Kurt Jensen

Influence of body mass on maximal oxygen uptake: effect of sample size

Abstract Basal metabolic rate is scaled to body mass to the power of 0.73, and we evaluated whether a similar scaling applies when the O2 transport capacity of the body is challenged during maximal exercise (i.e. at maximal O2 uptake, V˙O2max). The allometric relationship between V˙O2max and body mass (y=a · xb, where y is V˙O2max and x is body mass) was developed for 967 athletes representing 25 different sports, with up to 157 participants in each sport. With an increasing number of observations, the exponent approached 0.73, while for ventilation the exponent was only 0.55. By using the 0.73 exponent for V˙O2max, the highest value [mean (SD)] for the males was obtained for the runners and cyclists [234 (16) ml · kg−0.73 · min−1], and for the females the highest value was found for the runners [189 (14) ml · kg−0.73 · min−1]. For the females, aerobic power was about 80% of the value achieved by the males. Scaling may help both in understanding variation in aerobic power and in defining the physiological limitations of work capacity.

Crank inertial load affects freely chosen pedal rate during cycling

Cyclists seek to maximize performance during competition, and gross efficiency is an important factor affecting performance. Gross efficiency is itself affected by pedal rate. Thus, it is important to understand factors that affect freely chosen pedal rate. Crank inertial load varies greatly during road cycling based on the selected gear ratio. Nevertheless, the possible influence of crank inertial load on freely chosen pedal rate and gross efficiency has never been investigated. This study tested the hypotheses that during cycling with sub-maximal work rates, a considerable increase in crank inertial load would cause (1) freely chosen pedal rate to increase, and as a consequence, (2) gross efficiency to decrease. Furthermore, that it would cause (3) peak crank torque to increase if a constant pedal rate was maintained. Subjects cycled on a treadmill at 150 and 250 W, with low and high crank inertial load, and with preset and freely chosen pedal rate. Freely chosen pedal rate was higher at high compared with low crank inertial load. Notably, the change in crank inertial load affected the freely chosen pedal rate as much as did the 100 W increase in work rate. Along with freely chosen pedal rate being higher, gross efficiency at 250 W was lower during cycling with high compared with low crank inertial load. Peak crank torque was higher during cycling at 90 rpm with high compared with low crank inertial load. Possibly, the subjects increased the pedal rate to compensate for the higher peak crank torque accompanying cycling with high compared with low crank inertial load.

Muscle fiber type distribution and nonlinear Vo2-power output relationship in cycling

PURPOSE We examined whether reported deviations from linearity of the oxygen uptake (.VO(2))-to-power output (W) relationship during intense cycling exercise correlated with the percentage Type II fibers in the exercising muscle. METHODS Twelve trained young men with known fiber type distribution in the vastus lateralis muscle performed step-increment exercise (40 W.3 min(-1)) to exhaustion. RESULTS .VO(2) increased linearly with W up to about 50% .VO(2max) with a regression equation of .VO(2) (mL.min-1) = 661 + 9.73 W and a correlation coefficient (r) of 1.000. Subsequent .VO(2) values were all greater than corresponding linear estimates (P < 0.001 or 0.0001). Peak exercise excess .VO(2) (measured minus estimated .VO(2) assuming linearity) averaged (SD) 434 (192) mL O(2).min-1 or 10.3 (4.7) % .VO(2max). A comprehensive curvilinearity index defined as the sum of measured minus estimated .VO(2) at the four highest completed exercise trials averaged 973 (460) mL O(2).min-1 or 21.5 (9.4) % .VO(2max). Correlations between percentage Type II fibers and either of the two expressions of curvilinearity were nonsignificant. Delta [H+] (arterialized capillary blood) from basal level to peak exercise correlated with the submaximal curvilinearity index (r = 0.59-0.64; P < 0.05) but not with peak excess .VO(2). There was a trend toward a correlation between delta La and curvilinearity index in % .VO(2max)(r = 0.52; P < 0.10) but not with any of the other curvilinearity expressions. The relative ventilatory activity expressed as .V(E)-to-.VO(2) ratio tended to correlate with peak excess .VO(2) (P < 0.10) but not with curvilinearity index. Signals from motion sensors indicate that coactivation of upper-body musculature coincided with deviation from linearity in the .VO(2)-W relationship. CONCLUSION VO2 during step-increment cycling increases linearly with power output up to about 50% .VO(2max)and then curvilinearly. The degree of curvilinearity is not related to muscle fiber type distribution in the vastus lateralis, and only marginally and insignificantly related (P < 0.10) to the relative degree of hyperventilation or to lactate response. Acidosis, on the other hand, correlated significantly with curvilinearity index. The inclusion of isometrically working, upper-body muscular groups during high-intensity cycling may also contribute to the overshoot in oxygen cost.

Economy in track runners and orienteers during path and terrain running

The aims of the present study were to assess running economy in track runners and orienteers and to identify the factors responsible for any differences. The participants were 11 orienteers and 10 track runners of similar age, body mass, maximal oxygen uptake and training background. However, the orienteers included heavy terrain running in their daily training, whereas the track runners ran almost entirely on the roads and tracks. Maximal oxygen uptake and running economy were calculated during horizontal path running and during cross-country running in rough terrain with steep hills, using a telemetric system (K2, Cosmed, Italy). Running economy during path running was 217+/-12 and 212+/-14 ml x kg(-1) x km(-1) (mean +/- s) in the orienteers and the track runners, respectively. Running economy was impaired by 41-52% in heavy terrain (P < 0.05), and was less pronounced in the orienteers than in the track runners (88+/-18 vs 109+/-26 ml x kg(-1) x km(-1); P < 0.05). In conclusion, the better running economy of orienteers when changing from horizontal path to heavy terrain running could be an innate ability, or it could be speculated that specific training may improve running economy, indicating the importance of specific training for orienteers.

Muscle Glycogen Content Modifies SR Ca2 + Release Rate in Elite Endurance Athletes.

PURPOSE The aim of the present study was to investigate the influence of muscle glycogen content on sarcoplasmic reticulum (SR) function and peak power output (Wpeak) in elite endurance athletes. METHODS Fourteen highly trained male triathletes (VO2max = 66.5 ± 1.3 mL O2·kg·min), performed 4 h of glycogen-depleting cycling exercise (HRmean = 73% ± 1% of maximum). During the first 4 h of recovery, athletes received either water (H2O) or carbohydrate (CHO), separating alterations in muscle glycogen content from acute changes affecting SR function and performance. Thereafter, all subjects received CHO-enriched food for the remaining 20-h recovery period. RESULTS Immediately after exercise, muscle glycogen content and SR Ca release rate was reduced to 32% ± 4% (225 ± 28 mmol·kg dw) and 86% ± 2% of initial levels, respectively (P < 0.01). Glycogen markedly recovered after 4 h of recovery with CHO (61% ± 2% of preexercise) and SR Ca release rate returned to preexercise level. However, in the absence of CHO during the first 4 h of recovery, glycogen and SR Ca release rate remained depressed, with the normalization of both parameters at the end of the 24 h of recovery after receiving a CHO-enriched diet. Linear regression demonstrated a significant correlation between SR Ca release rate and muscle glycogen content (P < 0.01, r = 0.30). The 4 h of cycling exercise reduced Wpeak by 5.5%-8.9% at different cadences (P < 0.05), and Wpeak was normalized after 4 h of recovery with CHO, whereas Wpeak remained depressed (P < 0.05) after water provision. Wpeak was fully recovered after 24 h in both the H2O and the CHO group. CONCLUSION In conclusion, the present results suggest that low muscle glycogen depresses muscle SR Ca release rate, which may contribute to fatigue and delayed recovery of Wpeak 4 h postexercise.

A retrospective cohort study of blood hemoglobin levels in blood donors and competitive rowers

To investigate the distribution of blood hemoglobin levels in healthy blood donors and elite athletes, a retrospective cohort study from 2001 to 2005 of candidate blood donors and elite rowers in Denmark was performed. Eighty‐five thousand eight hundred and forty‐six blood donors were identified (36 962 males), and 3.9% of the males had a blood hemoglobin above 10.5 mM, equalling a hematocrit of 51% and, 1.6% of the females had hemoglobin above 9.7 mM, corresponding to a hematocrit above 47%. One thousand four hundred and six rowers (1116 males) were investigated and 10.4% of the males and 8.3% of the females demonstrated values above the recommended limit for athletic competition. Thus, the prevalence of a high hemoglobin value was greater in the rowers, of both gender, than in the candidate blood donors (P<0.0001). The data demonstrate that high hemoglobin levels in blood are seen regularly in normal people and especially in competition athletes.

Exercise as Treatment for Alcohol Dependence: - A Pilot Study -

Abstract Objective The clinical management of alcohol dependence involves evidence-based knowledge on medical treatment, physical training, and psychological management. This pilot study investigates the effect of physical exercise on cardio-respiratory fitness and socio-psychological outcomes. Design: 10 alcohol patients are included to 12 times moderate intensity exercise in groups. Methods: Aerobic power, anxiety, and depression are measured at baseline and post intervention. Observations of the instructor are described. Results: No significant change of aerobic power, but decreased subjective exhaustion. A trend is shown of decreased depression and less concern. Clinical observations showed the testing environment as obstacle and found the communicative role of the instructor crucial. Conclusion: Future research with regard of adherence has to concentrate on the social and contextual aspects of physical activity as treatment.

Transient impairments in single muscle fibre contractile function after prolonged cycling in elite endurance athletes

Prolonged muscle activity impairs whole‐muscle performance and function. However, little is known about the effects of prolonged muscle activity on the contractile function of human single muscle fibres. The purpose of this study was to investigate the effects of prolonged exercise and subsequent recovery on the contractile function of single muscle fibres obtained from elite athletes.

Slide-based ergometer rowing: Effects on force production and neuromuscular activity.

Force production profile and neuromuscular activity during slide‐based and stationary ergometer rowing at standardized submaximal power output were compared in 14 male and 8 female National Team rowers. Surface electromyography (EMG) was obtained in selected thoracic and leg muscles along with synchronous measurement of handle force and rate of force development (RFD). Compared to stationary conditions, slide‐based peak force decreased by 76 (57–95) N (mean 95% CI) in males (P < 0.001) and 20 (8–31) N (P < 0.05) in females. Stroke rate increased (+10.7%) and late‐phase RFD decreased (−20.7%) in males (P < 0.05). Neuromuscular activity in m. vastus lateralis decreased in the initial drive phase from 59% to 51% of EMGmax in males and from 57% to 52% in females (P < 0.01–0.05), while also decreasing in the late recovery phase from 20% to 7% in males and 17% to 7% in females (P < 0.01). Peak force and maximal neuromuscular activity in the shoulder retractors always occurred in the second quartile of the drive phase. In conclusion, peak force and late‐phase RFD (males) decreased and stroke rate increased (males) during slide‐based compared to stationary ergometer rowing, potentially reducing the risk of overuse injury. Neuromuscular activity was more affected in leg muscles than thoracic muscles by slide‐based ergometer rowing.

Jumping and Hopping in Elite and Amateur Orienteering Athletes and Correlations to Sprinting and Running

PURPOSE Jumping and hopping are used to measure lower-body muscle power, stiffness, and stretch-shortening-cycle utilization in sports, with several studies reporting correlations between such measures and sprinting and/or running abilities in athletes. Neither jumping and hopping nor correlations with sprinting and/or running have been examined in orienteering athletes. METHODS The authors investigated squat jump (SJ), countermovement jump (CMJ), standing long jump (SLJ), and hopping performed by 8 elite and 8 amateur male foot-orienteering athletes (29 ± 7 y, 183 ± 5 cm, 73 ± 7 kg) and possible correlations to road, path, and forest running and sprinting performance, as well as running economy, velocity at anaerobic threshold, and peak oxygen uptake (VO(2peak)) from treadmill assessments. RESULTS During SJs and CMJs, elites demonstrated superior relative peak forces, times to peak force, and prestretch augmentation, albeit lower SJ heights and peak powers. Between-groups differences were unclear for CMJ heights, hopping stiffness, and most SLJ parameters. Large pairwise correlations were observed between relative peak and time to peak forces and sprinting velocities; time to peak forces and running velocities; and prestretch augmentation and forest-running velocities. Prestretch augmentation and time to peak forces were moderately correlated to VO(2peak). Correlations between running economy and jumping or hopping were small or trivial. CONCLUSIONS Overall, the elites exhibited superior stretch-shortening-cycle utilization and rapid generation of high relative maximal forces, especially vertically. These functional measures were more closely related to sprinting and/or running abilities, indicating benefits of lower-body training in orienteering.