m trial. In addition to criticizing various methodological points, Havriluk (2012) challenged our conclusion that catch-up could be an efficient model of coordination and instead suggested that it might lead to injuries. An important point in this debate, however, is that our definition of catch-up coordination may differ from the one proposed by Havriluk (2012), which would explain why we consider catch-up coordination to be the dominant mode of coordination used by expert swimmers during training sessions.