The bouncing mechanism of running against hindering, or with aiding traction forces: a comparison with running on a slope.

PURPOSE: Much like running on a slope, running against/with a horizontal traction force which either hinders/aids the forward motion of the runner creates a shift in the positive and negative muscular work, which in turn modifies the bouncing mechanism of running. The purpose of the study is to (1) investigate the energy changes of the centre of mass and the storage/release of energy throughout the step during running associated with speed and increasing hindering and aiding traction forces; and (2) compare these changes to those observed when running on a slope. METHODS: Ground reaction forces were measured on eight subjects running on an instrumented treadmill against different traction forces at different speeds. RESULTS: As compared to unperturbed running, running against/with a traction force increases/decreases positive external work by ~ 20-70% and decreases/increases negative work by ~ 40-60%, depending on speed and traction force. The external power to maintain forward motion against a traction is contained by increasing the pushing time and step frequency. When running with an aiding force, the external power during the brake is limited by increasing braking time. Furthermore, the aerial time is increased to reduce the power required to reset the limbs each step. CONCLUSION: Our results show that the bouncing mechanism of running against/with a hindering/aiding traction force is equivalent to that of running on a positive/negative slope.

One leg lateral jumps - a new test for team players evaluation.

AIM: We assessed the subject's capacity to accelerate himself laterally in monopodalic support, a crucial ability in several team sports, on 22 athletes, during series of 10 subsequent jumps, between two force platforms at predetermined distance. METHODS: Vertical and horizontal accelerations of the Centre of Mass (CM), contact and flight times were measured by means of force platforms and the Optojump-System®. Individual mean horizontal and vertical powers and their sum (total power) ranged between 7 and 14.5 W/kg. "Push angle", i.e., the angle with the horizontal along which the vectorial sum of all forces is aligned, was calculated from the ratio between vertical and horizontal accelerations: it varied between 38.7 and 49.4 deg and was taken to express the subject technical ability. RESULTS: The horizontal acceleration of CM, indirectly estimated as a function of subject's mass, contact and flight times, was essentially equal to that obtained from force platforms data. Since the vertical displacement can be easily obtained from flight and contact times, this allowed us to assess the Push angle from Optojump data only. CONCLUSIONS: The power developed during a standard vertical jump was rather highly correlated with that developed during the lateral jumps for right (R=0.80, N.=12) and left limb (R=0.72, N.=12), but not with the push angle for right (R=0.31, N.=12) and left limb (R=-0.43, N.=12). Hence standard tests cannot be utilised to assess technical ability. Lateral jumps test allows the coach to evaluate separately maximal muscular power and technical ability of the athlete, thus appropriately directing the training program: the optimum, for a team-sport player being high power and low push-angle, that is: being "powerful" and "efficient".

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.

Cardioventilatory responses during real or imagined walking at low speed.

There is increasing evidence that motor imagery involves at least in part central processes used in motor control. In order to deepen our understanding on the neural mechanisms underlying vegetative responses to real and imagined exercise, we determined cardioventilatory variables during actual or imagined treadmill walking on flat terrain at speeds of 2, 3.5 or 5 km/h, in a group of 14 healthy volunteers. During actual walking, as expected, a comparable intensity-dependent increase was found in ventilation, oxygen consumption, tidal volume and respiratory rate. Imagined walking led to a significant, albeit small (less than 10%), increase in ventilation and oxygen consumption, and to larger increases (up to 40%) in respiratory rate, which was paralleled by a non significant trend towards a decline of tidal volume. These results confirm and extend previous observations showing that motor imagery is accompanied by centrally induced changes in vegetative responses, and provide evidence for a differential control on respiratory rate and tidal volume.

An analysis of the factors limiting maximal oxygen consumption in healthy subjects.

The factors limiting maximal oxygen consumption (VO2max) in humans are analyzed according to a multifactorial model derived from the O2 conductance equation. The alveolar ventilation (VA) and lung O2 transfer (GL) are not considered to be limiting, at least at sea level in healthy subjects, because changes in VA and/or GL are not accompanied by changes in VO2max, due to the shape of the O2 dissociation curve. Thus, the limits to VO2max are shared between O2 transport by the circulation and a peripheral factor, including O2 transfer from capillaries to tissue and mitochondrial O2 utilization. In untrained healthy subjects at sea level, O2 transport by the circulation is responsible for about 70% of the overall limits, the rest depending on the peripheral factors.

Effects of exercise on maximal instantaneous muscular power of humans.

The maximal instantaneous anaerobic power (w), as determined during a high jump off both feet on a force platform, was measured on eight subjects starting from a resting base line; a base line of steady-state cycloergometric exercise requiring 30, 50, and 70% of individual maximum O2 consumption (VO2max); and a base line of maximal and supramaximal exercise (100 and 120% of VO2max). In addition, w was also measured during the VO2 transients from rest to each of the above work loads. Blood lactate concentration ([Lab]) was determined before and 8 min after the end of each priming load. After the onset of any priming load, w decreases with time reaching in 2 min a steady level that is lower the higher the VO2. For the three lowest work rates, the steady w level is unchanged by increasing the duration of the priming exercise up to 30 min. For low work levels, the decrease of w as a function of VO2 is essentially parallel to that of estimated muscle concentration of ATP ([ATP]). For work levels greater than 60% of VO2max involving a substantial accumulation of lactate, the decrease of w becomes smaller than the estimated drop of muscle [ATP]. This finding is tentatively attributed to an increase of either the mechanical equivalent or of the velocity constant of ATP splitting brought about by the lowering of intracellular muscle pH after lactate accumulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of priming exercise on VO2 kinetics and O2 deficit at the onset of stepping and cycling.

Breath-by-breath O2 uptake (VO2) kinetics and increase of blood lactate concentration (delta Lab) were determined at the onset of square-wave stepping (S) or cycling (C) exercise on six male subjects during 1) transition from rest (R) to constant work load, 2) transition from lower to heavier work loads, wherein the baseline VO2 (VO2 s) was randomly chosen between 20 and 65% of the subjects' maximal O2 uptake (VO2 max), and 3) inverse transition from higher to lower work loads and/or to rest. VO2 differences between starting and arriving levels were 20-60% VO2 max. In C, the VO2 on-response became monotonically slower with increasing VO2 s, the half time (t1/2) increasing from approximately 22 s for VO2 s = R to approximately 63 s when VO2 s approximately equal to 50% VO2 max. In S, the fastest VO2 kinetics (t1/2 = 16 s) was attained from VO2 s = 15-30% VO2 max, the t1/2 being approximately 25 s when starting from R or from 50% VO2 max. The slower VO2 kinetics in C were associated with a much larger delta Lab. The VO2 kinetics in recovery were essentially the same in all cases and could be approximated by a double exponential with t1/2 of 21.3 +/- 6 and 93 +/- 45 s for the fast and slow components, respectively. It is concluded that the O2 deficit incurred is the sum of three terms: 1) O2 stores depletion, 2) O2 equivalent of early lactate production, and 3) O2 equivalent of phosphocreatine breakdown.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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)

Physiological profile of world-class high-altitude climbers.

The functional characteristics of six world-class high-altitude mountaineers were assessed 2-12 mo after the last high-altitude climb. Each climber on one or several occasions had reached altitudes of 8,500 m or above without supplementary O2. Static and dynamic lung volumes and right and left echocardiographic measurements were found to be within normal limits of sedentary controls (SC). Muscle fiber distribution was 70% type I, 22% type IIa, and 7% type IIb. Mean muscle fiber cross-sectional area was significantly smaller than that of SC (-15%) and of long-distance runners (LDR, -51%). The number of capillaries per unit cross-sectional area was significantly greater than that of SC (+ 40%). Total mitochondrial volume was not significantly different from that of SC, but its subsarcolemmal component was equal to that of LDR. Average maximal O2 consumption was 60 +/- 6 ml X kg-1 X min-1, which is between the values of SC and LDR. Average maximal anaerobic power was 28 +/- 2.5 W X kg-1, which is equal to that of SC and 40% lower that that of competitive high jumpers. All subjects were characterized by resting hyperventilation both in normoxia and in moderate (inspired O2 partial pressure = 77 Torr) hypoxia resulting in higher oxyhemoglobin saturation levels in hypoxia. The ventilatory response to four tidal volumes of pure O2 was similar to that of SC. It is concluded that elite high-altitude climbers do not have physiological adaptations to high altitude that justify their unique performance.

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)

VO(2) kinetics reveal a central limitation at the onset of subthreshold exercise in heart transplant recipients.

Because the cardiocirculatory response of heart transplant recipients (HTR) to exercise is delayed, we hypothesized that their O(2) uptake (VO(2)) kinetics at the onset of subthreshold exercise are slowed because of an impaired early "cardiodynamic" phase 1, rather than an abnormal subsequent "metabolic" phase 2. Thus we compared the VO(2) kinetics in 10 HTR submitted to six identical 10-min square-wave exercises set at 75% (36 +/- 5 W) of the load at their ventilatory threshold (VT) to those of 10 controls (C) similarly exercising at the same absolute (40 W; C40W group) and relative load (67 +/- 14 W; C67W group). Time-averaged heart rate, breath-by-breath VO(2), and O(2) pulse (O(2)p) data yielded monoexponential time constants of the VO(2) (s) and O(2)p increase. Separating phase 1 and 2 data permitted assessment of the phase 1 duration and phase 2 VO(2) time constant (). The VO(2) time constant was higher in HTR (38.4 +/- 7.5) than in C40W (22.9 +/- 9.6; P < or = 0. 002) or C67W (30.8 +/- 8.2; P < or = 0.05), as was the O(2)p time constant, resulting from a lower phase 1 VO(2) increase (287 +/- 59 vs. 349 +/- 66 ml/min; P < or = 0.05), O(2)p increase (2.8 +/- 0.6 vs. 3.6 +/- 1.0 ml/beat; P < or = 0.0001), and a longer phase 1 duration (36.7 +/- 12.3 vs. 26.8 +/- 6.0 s; P < or = 0.05), whereas the was similar in HTR and C (31.4 +/- 9.6 vs. 29.9 +/- 5.6 s; P = 0.85). Thus the HTR have slower subthreshold VO(2) kinetics due to an abnormal phase 1, suggesting that the heart is unable to increase its output abruptly when exercise begins. We expected a faster in HTR because of their prolonged phase 1 duration. Because this was not the case, their muscular metabolism may also be impaired at the onset of subthreshold exercise.

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.

The concept of lactate threshold. A short review.

The anaerobic threshold (AT) is a widely used tool for investigating aerobic performance characteristics in physiological of pathological conditions. The aim of the present paper is to show that, when the lactate concentration in blood [Lab] is constant in time, regardless of its absolute level, the whole body energy sources for muscular work are entirely aerobic. In fact, [Lab] can remain constant if, and only if, La production is equal to La removal. Since this last is an entirely aerobic process, it can be shown that the net anaerobic energy yield from La production is nil, even if some muscle fibres are indeed producing La at a non trivial rate. These conditions will be defined as "unevenly aerobic" to distinguish them from: (1) the traditional "evenly aerobic" ones, in which the net La production is also zero, but because neither La production nor La removal are significantly increased, and (2) "true anaerobic" conditions wherein La production exceeds La removal and therefore [Lab] increases continuously in time. Comparison of unevenly versus evenly aerobic conditions shows that in the former case the depletion of the glycogen stores is faster in the muscles (or muscle fibres) that are producing La than in those which remove it. Hence the La producing fibres may become crucial in setting the duration (or intensity) of performance. AT, irrespective of its precise mode of assessment, is presumably a measure of the exercise intensity corresponding (or close) to the transition between evenly and unevenly aerobic conditions, thus explaining why AT is a good estimate of the subjects' training status and/or performance capacity.

Energy expenditure during an ultra-endurance cycling race.

BACKGROUND: The energy expenditure of cycling has been investigated in great detail, mainly during trials performed for relatively short periods of time and under well established conditions. The number of investigations performed on long-lasting races, however, is very limited, probably because of practical difficulties. The aim of the present work was an attempt to estimate the energy requirements of 5 amateur cyclists who participated in an ultra-endurance long-lasting road cycling race. METHODS: A generalized equation obtained from literature was applied to calculate the energy expenditure of 26 to 137 short fractions of the competition. RESULTS: The calculated time weighted net metabolic power output ranged from 6.4 W x kg-1 to 10.8 W x kg-1; the corresponding net energy expenditure per unit distance ranging from 73.1 kJ x km-1 to 110.5 kJ x km-1. The total energy expenditure of the competition (rest included) ranged from 44.2 to 186.4 MJ, depending on the total competition duration. For all subjects, the sum total of the overall energy expenditure increased as a power function of cumulated performance time (kJ = 4872 x t0.77). However, the daily energy expenditure decreases with increasing the duration of the competition. CONCLUSIONS: It is concluded that it is possible to estimate the energy expenditure of ultra-endurance cycling performances, provided that the mechanical power output can be described by well defined equations.

Artificial gravity in Space: vestibular tolerance assessed by human centrifuge spinning on Earth.

Artificial gravity created by the astronauts themselves, without any external power supply, by pedalling on coupled counterrotating bicycles along the inner wall of the space module (Twin Bikes System, TBS), was previously suggested (Antonutto et al., 1991) to prevent musculo-skeletal decay and cardiovascular deconditioning during long term space flights. To investigate whether this unusual rotating environment would determine abnormal stimulations of the vestibular system due to Coriolis cross coupled accelerations, thus leading to acute motion sickness (AMS), the conditions of a rotating environment were reproduced in a human centrifuge. A cycloergometer was fixed to the arm of the centrifuge, the rotation speed of which was equal to that yielding 1 g at the feet level in the TBS (i.e. ranging from 19 to 21 RPM). The ergometer position was such that the combination of the horizontal and gravitational acceleration vectors was 1.414 at the inner ear level and was aligned along the head to feet axis. Three subjects, pedalling at 50 W on a cycloergometer during centrifuge's spinning, were asked to move the head following an AMS' provocation protocol. None of them developed any AMS symptoms. This supports the look of the TBS as tool for avoiding musculo-skeletal and cardiovascular deconditioning during long term space flights.

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.

On-Earth evaluation of neurovestibular tolerance to centrifuge simulated artificial gravity in humans.

NASA: In a previous paper we suggested the use of two mechanically coupled counterrotating bicycles to prevent microgravity deconditioning during long term Space missions, the "Twin Bikes System" (Antonutto et al., 1991). The two bicycles, ridden by the astronauts, move along the inner wall of a cylindrically shaped Space module, thus allowing the astronauts to maintain their physical fitness while inducing along their body axis a centrifugal acceleration vector simulating gravity. However, regardless of the means to generate it, artificial gravity may lead to vestibular disturbances induced by the Coriolis cross-coupled angular accelerations of the semicircular canals due to simultaneous rotation about more than one axis (Benson, 1988 a, b; Nicogossin, 1989 b). Indeed, when a subject begins to rotate at a constant angular velocity around a fixed axis, as for example on a Barany chair, the semicircular canal of the vestibular apparatus centered on this axis sends a signal which fades in about 20-30 s. Thus if the subject does not move the head and has no ocular references, after the transient phase he feels still. Violent motional illusions arise, however, every time he tilts the head in pitch or rolls it. In these cases, in fact, the immediate disengagement of the previous "axial" semicircular canal leads to an illusive rotation in a direction opposite to the prevailing one. At the same time the engagement ex novo of another canal sends a signal correctly related to the new rotational situation. It is generally believed that the cross-coupled stimulation of two canals and the resulting sensorial conflict are the major determinants of "acute motion sickness" (AMS) (Young, 1984; Benson, 1988b).^ieng