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Biomedical subjects

Huub M Toussaint

Publications and source records attributed to Huub M Toussaint.

6 recordsLinked to original sources
PubMed2006

Effect of fatigue on stroking characteristics in an arms-only 100-m front-crawl race.

PURPOSE: Race analyses during swimming provide information on the time-dependent values of, among other variables, a swimmer's clean swimming speed (v), stroke rate (SR), and stroke length (SL). The effect of fatigue on changes in v, SR, and SL was investigated. METHODS: Lap-averaged values of v, SR, and SL while swimming 100 m all out with arms only (trial 1) were related to the decline in mechanical power output measured during an all-out 100-m swim on the MAD system (trial 2), with legs immobilized in both trials. RESULTS: Swimming a 100-m front-crawl sprint using arms only led to a significant 24% decrease in lap-averaged mechanical power output (from 200 to 153 W, P < 0.01). This reduction in power-generating capacity led to a 12.4% decrease in v when lap 1 was compared with lap 4 (from 1.69 to 1.48 m x s(-1), P < 0.01). SR declined throughout the race by 10.6% from 0.85 Hz (lap 1) to 0.76 Hz (lap 4, P < 0.05). Analysis revealed that this decrease in SR was linearly related to the decrease in v. The reduction in SR reflected the reduced propulsive force required to overcome the v-dependent, and therefore lower, drag. CONCLUSION: Decreases in swimming speed throughout a 100-m front-crawl race are the result of decreases in the power-producing capacity of the swimmer (fatigue). This fatigue-induced reduction in swimming speed will lead to a reduction in drag. The SR seems to be accommodated to this reduced power output capacity and concomitant diminished propulsion requirements.

Adolescent↗
PubMed2005

Scaling of lifting forces in relation to object size in whole body lifting.

Subjects prepare for a whole body lifting movement by adjusting their posture and scaling their lifting forces to the expected object weight. The expectancy is based on visual and haptic size cues. This study aimed to find out whether lifting force overshoots related to object size cues disappear or persist over a number of repeated lifts. In addition, the influence of the degree of alternation between load sizes, and the influence of knowledge of actual object weights prior to the lifts, were investigated with regard to their effect on force overshoots. Four experiments were performed using a large and a small box, each of 8.4 kg weight, and varying degrees of alternation between boxes. In two of the experiments, subjects were informed about the weight of the objects, while in the other two experiments they were not informed about the weight of the objects. When boxes were lifted 15 times before switching to the other box, rapid diminishing of force scaling errors was observed. However, when boxes were alternated each lift or after three lifts, persisting force scaling overshoots were found in lifting the large box compared to the small one. When participants were given information regarding the actual object weight, force overshoots in the first pair of large and small box lifts were not different from overshoots in experiments where subjects were not informed about the weight of the objects. This shows that, for occupational lifting, risks related to force overshoots in lifting large objects can persist despite experience in lifting the objects and despite the use of labels indicating the weight of the objects.

Adult↗
PubMed2004

The determination of drag in front crawl swimming.

The measurement of drag while swimming (i.e. active drag) is a controversial issue. Therefore, in a group of six elite swimmers two active drag measurement methods were compared to assess whether both measure the same retarding force during swimming. In method 1 push-off forces are measured directly using the system to measure active drag (MAD-system). In method 2 (the velocity perturbation method, VPM) drag is estimated from the difference in swimming speed when subjects swim twice at maximal effort (assuming equal power output and assuming a quadratic drag-speed relationship): once swimming free, and once swimming with a hydrodynamic body attached that created a known additional resistance. The average drag for the VPM tests (53.2 N) was statistically significant and different from the active drag for the MAD-test (66.9 N), paired Student's t-test: 2.484, 12 DF, p=0.029. A post hoc analysis was performed to assess whether the two methods measure a different phenomenon. Based on the drag speed curve obtained with the MAD-system, the VPM-data were re-examined. For diverging drag determinations the assumption of equal power output of the 'free' trial (swimming free) vs. the towing trial (swimming with hydrodynamic buoy) appeared to be violated. The regression of the relative difference in force (MAD vs. VPM) on the relative difference in power (swimming free vs. swimming with hydrodynamic body) was: %Deltadrag=1.898 x %Deltapower -4.498, r2=0.88. This suggests that the major part of the difference in active drag values is due to a non-equal power output in the 'free' relative towing trial during the VPM-test. The simulation of the violation of the equal power output assumption and the calculation of the effect of an other than quadratic drag-speed relationship corroborated the tentative conclusion that both methods measure essentially the same phenomenon and that active drag differences can be explained by a violation of test assumptions.

Adolescent↗
PubMed2002

Effect of a Fast-skin 'body' suit on drag during front crawl swimming.

The effect on drag of a Speedo Fast-skin suit compared to a conventional suit was studied in 13 subjects (6 males, 7 females) swimming at different velocities between 1.0 and 2.0 m.s-1. The active drag force was directly measured during front crawl swimming using a system of underwater push-off pads instrumented with a force transducer (MAD system). For a range of swimming speeds (1.1, 1.3, 1.5 and 1.7 m.s-1), drag values were estimated. On a group level, a statistically non-significant drag reduction effect of 2% was observed for the Fast-skin suit (p = 0.31). Therefore, the 7.5% reduction in drag claimed by the swimwear manufacturer was not corroborated.

Adolescent↗
PubMed2002

"Pumped-up propulsion" during front crawl swimming.

PURPOSE: It is currently held that propulsion in human front crawl swimming is achieved by lift and drag forces predominantly generated by the hands. Calculation of these propulsive forces relies on the quasi-steady assumption that the fluid dynamic behavior of a hand model in a flow channel (constant velocity and orientation) is similar to that of a hand of a real swimmer. However, both experimental and theoretical analyses suggest that this assumption is questionable and that unsteady and rotational propulsion mechanisms play a significant role. Theoretical considerations suggest that arm rotation could lead to a proximodistal pressure gradient, which would induce significant axial flow along the arm toward the hand. METHODS: To gain insight into such mechanisms, we used tufts to study the flow directions around the arm and hand during the front crawl, which consists of a glide, an insweep, and an outsweep phase. In a second experiment, we measured pressure during the stroke at various points along the arm and hand. RESULTS: It was observed that 1) the flow during insweep and part of the outsweep was highly unsteady; 2) the arm movements were largely rotational; 3) a clear axial flow component, not in the direction of the arm movement, was observed during insweep and outsweep; and 4) both the V-shaped "contracting" arrangement of the tufts during the outsweep and pressure recordings point to a pressure gradient along the direction of the arm during the outsweep, as predicted on theoretical grounds. CONCLUSION: Our results demonstrate the reality of the predicted rotational and unsteady effects during front crawl swimming. We hypothesize that the axial flow observed during the outsweep has a propulsion-enhancing effect by increasing the pressure difference over the hand. Further investigation is required to establish more accurately the role of axial flow on propulsion.

Arm↗