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 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.

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 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.

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 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.

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 microgravity on maximal power of lower limbs during very short efforts in humans.

The maximal power of the lower limbs was determined in four astronauts (age 37-53 yr) 1) during maximal pushes of approximately 250 ms on force platforms ["maximal explosive power" (MEP)] or 2) during all-out bouts of 6-7 s on an isokinetic cycloergometer [pedal frequency 1 Hz: maximal cycling power (MCP)]. The measurements were done before and immediately after spaceflights of 31-180 days. Before flight, peak and mean values were 3.18 +/- 0.38 and 1.5 +/- 0. 13 (SD) kW for MEP and 1.17 +/- 0.12 and 0.68 +/- 0.08 kW for MCP, respectively. After reentry, MEP was reduced to 67% after 31 days and to 45% after 180 days. MCP decreased less, attaining approximately 75% of preflight level, regardless of the flight duration. The recovery of MCP was essentially complete 2 wk after reentry, whereas that of MEP was slower, a complete recovery occurring after an estimated time close to that spent in flight. In the same subjects, the muscle mass of the lower limbs, as assessed by NMR, decreased by 9-13%, irrespective of flight duration (J. Zange, K. Müller, M. Schuber, H. Wackerhage, U. Hoffmann, R. W. G unther, G. Adam, J. M. Neuerburg, V. E. Sinitsyn, A. O. Bacharev, and O. I. Belichenko. Int. J. Sports Med. 18, Suppl. 4: S308-S309, 1997). The larger fall in maximal power, compared with that in muscle mass, suggests that a fraction of the former (especially relevant for MEP) is due to the effects of weightlessness on the motor unit recruitment pattern.

Energetics of best performances in middle-distance running.

Oxygen consumption (VO2) and blood lactate concentration were determined during constant-speed track running on 16 runners of intermediate level competing in middle distances (0.8-5.0 km). The energy cost of track running per unit distance (Cr) was then obtained from the ratio of steady-state VO2, corrected for lactate production, to speed; it was found to be independent of speed, its overall mean being 3.72 +/- 0.24 J.kg-1 x m-1 (n = 58; 1 ml O2 = 20.9 J). Maximal VO2 (VO2max) was also measured on the same subjects. Theoretical record times were then calculated for each distance and subject and compared with actual seasonal best performances as follows. The maximal metabolic power (Er max) a subject can maintain in running is a known function of VO2max and maximal anaerobic capacity and of the effort duration to exhaustion (te). Er max was then calculated as a function of te from VO2max, assuming a standard value for maximal anaerobic capacity. The metabolic power requirement (Er) necessary to cover a given distance (d) was calculated as a function of performance time (t) from the product Crdt-1 = Er. The time values that solve the equality Er max(te) = Er(t), assumed to yield the theoretical best t, were obtained by an iterative procedure for any given subject and distance and compared with actual records.(ABSTRACT TRUNCATED AT 250 WORDS)

Bioenergetics and biomechanics of front crawl swimming.

"Underwater torque" (T') is one of the main factors determining the energy cost of front crawl swimming per unit distance (Cs). In turn, T' is defined as the product of the force with which the swimmer's feet tend to sink times the distance between the feet and the center of volume of the lungs. The dependency of Cs on T' was further investigated by determining Cs in a group of 10 recreational swimmers (G1: 4 women and 6 men) and in a group of 8 male elite swimmers (G2) after T' was experimentally modified. This was achieved by securing around the swimmers' waist a plastic tube filled, on different occasions, with air, water, or 1 or 2 kg of lead. Thus, T' was either decreased, unchanged, or increased compared with the natural condition (tube filled with water). Cs was determined, for each T' configuration, at 0.7 m/s for G1 and at 1.0 and 1.2 m/s for G2. For T' equal to the natural value, Cs (in kJ.m-1.m body surface area-2) was 0.36 +/- 0.09 and 0.53 +/- 0.13 for G1 in women and men, respectively, and 0.45 +/- 0.05 and 0.53 +/- 0.06 for G2 at 1.0 and 1.2 m/s, respectively. In a given subject at a given speed, Cs and T' were linearly correlated. To compare different subjects and different speeds, the single values of Cs and T' were normalized by dividing them by the corresponding individual averages. These were calculated from all single values (of Cs or T') obtained from that subject at that speed.(ABSTRACT TRUNCATED AT 250 WORDS)

Energetics of best performances in track cycling.

VO2max and best performance times (BPTs) obtained during maximal voluntary trials over 1, 2, 5, and 10 km from a stationary start were assessed in 10 elite cyclists. Steady-state VO2 and peak blood lactate concentration ([La]b) were also determined in the same subjects pedaling on a track at constant submaximal speeds. The energy cost of cycling (Cc, J.m-1) was calculated as the ratio of VO2, corrected for glycolytic energy production and expressed in W, to v (m.s-1). Individual relationships between Cc and v were described by: Cc = Ccrr + k1 v2 where Ccrr is the energy spent against friction and k1 v2 is that spent against drag. Overall energy cost of cycling (Cctot) was obtained, adding to Cc the energy spent to accelerate the total moving mass from a stationary start. Individual theoretical BPTs were then calculated and compared with the actual ones as follows. The maximal metabolic power sustained at a constant level by a given subject (Emax, W) is a known function of the exhaustion time (te). It depends on his VO2max and maximal anaerobic capacity; it was obtained from individual VO2max and [La]b values. The metabolic power (Ec, W) necessary to cover any given distance (d) is a known function of the performance time over d (td); it is given by Ec = Cctot v = Cctot d td. For all subjects and distances, the t values solving the equalities Emax F(te) = Ec F(td) were calculated and assumed to yield theoretical BPTs. Calculations showed a fairly good agreement between actual and calculated BPTs with an average ratio of 1.035 +/- 0.058.

Effects of stride frequency on mechanical power and energy expenditure of walking.

The energetics and mechanics of walking were investigated at different speeds, both at the freely chosen stride frequency (FCSF) and at imposed ones (up to +/- 40% of FCSF). Metabolic energy expenditure was minimized at FCSF for each speed. Motion analysis allowed to calculate: the mechanical internal work rate (Wint), needed to move the segments with respect to the body center of mass (bcm); the external work rate (Wext), necessary to move bcm in the environment; and the total work rate (Wtot), equal to Wint+Wext. Wtot explains the metabolic optimization only at high speeds, while Wext, differently from previously reported, displays minima which better predict FCSF at all speeds (exception made for 1.39 m.s-1). This is probably caused by an overestimation of Wint due to a more ballistic movement of the limbs at low speeds (and low frequencies). The tendency of Wext to increase at high frequencies is due to a persistent minimal vertical excursion of bcm (about 0.02 m, the "locomotory dead space"). While the match between mechanics and energetics (at FCSF and imposed frequencies) occurs to a certain extent, it could be improved by removing the methodological assumptions about the energy transfer between segments and by the possibility to account for the coactivation of antagonist muscles.

Quantitative evaluation of the stretch reflex before and after hydro kinesy therapy in patients affected by spastic paresis.

The aim of this study was the quantitative evaluation of the myotatic reflex in a group of 26 patients affected by stationary spastic paresis (6: hemiparesis; 5: paraparesis; 8: tetraparesis; 7: multiple sclerosis) before and after a treatment of hydro-kinesy therapy. The treatment was carried out in an indoor pool containing warm (32 degrees C) sea water and consisted of active and passive motion exercises, coordination exercises and immersion walking. The measured parameters were: (i) the peak input force (FpH) measured by means of an instrumented hammer with which the patellar tendon was hit; and (ii) the peak value of the corresponding reflex force of the quadriceps femoris (FpQ) measured by means of a load cell connected to the subject's ankle. The peak values of the reflex response (FpQ) were found to increase as a function of the intensity of the imposed stimulus and to reach a plateau between 15 and 30 N of FpH. A Student's t test applied to the paired values of FpQ (as measured at plateau conditions) on both the lower limbs, before and after therapy, showed no significant changes due to the treatment in the four groups of subjects. However, if all subjects were grouped regardless the type of illness: 1) the average reflex response of the affected limb (the one characterized before therapy by the higher FpQ values) was found to decrease following the treatment (75.1+/-26.7 N pre therapy and 69.1+/-29.3 N post therapy, p = 0.07, n = 26); and 2) the effect of the treatment was found to be significantly larger (p = 0.04, n = 26) on the affected limb (delta FpQ = 6.07+/-16.5 N) as respect with the contra lateral one (delta FpQ = -0.16+/-12.1 N).

Blood lactate during leg exercise in microgravity.

Venous blood lactate concentration ([La]b) was measured in five male subjects (age: 30-50 years; BW: 72-84 kg, VO2max:2.2-3.6 l min-1) during cycloergometric exercise in microgravity obtained by parabolic flight maneuvers of approximately 25 s duration. The subject(s) exercised at 30, 60, 90 and 120 W (60 RPM) for at least 7 min at each intensity. Three consecutive parabolas with approximately 3 min interval were performed at each workload. [La]b was determined at rest and immediately after 60, 90 and 120 W exercise. The day after the flight experiments, the subject(s) underwent the same experimental protocol on the ground and the blood samples were taken at the very same time intervals as on the aircraft. [La]b in flight and control didn't show any appreciable difference once the values are plotted as a function of the relative exercise intensities expressed as a percent of the individual VO2max corrected for the moderate hypoxia prevailing inside the aircraft (cabin barometric pressure = 590 mmHg).

Effects of microgravity on muscular explosive power of the lower limbs in humans.

The maximal explosive power of the lower limbs of one astronaut has been measured before launch, and 2, 6 and 11 days after re-entry from 31 days on the MIR Station (EUROMIR '94). The subject, sitting on the carriage-seat of a Multipurpose Ergometer-Dynamometer (MED) constructed ad hoc in our laboratory, pushed maximally with both feet on two force platforms (knees angle 110 degrees). The carriage was free to move backwards on two rails inclined 20 degrees upwards. The force (F) of the lower limbs and the speed of the carriage (v) were recorded and the instantaneous mechanical power (w) was calculated as w = F * v. The average value of the mechanical power (w max) throughout the explosive effort was then obtained. The overall duration of the push was on the average about 0.3 s. It was observed that, at day R+2, mean force, maximal velocity, maximal power (mean and peak), maximal acceleration and overall mechanical work, were all reduced between 60 and 80% of pre-flight values. However, the recovery was remarkably fast, since all these parameters attained about 90% of pre-flight values by day R+11.

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 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).