Energetics of kayaking

The metabolic cost of paddling at low speeds (v) was measured from oxygen uptake (VO2) and anaerobic glycolysis in an annular pool or calculated from submaximal VO2 measured at higher speeds when the kayaker was assisted in overcoming water resistance. Also calculated were the total drag (D) and the net mechanical efficiency (e). Each of the above variables was determined in male (n = 17) and female (n = 7) kayakers ranging in experience from beginners to elite. The VO2 increased with v to a peak of approximately 3.4 l.min-1 (80%-100% of peak VO2 during running) in men and of approximately 2.8 l.min-1 in women, while at higher speeds the additional energy was accounted for by anaerobic glycolysis. In all subjects the energy cost to paddle a given distance (C) increased according to a power function with increasing v. The C was lower for the elite male paddlers than for the unskilled group, while that for elite women was slightly less than that for the elite men. Also the rates of increase of C appeared to be inversely proportional to the subjects' skill. Total D for elite men increased from approximately 15 to 60 N over a range of speeds from 1 to 2.2 m.s-1 while those of unskilled men and skilled women for the same speed range were 10-20 N greater and slightly less, respectively. The e increased linearly, but at a different rate, with increases in v for the unskilled and the elite kayakers (males and females) being 4.2% and 6%, respectively, at v = 1.2 m.s-1.     

Energetics of kayaking at submaximal and maximal speeds

The energy cost of kayaking per unit distance (C(k), kJ x m(-1)) was assessed in eight middle- to high-class athletes (three males and five females; 45-76 kg body mass; 1.50-1.88 m height; 15-32 years of age) at submaximal and maximal speeds. At submaximal speeds, C(k) was measured by dividing the steady-state oxygen consumption (VO(2), l x s(-1)) by the speed (v, m x s(-1)), assuming an energy equivalent of 20.9 kJ x l O(-1)(2). At maximal speeds, C(k) was calculated from the ratio of the total metabolic energy expenditure (E, kJ) to the distance (d, m). E was assumed to be the sum of three terms, as originally proposed by Wilkie (1980): E = AnS + alphaVO(2max) x t-alphaVO(2max) x tau(1-e(-t x tau(-1))), were alpha is the energy equivalent of O(2) (20.9 kJ x l O(2)(-1)), tau is the time constant with which VO(2max) is attained at the onset of exercise at the muscular level, AnS is the amount of energy derived from anaerobic energy utilization, t is the performance time, and VO(2max) is the net maximal VO(2). Individual VO(2max) was obtained from the VO(2) measured during the last minute of the 1000-m or 2000-m maximal run. The average metabolic power output (E, kW) amounted to 141% and 102% of the individual maximal aerobic power (VO(2max)) from the shortest (250 m) to the longest (2000 m) distance, respectively. The average (SD) power provided by oxidative processes increased with the distance covered [from 0.64 (0.14) kW at 250 m to 1.02 (0.31) kW at 2000 m], whereas that provided by anaerobic sources showed the opposite trend. The net C(k) was a continuous power function of the speed over the entire range of velocities from 2.88 to 4.45 m x s(-1): C(k) = 0.02 x v(2.26) (r = 0.937, n = 32).     

Specificity of velocity in strength training

Twenty-one male volunteers (ages 23-25 years) were tested pre- and post training for maximal knee extension power at five specific speeds (1.05, 2.09, 3.14, 4.19, and 5.24 rad X s-1) with an isokinetic dynamometer. Subjects were assigned randomly to one of three experimental groups; group S, training at 1.05 rad X s-1 (n = 8), group I, training at 3.14 rad X s-1 (n = 8) or group F, training at 5.24 rad X s-1 (n = 5). Subjects trained the knee extensors by performing 10 maximal voluntary efforts in group S, 30 in group I and 50 in group F six times a week for 8 weeks. Though group S showed significant increases in power at all test speeds, the percent increment decreased with test speed from 24.8% at 1.05 rad X s-1 to 8.6% at 5.24 rad X s-1. Group I showed almost similar increment in power (18.5-22.4 at all test speeds except at 2.09 rad X s-1 (15.4%). On the other hand, group F enhanced power only at faster test speeds (23.9% at 4.19 rad X s-1 and 22.8% at 5.24 rad X s-1).     

Predicting metabolic cost of running with and without backpack loads

In the past, a mathematical equation to predict the metabolic cost of standing or walking (Mw) was developed. However, this equation was limited to speeds less than 2.2 m.s-1 and overestimated the metabolic cost of walking or running at higher speeds. The purpose of this study was, therefore, to develop a mathematical model for the metabolic cost of running (Mr), in order to be able to predict the metabolic cost under a wide range of speeds, external loads and grades. Twelve male subjects were tested on a level treadmill under different combinations of speed and external load. Speed varied between 2.2 to 3.2 m.s-1 using 0.2 m.s-1 intervals and external loads between 0-30 kg with 10 kg intervals. Four of the subjects were also tested at 2 and 4% incline while speed and load remained constant (2.4 m.s-1, 20 kg). The model developed is based on Mw and is proportionately linear with external load (L) carried as follows: Mr = Mw-0.5 (1-0.01L)(Mw -15L-850), (watt) The correlation coefficient between predicted and observed values was 0.99 (P less than 0.01) with SER of 7.7%. The accuracy of the model was validated by its ability to predict the metabolic cost of running under different conditions extracted from the literature. A highly significant correlation (r = 0.95, P less than 0.02, SER = 6.5%) was found between our predicted and the reported values. In conclusion, the new equation permits accurate calculation of energy cost of running under a large range of speeds, external loads and inclines.     

Determination and validity of critical velocity as an index of swimming performance in the competitive swimmer.

The purpose of this investigation was to test whether the concept of critical power used in previous studies could be applied to the field of competitive swimming as critical swimming velocity (vcrit). The vcrit, defined as the swimming velocity over a very long period of time without exhaustion, was expressed as the slope of a straight line between swimming distance (dlim) at each speed (with six predetermined speeds) and the duration (tlim). Nine trained college swimmers underwent tests in a swimming flume to measure vcrit at those velocities until the onset of fatigue. A regression analysis of dlim on tlim calculated for each swimmer showed linear relationships (r2 greater than 0.998, P less than 0.01), and the slope coefficient signifying vcrit ranged from 1.062 to 1.262 m.s-1 with a mean of 1.166 (SD 0.052) m.s-1. Maximal oxygen consumption (VO2max), oxygen consumption (VO2) at anaerobic threshold, and the swimming also velocity at the onset of blood lactate accumulation (vOBLA) were also determined during the incremental swimming test. The vcrit showed significant positive correlations with VO2 at anaerobic threshold (r = 0.818, P less than 0.01), vOBLA (r = 0.949, P less than 0.01) and mean velocity of 400 m freestyle (r = 0.864, P less than 0.01). These data suggested that vcrit could be adopted as an index of endurance performance in competitive swimmers.     

Physiological determinants of best performances in human locomotion

In human locomotion, the metabolic power required (E) to cover a given distance d, in the time t is set by the product of the energy cost of the locomotion (C), i.e. the amount of metabolic energy spent to move over one unit of distance, and the speed (v = d t(-1)): E = Cv = Cdt(-1). Since, for any given d, v is a decreasing function of t and C is either constant or increases with v, it necessarily follows that E is larger the smaller the value of t. Thus, for any given distance and subject, the shortest time will be achieved when E is equal to the individual maximal metabolic power (Emax). In turn, Emax is a decreasing function of t: it depends upon the subject's maximal aerobic power (MAP) and on the maximal amount of energy derived from the full utilisation of anaerobic energy stores (AnS). So, if the relationship between C and (v) in the locomotion at stake and the subject's MAP and AnS are known, his best performance time (BPT) over any given distance can be obtained by solving the equality Emax(t) = E(t). This approach has been applied to estimate individual BPTs in running and cycling. In this paper, the above approach will be used to quantify the role of C, MAP, and AnS in determining BPTs for running, track cycling and swimming. This has been achieved by calculating the changes in BPT obtained when each variable, or a combination thereof, is changed by a given percentage. The results show that in all the three types of locomotion, regardless of the speed, the changes in BPT brought about by changes of C alone account for 45-55% of the changes obtained when all three variables (C, MAP and AnS) are changed by the same amount.     

High school and college baseball pitchers response and glove movements to line drives

The timing of glove movements used by baseball pitchers to catch fast approaching balls (i.e., line drives) was examined in two tests to determine the responses and temporal characteristics of glove movements in high school and college baseball pitchers. Balls were projected toward the head of participants at 34.8 m.s-1 (78 mph) on average in an indoor test and at speeds approaching 58.1 m.s-1 (130 mph) in a field test. Pitchers caught over 80% and 15% of the projected balls in the indoor and field tests, respectively. Analyses of glove responses indicated that all pitchers could track the line drives and produce coordinated glove movements, which were initiated 160 ms (+/-47.8), on average, after the ball was launched. College pitchers made initial glove movements sooner than high school pitchers in the field test (p=0.012). In contrast, average glove velocity for pitchers increased from 1.33 (+/-0.61) to 3.45 (+/-0.86) m.s-1 across the tests, but did not differ between experience levels. Glove movement initiation and speed were unrelated, and pitchers utilized visual information throughout the ball's flight to catch balls that approached at speeds exceeding the estimated speeds in competitive situations.     

Interrelationships among various measures of upper body strength assessed by different contraction modes Evidence for a general strength component

Two studies were conducted in 83 college men to determine the degree of generality of individual differences in upper body muscular strength assessed by different testing modes. In study 1 (N = 43), correlations were computed between four measures of upper body strength using the bench press movement, maximal isokinetic (0.09 rad.s-1), maximal fast (0.126 m.s-1) and slow (0.037 m.s-1) hydraulic, and one repetition maximum (1-RM) free weight bench press (BP). Compared to free weight BP, maximal strength during isokinetic and slow hydraulic BP was approximately 29% and approximately 8% larger, and fast hydraulic BP strength was approximately 63% lower (p less than 0.05). Simple linear regression of isokinetic BP on 1-RM BP yielded r = 0.79, error of prediction (SE) = 12%, and generality = 81%. The corresponding averaged values for the regression of slow and fast hydraulic BP on free weight 1-RM BP were r = 0.77, SE = 13.5%, and generality = 84%. In Study 2 (N = 40), testing included maximal isokinetic concentric and eccentric arm flexion and extension at 0.524, 1.570, and 2.094 rad.s-1. The ratio of concentric to eccentric torque at the 3 speeds averaged 0.68 (flexion) and 0.70 (extension), and eccentric torques were 32% and 30% greater than concentric torques (p less than 0.05). The linear regression between concentric vs. eccentric flexion and extension torques at the three velocities yielded an average r = 0.80, SE = 13.7%, and generality = 73%.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ultrasound speed in equine cortical bone: effects of orientation, density, porosity and temperature

Ultrasound speed, as measured by a transmission technique in equine cortical bone, was found to vary markedly with the direction of the ultrasound path through the bone. Using bone samples from the mid-site of the third metacarpus of 20 horses, the ultrasound speed was measured as 4125 m s-1 in the longitudinal direction, 3442 m s-1 in the circumferential or transverse direction, and 3428 m s-1 in the radial direction. These results confirm the anisotropic properties of compact bone. Ultrasound speed had a positive linear relationship when compared with bone specific gravity of cortical bone (r = 0.773, n = 35, p less than 0.0001), and an inverse linear relationship with porosity. Specific gravity has an inverse correlation with porosity (r = 0.857, n = 35, p less than 0.0001). Over the temperature range of 4-42 degrees C, ultrasound speed varied inversely according to temperature with a logarithmic function giving the best fit. These results have important implications for the clinical applications of ultrasound speed in assessing bone quality in racehorses and provide important basic information for the understanding of the passage of ultrasound through cortical bone, which has possible clinical applications in humans.     

Filter-feeding and cruising swimming speeds of basking sharks compared with optimal models: they filter-feed slower than predicted for their size

Movements of six basking sharks (4.0-6.5 m total body length, L(T)) swimming at the surface were tracked and horizontal velocities determined. Sharks were tracked for between 1.8 and 55 min with between 4 and 21 mean speed determinations per shark track. The mean filter-feeding swimming speed was 0.85 m s(-1) (+/-0.05 S.E., n=49 determinations) compared to the non-feeding (cruising) mean speed of 1.08 m s(-1) (+/-0.03 S.E., n=21 determinations). Both absolute (m s(-1)) and specific (L s(-1)) swimming speeds during filter-feeding were significantly lower than when cruise swimming with the mouth closed, indicating basking sharks select speeds approximately 24% lower when engaged in filter-feeding. This reduction in speed during filter-feeding could be a behavioural response to avoid increased drag-induced energy costs associated with feeding at higher speeds. Non-feeding basking sharks (4 m L(T)) cruised at speeds close to, but slightly faster ( approximately 18%) than the optimum speed predicted by the Weihs (1977) [Weihs, D., 1977. Effects of size on the sustained swimming speeds of aquatic organisms. In: Pedley, T.J. (Ed.), Scale Effects in Animal Locomotion. Academic Press, London, pp. 333-338.] optimal cruising speed model. In contrast, filter-feeding basking sharks swam between 29 and 39% slower than the speed predicted by the Weihs and Webb (1983) [Weihs, D., Webb, P.W., 1983. Optimization of locomotion. In: Webb, P.W., Weihs, D. (Eds.), Fish Biomechanics. Praeger, New York, pp. 339-371.] optimal filter-feeding model. This significant under-estimation in observed feeding speed compared to model predictions was most likely accounted for by surface drag effects reducing optimum speeds of tracked sharks, together with inaccurate parameter estimates used in the general model to predict optimal speeds of basking sharks from body size extrapolations.     

High-speed running performance: a new approach to assessment and prediction.

We hypothesized that all-out running speeds for efforts lasting from a few seconds to several minutes could be accurately predicted from two measurements: the maximum respective speeds supported by the anaerobic and aerobic powers of the runner. To evaluate our hypothesis, we recruited seven competitive runners of different event specialties and tested them during treadmill and overground running on level surfaces. The maximum speed supported by anaerobic power was determined from the fastest speed that subjects could attain for a burst of eight steps (approximately 3 s or less). The maximum speed supported by aerobic power, or the velocity at maximal oxygen uptake, was determined from a progressive, discontinuous treadmill test to failure. All-out running speeds for trials of 3-240 s were measured during 10-13 constant-speed treadmill runs to failure and 4 track runs at specified distances. Measured values of the maximum speeds supported by anaerobic and aerobic power, in conjunction with an exponential constant, allowed us to predict the speeds of all-out treadmill trials to within an average of 2.5% (R2 = 0.94; n = 84) and track trials to within 3.4% (R2 = 0.86; n = 28). An algorithm using this exponent and only two of the all-out treadmill runs to predict the remaining treadmill trials was nearly as accurate (average = 3.7%; R2 = 0.93; n = 77). We conclude that our technique 1) provides accurate predictions of high-speed running performance in trained runners and 2) offers a performance assessment alternative to existing tests of anaerobic power and capacity.     

Muscle ATP loss and lactate accumulation at different work intensities in the exercising Thoroughbred horse

The effect of 2 min treadmill exercise, at speeds of 6-12 m.s-1 on an incline of 5 degrees, upon muscle adenine nucleotide loss and lactate accumulation was studied in six Thoroughbred horses. Minimal change occurred in the adenosine triphosphate (ATP) content of the middle gluteal muscle at speeds of 10 m.s-1 or less, but significant loss (up to 47%) had occurred in all horses by 12 m.s-1. The decline in ATP significantly correlated with the accumulation of muscle lactate, beginning shortly after the accumulation of 40 mmol.kg-1 dry muscle lactate. Decline in muscle ATP was mirrored closely by the appearance of ammonia, and to a lesser extent, hypoxanthine and uric acid in plasma. The results suggest that peak accumulation of any of these, or simply the concentration at a specified recovery time, may be used as a measure of ATP loss in the musculature as a whole. This was not so in the case of xanthine, which may also be formed from the degradation of guanidine nucleotides. An In-In plot of plasma ammonia against treadmill speed indicated a break point in accumulation between 8 and 9 m.s-1. The kinetics of ammonia accumulation with speed differed from those of lactate.     

High-speed running performance is largely unaffected by hypoxic reductions in aerobic power.

We tested the importance of aerobic metabolism to human running speed directly by altering inspired oxygen concentrations and comparing the maximal speeds attained at different rates of oxygen uptake. Under both normoxic (20.93% O2) and hypoxic (13.00% O2) conditions, four fit adult men completed 15 all-out sprints lasting from 15 to 180 s as well as progressive, discontinuous treadmill tests to determine maximal oxygen uptake and the metabolic cost of steady-state running. Maximal aerobic power was lower by 30% (1.00 +/- 0.15 vs. 0.77 +/- 0.12 ml O2. kg-1. s-1) and sprinting rates of oxygen uptake by 12-25% under hypoxic vs. normoxic conditions while the metabolic cost of submaximal running was the same. Despite reductions in the aerobic energy available for sprinting under hypoxic conditions, our subjects were able to run just as fast for sprints of up to 60 s and nearly as fast for sprints of up to 120 s. This was possible because rates of anaerobic energy release, estimated from oxygen deficits, increased by as much as 18%, and thus compensated for the reductions in aerobic power. We conclude that maximal metabolic power outputs during sprinting are not limited by rates of anaerobic metabolism and that human speed is largely independent of aerobic power during all-out runs of 60 s or less.     

Functional diversification within and between muscle synergists during locomotion

Locomotion arises from the complex and coordinated function of limb muscles. Yet muscle function is dynamic over the course of a single stride and between strides for animals moving at different speeds or on variable terrain. While it is clear that motor unit recruitment can vary between and within muscles, we know little about how work is distributed within and between muscles under in vivo conditions. Here we show that the lateral gastrocnemius (LG) of helmeted guinea fowl (Numida meleagris) performs considerably more work than its synergist, the medial gastrocnemius (MG) and that the proximal region of the MG (pMG) performs more work than the distal region (dMG). Positive work done by the LG was approximately twice that of the proximal MG when the birds walked at 0.5 ms -1, and four times when running at 2.0 m s-1. This is probably due to different moments at the knee, as well as differences in motor unit recruitment. The dMG performed less work than the pMG because its apparent dynamic stiffness was greater, and because it exhibited a greater recruitment of slow-twitch fibres. The greater compliance of the pMG leads to increased stretch of its fascicles at the onset of force, further enhancing force production. Our results demonstrate the capacity for functional diversity between and within muscle synergists, which increases with changes in gait and speed.     

The effect of submergence on heart rate and oxygen consumption of swimming seals and sea lions

Respiratory, metabolic, and cardiovascular responses to swimming were examined in two species of pinniped, the harbor seal (Phoca vitulina) and the California sea lion (Zalophus californianus). 1. Harbor seals remained submerged for 82-92% of the time at swimming speeds below 1.2 m.s-1. At higher speeds, including simulated speeds above 1.4 m.s-1, the percentage of time spent submerged decreased, and was inversely related to body weight. In contrast, the percentage of time spent submerged did not change with speed for sea lions swimming from 0.5 m.s-1 to 4.0 m.s-1. 2. During swimming, harbor seals showed a distinct breathhold bradycardia and ventilatory tachycardia that were independent of swimming speed. Average heart rate was 137 beats.min-1 when swimming on the water surface and 50 beats.min-1 when submerged. A bimodal pattern of heart rate also occurred in sea lions, but was not as pronounced as in the seals. 3. The weighted average heart rate (WAHR), calculated from measured heart rate and the percentage time spent on the water surface or submerged, increased linearly with swimming speed for both species. The graded increase in heart rate with exercise load is similar to the response observed for terrestrial mammals. 4. The rate of oxygen consumption increased exponentially with swimming speed in both seals and sea lions. The minimum cost of transport calculated from these rates ranged from 2.3 to 3.6 J.m-1.kg-1, and was 2.5-4.0 times the level predicted for similarly-sized salmonids. Despite different modes of propulsion and physiological responses to swimming, these pinnipeds demonstrate similar transport costs.     

Old men running: mechanical work and elastic bounce

It is known that muscular force is reduced in old age. We investigate what are the effects of this phenomenon on the mechanics of running. We hypothesized that the deficit in force would result in a lower push, causing reduced amplitude of the vertical oscillation, with smaller elastic energy storage and increased step frequency. To test this hypothesis, we measured the mechanical energy of the centre of mass of the body during running in old and young subjects. The amplitude of the oscillation is indeed reduced in the old subjects, resulting in an approximately 20% smaller elastic recovery and a greater step frequency (3.7 versus 2.8 Hz, p=1.9x10(-5), at 15-17 km h(-1)). Interestingly, the greater step frequency is due to a lower aerial time, and not to a greater natural frequency of the system, which is similar in old and young subjects (3.6 versus 3.4 Hz, p=0.2). Moreover, we find that in the old subjects, the step frequency is always similar to the natural frequency, even at the highest speeds. This is at variance with young subjects who adopt a step frequency lower than the natural frequency at high speeds, to contain the aerobic energy expenditure. Finally, the external work to maintain the motion of the centre of mass is reduced in the old subjects (0.9 versus 1.2 J kg(-1) m(-1), p=5.1x10(-6)) due to the lower work done against gravity, but the higher step frequency involves a greater internal work to reset the limbs at each step. The net result is that the total work increases with speed more steeply in the old subjects than in young subjects.     

Comparison of mathematically determined blood lactate and heart rate “threshold” points and relationship with performance

The purpose of this study was to investigate the relationship between threshold points for heart rate (Thfc) and blood lactate (Thla) as determined by two objective mathematical models. The models used were the mono-segmental exponential (EXP) model of Hughson et al. and the log-log (LOG) model of Beaver et al. Inter-correlations of these threshold points and correlations with performance were also studied. Seventeen elite runners (mean, SD = 27.5, 6.5 years; 1.73, 0.05 m; 63.8, 7.3 kg; and maximum oxygen consumption of 67.8, 3.7 ml.kg-1.min-1) performed two maximal multistage running field tests on a 183.9-m indoor track with inclined turns. The initial speed of 9 km.h-1 (2.5 m.s-1) was increased by 0.5 km.h-1 (0.14 m.s-1) every lap for the fc test and by 1 km.h-1 (0.28 m.s-1) every 4 min for the la test. After fitting the la or the fc data to the two mathematical models, the threshold speed was assessed in the LOG model from the intersection of the two linear segments (LOG-la; LOG-fc) and in the EXP model from a tangent point (TI-la; TI-fc). Thla and Thfc speeds computed with the two models were significantly different (P less than 0.001) and poorly correlated (LOG-la vs LOG-fc: r = 0.36, TI-la vs TI-fc: r = 0.13). In general, Thfc were less well correlated with performance than Thla. With two different objective mathematical models, this study has shown significant differences and poor correlations between Thla and Thfc.(ABSTRACT TRUNCATED AT 250 WORDS)     

Incompatibility of endurance- and strength-training modes of exercise

Twenty-two male and female subjects trained for 7 wk for endurance (group E), for strength (group IS), or for both strength and endurance (group C) to evaluate the effect of concurrent performance of both modes of training on the in vivo force-velocity relationship of human muscle and on aerobic power. Endurance training consisted of five 5-min sessions three times a week on cycle ergometer with a work load that approached the subject's peak cycle-ergometer O2 uptake (peak CE VO2). Strength training consisted of two 30-s sets of maximal knee extensions per day performed on an isokinetic dynamometer three times a week at a velocity of 4.19 rad X s-1. Group C performed the same training as groups IS and E, alternating days of strength and endurance training. Subjects (groups C and IS) were tested pre- and posttraining for maximal knee-extension torque at a specific joint angle (0.52 rad below horizontal) for seven specific angular velocities (0, 0.84, 1.68, 2.81, 3.35, 4.19, and 5.03 rad X s-1). Groups C and E were tested for peak CE VO2 pretraining, at 14-day intervals, and posttraining. Group IS showed significant increases in angle-specific maximal torque at velocities up to and including the training speed (4.19 rad X s-1). Group C showed increases (P less than 0.05) at velocities of 0, 0.84, and 1.68 rad X s-1 only. Peak CE VO2, when expressed in relative or absolute terms, increased (P less than 0.05) approximately 18% for both groups E and C.(ABSTRACT TRUNCATED AT 250 WORDS)