The interplay between arms-only propelling efficiency, power output and speed in master swimmers.

PURPOSE: To explore the interplay between arms-only propelling efficiency (η(p)), mechanical power output (W(tot)) and swimming speed (V); these three parameters are indeed related through the following equation V(3) = 1/kη(p)W(tot) (where k is the speed-specific drag; k = F/V(2)); thus, the larger are η(p) and W(tot) the larger is V. We furthermore wanted to test the hypothesis that a multiple linear regression between W(tot), η(p) and V would have a stronger correlation coefficient than a linear regression between W(tot) and V alone. METHODS: To this aim we recruited 29 master swimmers (21 M/8F) who were asked to perform (1) an incremental protocol at the arm-ergometer (dry-land test) to determine W(tot) at VO(2max) (e.g. V(max)); (2) a maximal 200 m swim trial (with a pull buoy: arms only) during which V and η(p) were determined. RESULTS: No relationship was found between W(max) and η(p) (not necessarily the swimmers with the largest W(max) are those with the largest η(p) and vice versa) whereas significant correlations were found between W(max) and V (R = 0.419, P = 0.024) and η(p) and V (R = 0.741, P = 0.001); a multiple linear regression indicates that about 75% of the variability of V can be explained by the variability of W(max) and η(p) (R = 0.865, P < 0.001). CONCLUSIONS: These findings indicate that η(p) should be taken into consideration when the relationship between W(max) and V is investigated and that this allows to better explain the inter-subject variability in performance (swimming speed).

The contribution of underwater kicking efficiency in determining "turning performance" in front crawl swimming.

AIM: The aim of this study was to analyze the effects: 1) of maximal velocity (vout max) and acceleration (aout max) attained during the turn; 2) of deceleration (-aglide) and glide efficiency (GE) in the gliding phase after the turn; and 3) of the efficiency (hF) of the dolphin kick in determining the velocity and acceleration in the first 5 and the following 10 m after a turn (v5, v5-15, a5 and a5-15) in a 100 m simulated front crawl race. METHODS: The experiments were conducted on 13 swimmers (7M/5F) and all the above mentioned parameters were derived from underwater kinematical analysis. RESULTS: The 100 m times were smaller the larger v5, v5-15, a5 and a5-15. In turn, v5, v5-15, a5 and a5-15 were significantly related to vout max and aout max as well as to ηF and GE (R>0.57, P<0.05). CONCLUSION: Data reported in this study indicate that in the first 5-15 m after the turn, velocity is essentially sustained by the force generated by the swimmer on the pool wall but also indicate the importance of an efficient dolphin kick (and of a streamlined glide) in determining the values of velocity and acceleration in this phase of the race.

The Locomotory Index in diplegic and hemiplegic children: the effects of age and speed on the energy cost of walking.

BACKGROUND: The energy cost of locomotion (C) is a useful tool for quantifying the level of walking disability in the clinical evaluation of patients with cerebral palsy (CP). In addition to clinical condition, also age and velocity (v) can influence C, a fact that is often overlooked. AIM: To show: i) that C differs in the clinical subtypes of CP (hemiplegia or diplegia) and ii) that C should be measured at comparable speeds in CP patients and controls (of the same age). DESIGN: Controlled study. SETTING: Pediatric Rehabilitation Unit of "E. Medea" Scientific Institute (Conegliano, TV); Exercise Physiology Lab of University of Verona. POPULATION: Forty-three CP children (32 diplegic: Dg; 11 hemiplegic: Hg) and 20 healthy children (Cg) with an age range of 4-14 years. METHODS: C was measured as the ratio of net oxygen uptake to walking speed (at v from 1 to 6 km·h(-1)). The Locomotory index (LI) was calculated as the ratio of C in Dg/Hg and Cg (of the same age) at the same speed. RESULTS: C decreases with increasing speed in all groups but evolves differently in Hg and Dg: in the former C decreases by increasing age, becoming similar to that of Cg at 12-14 years; in the latter C does not change as a function of age being always larger than in Cg. CONCLUSION AND CLINICAL REHABILITATION IMPACT: Our data highlight the reduction in C with increasing speed and suggest a better prognosis of locomotion for Hg compared to Dg.

The determinants of performance in master swimmers: a cross-sectional study on the age-related changes in propelling efficiency, hydrodynamic position and energy cost of front crawl.

The decrease in swimming performance (v (max)) that occurs with age is a not only consequence of the physiological decrease in maximal metabolic power ([Formula: see text]) but can also be expected to depend on an increase in the energy cost of swimming (C) [Formula: see text] In turn, for a given speed and stroke C = W (d) / (η(P)η(o)) where W (d) is hydrodynamic resistance, η(P) is propelling efficiency and η(o) is overall efficiency. The aim of this study was to measure C in 47 male masters (31-85 years old) swimming the front crawl at sub-maximal, aerobic, speeds. During the experiments propelling efficiency and projected frontal area (A (eff), an index of W (d)) were also determined by kinematic analysis. "Elder" masters (60-80 years) swam at a significantly slower pace (0.65 vs. 0.91 m s(-1)), with a lower η(P) (0.23 vs. 0.31) and a larger A (eff) (0.39 vs. 0.23 m(2)) than "younger" masters (30-60 years). No significant differences in C (1.45 kJ m(-1), on the average) were observed as a function of age or speed, but C values were significantly higher than those assessed in young elite swimmers at the very same speeds; the difference increasing with age with a rate of 0.75 % per year. With the due considerations (in this study the observed changes in η(P), A (eff) and C can be either attributed to changes in speed or age) these data confirm the hypothesis that an increase in C contributes to the decrease in swimming performance that occurs with age.

The determinants of performance in master swimmers: an analysis of master world records.

Human performances in sports decline with age in all competitions/disciplines. Since the effects of age are often compounded by disuse, the study of master athletes provides the opportunity to investigate the effects of age per se on the metabolic/biomechanical determinants of performance. For all master age groups, swimming styles and distances, we calculated the metabolic power required to cover the distance (d) in the best performance time as: E' maxR » C d=BTP » C vmax; where C is the energy cost of swimming in young elite swimmers, vmax = d/BTP is the record speed over the distance d, and BTP was obtained form "cross-sectional data" (http://www.fina.org). To establish a record performance, E' maxR must be equal to the maximal available metabolic power (E'maxA). This was calculated assuming a decrease of 1% per year at 40 - 70 years, 2% at 70 - 80 years and 3% at 80 - 90 years (as indicated in the literature) and compared to the E' maxR values, whereas up to about 55 years of age E' maxR » E' maxA; for older subjects E' maxA > E' maxR; the difference increasing linearly by about 0.30% (backstroke), 1.93% (butterfly), 0.92% (front crawl) and 0.37% (breaststroke) per year (average over the 50, 100 and 200 m distances). These data suggest that the energy cost of swimming increases with age. Hence, the decrease in performance in master swimmers is due to both decrease in the metabolic power available (E' maxA) and to an increase in C.

Energetics of swimming: a historical perspective.

The energy cost to swim a unit distance (C(sw)) is given by the ratio E/v where E is the net metabolic power and v is the swimming speed. The contribution of the aerobic and anaerobic energy sources to E in swimming competitions is independent of swimming style, gender or skill and depends essentially upon the duration of the exercise. C(sw) is essentially determined by the hydrodynamic resistance (W(d)): the higher W(d) the higher C(sw); and by the propelling efficiency (η(P)): the higher η(P) the lower C(sw). Hence, all factors influencing W(d) and/or η(P) result in proportional changes in C(sw). Maximal metabolic power E max and C(sw) are the main determinants of swimming performance; an improvement in a subject's best performance time can more easily be obtained by a reduction of C sw) rather than by an (equal) increase in E max (in either of its components, aerobic or anaerobic). These sentences, which constitute a significant contribution to today's knowledge about swimming energetics, are based on the studies that Professor Pietro Enrico di Prampero and his co-workers carried out since the 1970s. This paper is devoted to examine how this body of work helped to improve our understanding of this fascinating mode of locomotion.

Exercise intensity of head-out water-based activities (water fitness).

The aims of this study were: (i) to measure the exercise intensity (EI) of the most common water-based exercises (WE) at different movement frequencies (f1 = 1.8-2.0 Hz; f2 = 2.0-2.2 Hz; f3 = 2.2-2.4 Hz) and at a standardize movement's amplitude; (ii) to measure EI during a combination (MIX) of these WE. Five WE were selected: "running raising the knees high" (S); "jumping moving the legs sideways" (SJ); "jumping moving the legs backward and forward" (FJ); "alternate forward kicks" (FK); "alternate sideways kicks" (SK). Twelve physically active women were asked to perform these WE at the three frequencies, as well as a combination (MIX) of the WE. EI increased significantly (p < 0.01) with increasing frequency; as an average, for all WE: VO2 ranged from 18 to 25 ml kg(-1) min(-1), HR from 102 to 138 bpm, RPE from 9.8 to 14.4 (at f1 and f3, respectively). In terms of % VO2max, EI ranged from 37 to 54% for S, was similar for SJ and FJ (31-43%) and for FK and SK (47-63%) at f1 and f3, respectively. Thus, a given EI can be attained either by changing the type of exercise and/or the frequency of the movement. The combination of exercises did not change (in terms of VO2, HR and RPE) the intensity of each exercise performed separately. These data can be utilized to control, in terms of exercise type and frequency, the intensity of a proposed water-based activity.

Active and passive drag: the role of trunk incline.

The aim of this study was to investigate the role of trunk incline (TI) and projected frontal area (A(eff)) in determining drag during active/passive measurements. Active drag (D(a)) was measured in competitive swimmers at speeds from 0.6 to 1.4 m s(-1); speed specific drag (D(a)/v(2)) was found to decrease as a function of v (P < 0.001) to indicate that the human body becomes more streamlined with increasing speed. Indeed, both A(eff) and TI were found to decrease with v (P < 0.001) whereas C(d) (the drag coefficient) was found to be unaffected by v. These data suggest that speed specific drag depend essentially on A(eff). Additional data indicate that A(eff) is larger during front crawl swimming than during passive towing (0.4 vs. 0.24 m(2)). This suggest that D(a)/v(2) is larger than D(p)/v(2) and, at a given speed, that D(a) is larger than D(p).

The interplay between propelling efficiency, hydrodynamic position and energy cost of front crawl in 8 to 19-year-old swimmers.

The aim of this study was to investigate the interplay between the arm stroke efficiency (an index of propelling efficiency, eta (P)) and the static and dynamic position in water (indexes of hydrodynamic resistance, W (d)) in determining the energy cost of front crawl (C) during a swimmer's growth. These three parameters are indeed related by the following equation: C=W(d)/(eta(P).eta(o)) where eta (o) is the overall efficiency of swimming. The experiments were carried out on 72 swimmers (38 M and 34 F; 8-19 years) who were asked to swim at 1 m s(-1). The static position in water was assessed by measuring the underwater torque (T'); the dynamic position in water by measuring the projected frontal area (A (eff)). The ratio between the average values of the eldest to youngest class of age was 3.84 and 2.27 for T', 2.13 and 1.68 for A (eff), and 1.13 and 1.24 for eta (P) (in M and F, respectively). The increase in T' and in A (eff) was larger than the increase in efficiency suggesting that, in this age range, C should increase, the more so in M than F. Indeed, C increased by 1.58 in male and 1.17 in female swimmers. Based on the values of C and eta (P) (and assuming a constant value of eta (o)) it is possible to estimate that, in this age range, W (d) increases by about 1.97 in male and 1.32 in female swimmers, an increase which is proportional to the observed increase in A (eff).

Bioenergetics of a slalom kayak (k1) competition.

The aim of this study was: i) to compute an energy balance of a slalom kayak competition by measuring the percentage contributions of the aerobic and anaerobic energy sources to total metabolic power (E(tot)); and ii) to compare these data with those obtained, on the same subjects, over a flat-water course covered at maximal speed in a comparable time. Experiments were performed on eight middle- to high-class slalom kayakers (24.8 +/- 8.1 years of age, 1.75 +/- 0.04 m of stature, and 69.8 +/- 4.7 kg of body mass) who completed the slalom race in 85.8 +/- 5.3 s and covered the flat water course in 88.1 +/- 7.7 s. E(tot) was calculated from measures of oxygen consumption and of blood lactate concentration: it was about 30 % larger during the flat water all-out test (1.72 +/- 0.18 kW) than during the slalom race (1.35 +/- 0.12 kW). However, in both cases, about 50 % of E(tot) derives from aerobic and about 50 % from anaerobic energy sources. These data suggest that, besides training for skill acquisition and for improving anaerobic power, some high intensity, cardiovascular conditioning should be inserted in the training programs of the athletes specialised in this sport.

Energy cost of swimming of elite long-distance swimmers.

The aim of this study was: (1) to assess the energy cost of swimming (C(s), kJ km(-1)) in a group of male (n = 5) and female (n = 5) elite swimmers specialised in long-distance competitions; (2) to evaluate the possible effect of a 2-km trial on the absolute value of C(s). C(s) was assessed during three consecutive 400-m trials covered in a 50-m pool at increasing speeds (v1, v2, v3). After these experiments the subjects swam a 2-km trial at the 10-km race speed (v2km) after which the three 400-m trials were repeated at the same speed as before (v5 = v1, v6 = v2, v7 = v3). C(s) was calculated by dividing the net oxygen uptake at steady state VO2ss by the corresponding average speed (v, m s(-1)). VO2ss was estimated by using back extrapolation technique from breath-to-breath VO2 recorded during the first 30 s of recovery after each test. C(s) increased (from 0.69 kJ m(-1) to 1.27 kJ m(-1)) as a function of v (from 1.29 m s(-1) to 1.50 m s(-1)), its values being comparable to those measured in elite short distance swimmers at similar speeds. In both groups of subjects the speed maintained during the 2-km trial (v2km) was on the average only 1.2% faster than of v2 and v6 (P>0.05), whereas C(s) assessed at the end of the 2-km trial (v2km) turned out to be 21 +/- 26% larger than that assessed at v2 and v6 (P<0.05); the average stroke frequency (SF, cycles min(-1)) during the 2-km trial turned to be about 6% (P<0.05) faster than that assessed at v2 and v6. At v5, C(s) turned out to be 19 +/- 9% (P<0.05) and 22 +/- 27% (0.1 < P = 0.05) larger than at v1 in male and female subjects (respectively). SF was significantly faster (P<0.05, in male subjects) and the distance per stroke (Ds = v/SF) significantly shorter (P<0.05) in female subjects at v5 and v6 than at v1 and v2. These data suggest that the increase of C(s) found after the 2-km trial was likely related to a decrease in propelling efficiency, since the latter is related to the distance per stroke.

The influence of drag on human locomotion in water.

Propulsion in water requires a propulsive force to overcome drag. Male subjects were measured for cycle frequency, energy cost and drag (D) as a function of velocity (V), up to maximal V, for fin and front crawl swimming, kayaking and rowing. The locomotion with the largest propulsive arms and longest hulls traveled the greatest distance per cycle (d/c) and reached higher maximal V. D while locomotoring increased as a function of V, with lower levels for kayaking and rowing at lower Vs. For Vs below 1 m/s, pressure D dominated, while friction D dominated up to 3 m/s, after which wave D dominated total D. Sport training reduced the D, increased d/c, and thus lowered C and increased maximal V. Maximal powers and responses to training were similar in all types of locomotion. To minimize C or maximize V, D has to be minimized by tailoring D type (friction, pressure or wave) to the form of locomotion and velocity.

An energy balance of front crawl.

With the aim of computing a complete energy balance of front crawl, the energy cost per unit distance (C = Ev(-1), where E is the metabolic power and v is the speed) and the overall efficiency (eta(o) = W(tot)/C, where W(tot) is the mechanical work per unit distance) were calculated for subjects swimming with and without fins. In aquatic locomotion W(tot) is given by the sum of: (1) W(int), the internal work, which was calculated from video analysis, (2) W(d), the work to overcome hydrodynamic resistance, which was calculated from measures of active drag, and (3) W(k), calculated from measures of Froude efficiency (eta(F)). In turn, eta(F) = W(d)/(W(d) + W(k)) and was calculated by modelling the arm movement as that of a paddle wheel. When swimming at speeds from 1.0 to 1.4 m s(-1), eta(F) is about 0.5, power to overcome water resistance (active body drag x v) and power to give water kinetic energy increase from 50 to 100 W, and internal mechanical power from 10 to 30 W. In the same range of speeds E increases from 600 to 1,200 W and C from 600 to 800 J m(-1). The use of fins decreases total mechanical power and C by the same amount (10-15%) so that eta(o) (overall efficiency) is the same when swimming with or without fins [0.20 (0.03)]. The values of eta(o) are higher than previously reported for the front crawl, essentially because of the larger values of W(tot) calculated in this study. This is so because the contribution of W(int) to W(tot )was taken into account, and because eta(F) was computed by also taking into account the contribution of the legs to forward propulsion.

Energy balance of human locomotion in water.

In this paper a complete energy balance for water locomotion is attempted with the aim of comparing different modes of transport in the aquatic environment (swimming underwater with SCUBA diving equipment, swimming at the surface: leg kicking and front crawl, kayaking and rowing). On the basis of the values of metabolic power (E), of the power needed to overcome water resistance (Wd) and of propelling efficiency (etaP=Wd/Wtot, where Wtot is the total mechanical power) as reported in the literature for each of these forms of locomotion, the energy cost per unit distance (C=E/v, where v is the velocity), the drag (performance) efficiency (etad=Wd/E) and the overall efficiency (etao=Wtot/E=etad/etaP) were calculated. As previously found for human locomotion on land, for a given metabolic power (e.g. 0.5 kW=1.43 l.min(-1) VO2) the decrease in C (from 0.88 kJ.m(-1) in SCUBA diving to 0.22 kJ.m(-1) in rowing) is associated with an increase in the speed of locomotion (from 0.6 m.s(-1) in SCUBA diving to 2.4 m.s(-1) in rowing). At variance with locomotion on land, however, the decrease in C is associated with an increase, rather than a decrease, of the total mechanical work per unit distance (Wtot, kJ.m(-1)). This is made possible by the increase of the overall efficiency of locomotion (etao=Wtot/E=Wtot/C) from the slow speeds (and loads) of swimming to the high speeds (and loads) attainable with hulls and boats (from 0.10 in SCUBA diving to 0.29 in rowing).

Interplay among the changes of muscle strength, cross-sectional area and maximal explosive power: theory and facts.

A model has recently been proposed to predict the changes of mechanical power (W) during a maximal explosive effort (such as a standing high jump off both feet) following an adaptation (e.g. training/de-training). The model is based on the assumption that, all other things being equal (ceteris paribus), the predicted changes in W depend on the measured changes of muscle force (F) or cross-sectional area (CSA) only. It follows that, if the measured changes in W are not equal to those predicted by the model, factors other than a change in F (or CSA) must be responsible for this difference. The model does not allow the determination of factors specifically involved in the adaptation process but it helps in discriminating whether an adaptation has taken place at a local level (when the observed changes in F would be attributed to factors other than the observed changes in CSA, e.g. co-contractions, fibre type modifications...), or at a central level (when the observed changes in W would be attributed to other factors than the observed changes in F, e.g. co-ordination of multiple joints and muscle groups...), or in both regions. In this paper the model has been applied to data reported in the literature on disuse (BR, bed rest), de-conditioning (SF, space flight), strength training (ST) and de-training (DT). The results of these calculations have confirmed previous observations on the determinants of the adaptation process and further suggest: (1) that training for one specific motor task (e.g. ST) could affect the performance of a second task (e.g. a maximal explosive jump) but that, as soon as the trained motor task is terminated (DT), this ability is re-gained; and (2) that neuromuscular impairment in disuse (BR) is closer to de-training than to the de-conditioning brought about by weightlessness (SF).

How fins affect the economy and efficiency of human swimming.

The aim of the present study was to quantify the improvements in the economy and efficiency of surface swimming brought about by the use of fins over a range of speeds (v) that could be sustained aerobically. At comparable speeds, the energy cost (C) when swimming with fins was about 40 % lower than when swimming without them; when compared at the same metabolic power, the decrease in C allowed an increase in v of about 0.2 ms(-1). Fins only slightly decrease the amplitude of the kick (by about 10 %) but cause a large reduction (about 40 %) in the kick frequency. The decrease in kick frequency leads to a parallel decrease of the internal work rate ((int), about 75 % at comparable speeds) and of the power wasted to impart kinetic energy to the water ((k), about 40 %). These two components of total power expenditure were calculated from video analysis ((int)) and from measurements of Froude efficiency ((k)). Froude efficiency (eta(F)) was calculated by computing the speed of the bending waves moving along the body in a caudal direction (as proposed for the undulating movements of slender fish); eta(F) was found to be 0.70 when swimming with fins and 0.61 when swimming without them. No difference in the power to overcome frictional forces ((d)) was observed between the two conditions at comparable speeds. Mechanical efficiency [(tot)/(Cv), where (tot)=(k)+(int)+(d)] was found to be about 10 % larger when swimming with fins, i.e. 0.13+/-0.02 with and 0.11+/-0.02 without fins (average for all subjects at comparable speeds).

The self selected speed of running in recreational long distance runners.

The aim of this study was to test the hypothesis that the self selected speed in running (vss) is dependent upon the same factors that determine maximal speed in endurance events (e. g. the anaerobic threshold). Experiments were carried out on 8 recreational long distance runners (42.1 +/- 8.6 years of age, 70.1 +/- 10.6 kg of body mass, 1.74 +/- 0.06 m of body height) while they were participating in a 14 day relay race. During the "race" the subjects were not requested to perform maximally but only to cover their running turn (1 hour per day) at their preferred pace. The relationships between heart rate (HR), perceived exertion (RPE), blood lactate concentration ([La]b) and speed (v) were determined in each subject, before the race, during an incremental running test. From these relationships the speed corresponding to a 4 mM concentration of lactate in blood (v4mM) was calculated and found to be 14.3 +/- 1.8 km x h(-1) (n = 8). At this speed the RPE and HR values were 13.6 +/- 1.4 and 156.4 +/- 12.8 bpm, respectively. The average values of speed (vss, 13.4 +/- 0.6 km x h(-1)), RPE (13.5 +/- 1.4) and HR (154.4 +/- 7.6 bpm) measured during the race (n = 47) were not significantly different from those measured at the lactate threshold (v4mM, RPE4mM and v4mM). However, vss and the average HR during the race showed significantly lower variances than v4mM and HR4mM suggesting that, besides the need of avoiding lactate accumulation in blood, other factors must be involved in the choice of speed in running.

From bipedalism to bicyclism: evolution in energetics and biomechanics of historic bicycles.

We measured the metabolic cost (C) and mechanical work of riding historic bicycles at different speeds: these bicycles included the Hobby Horse (1820s), the Boneshaker (1860s), the High Wheeler (1870s), the Rover (1880s), the Safety (1890s) and a modern bicycle (1980s) as a mean of comparison. The rolling resistance and air resistance of each vehicle were assessed. The mechanical internal work (W(INT)) was measured from three-dimensional motion analysis of the Hobby Horse and modern bicycle moving on a treadmill at different speeds. The equation obtained from the modern bicycle data was applied to the other vehicles. We found the following results. (i) Apart from the Rover, which was introduced for safety reasons, every newly invented bicycle improved metabolic economy. (ii) The rolling resistance decreased with subsequent designs while the frontal area and, hence, aerodynamic drag was fairly constant (except for the High Wheeler). (iii) The saddle-assisted body weight relief (which was inaugurated by the Hobby Horse) was responsible for most of the reduction in metabolic cost compared with walking or running. Further reductions in C were due to decreases in stride/pedalling frequency and, hence, W(INT) at the same speeds. (iv) The introduction of gear ratios allowed the use of pedalling frequencies that optimize the power/contraction velocity properties of the propulsive muscles. As a consequence, net mechanical efficiency (the ratio between the total mechanical work and C) was almost constant (0.273 +/- 0.015s.d.) for all bicycle designs, despite the increase in cruising speed. In the period from 1820 to 1890, improved design of bicycles increased the metabolically equivalent speed by threefold compared with walking at an average pace of ca. + 0.5 ms(-1) per decade [corrected]. The speed gain was the result of concurrent technological advancements in wheeled, human-powered vehicles and of 'smart' adaptation of the same actuator (the muscle) to different operational conditions.

Effects of different after-loads and knee angles on maximal explosive power of the lower limbs in humans.

Maximal explosive power during two-leg jumps was measured on four sedentary subjects [mean age 43.0 (SD 10.3) years, mean height 1.74 (SD 0.04) m, mean body mass 73.5 (SD 1.3) kg] using a sledge apparatus with which both force and speed could be directly measured. Different after-loads were obtained by positioning the sledge at five different angles (SA, alpha) in respect to the horizontal so that m x g x sin alpha (where m is the sum of body mass and the mass of the sledge seat, g the acceleration due to gravity) decreased (on average) from 78% body mass at 30 degrees to 27% body mass at 10 degrees, thus simulating conditions of low gravity. The subjects were asked to jump maximally, without counter movement, starting from 70 degrees, 90 degrees, 110 degrees, and 140 degrees of knee angle (KA); the protocol being repeated at 10 degrees, 15 degrees, 20 degrees, 25 degrees and 30 degrees SA. The average (W+(mean)) power output during concentric exercise (CE) was found to decrease when the starting KA was increased, but to be unaffected by SA (i.e. by the after-load, the simulated low g). The higher values of W+(mean) were recorded at 90 degrees KA [15.01 (SD 1.46) W x kg(-1), average for all subjects at all SA]. The subjects were also asked to perform counter movement (CMJ) and rebound jumps (RE) at the same SA as for CE. In CMJ and RE maximal power outputs were also found to be unaffected by the SA; W+(mean) amounted to 16.03 (SD 0.28) W x kg(-1) in CMJ and 16.88 (SD 0.36) W x kg(-1) in RE (average for all subjects at all SA). In CE, CMJ and RE, the instantaneous force at the onset of the positive speed phase (F(i)) was found to increase linearly with SA (i.e. with increasing m x g x sin alpha), and the difference between F(i) in CMJ or RE and F(i) in CE (F(i) in CMJ minus F(i) in CE and F(i) in RE minus F(i) in CE) was unaffected by SA. This indicated that both maximal power and the elastic recoil were unaffected by simulated low g ranging from 1.71 m x s(-2) (at 10 degrees SA) to 4.91 m x s(-2) (at 30 degrees SA).

Energy cost of front-crawl swimming at supra-maximal speeds and underwater torque in young swimmers.

The energy cost of front-crawl swimming (Cs, kJ x m(-1)) at maximal voluntary speeds over distances of 50, 100, 200 and 400 m, and the underwater torque (T') were assessed in nine young swimmers (three males and six females; 12-17 years old). Cs was calculated from the ratio of the total metabolic energy (Es, kJ) spent to the distance covered. Es was estimated as the sum of the energy derived from alactic (AnA1), lactic (AnL) and aerobic (Aer) processes. In turn, AnL was obtained from the net increase of lactate concentration after exercise, AnA1 was assumed to amount to 0.393 kJ x kg(-1) of body mass, and Aer was estimated from the maximal aerobic power of the subject. Maximal oxygen consumption was calculated by means of the back-extrapolation technique from the oxygen consumption kinetics recorded during recovery after a 400-m maximal trial. Underwater torque (T' x N x m), defined as the product of the force with which the feet of a subject lying horizontally in water tends to sink times the distance from the feet to the center of volume of the lungs, was determined by means of an underwater balance. Cs (kJ x m(-1)) turned out to be a continuous function of the speed (v, m x s(-1)) in both males (Cs = 0.603 x 10(0.228v), r2 =0.991; n = 12) and females (Cs = 0.360 x 10(0.339r), r2 = 0.919; n = 24). A significant relationship was found between T' and Cs at 1.2 m x s(-1); Cs = 0.042T' + 0.594, r = 0.839, n = 10, P<0.05. On the contrary, no significant relationships were found between Cs and T' at faster speeds (1.4 and 1.6 m x s(-1)). This suggests that T' is a determinant of Cs only at speeds comparable to that maintained by the subjects over the longest, 400-m distance [mean (SD) 1.20 (0.07) m x s(-1)].