Lars Johansen

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.

Osmoregulatory control of renal sodium excretion after sodium loading in humans

The hypothesis that renal sodium handling is controlled by changes in plasma sodium concentration was tested in seated volunteers. A standard salt load (3.08 mmol/kg body wt over 120 min) was administered as 0.9% saline (Isot) or as 5% saline (Hypr) after 4 days of constant sodium intake of 75 (LoNa+) or 300 mmol/day (HiNa+). Hypr increased plasma sodium by ∼4 mmol/l but increased plasma volume and central venous pressure significantly less than Isot irrespective of diet. After LoNa+, Hypr induced a smaller increase in sodium excretion than Isot (48 ± 8 vs. 110 ± 17 μmol/min). However, after HiNa+the corresponding natriureses were identical (135 ± 33 vs. 139 ± 39 μmol/min), despite significant difference between the increases in central venous pressure. Decreases in plasma ANG II concentrations of 23-52% were inversely related to sodium excretion. Mean arterial pressure, plasma oxytocin and atrial natriuretic peptide concentrations, and urinary excretion rates of endothelin-1 and urodilatin remained unchanged. The results indicate that an increase in plasma sodium may contribute to the natriuresis of salt loading when salt intake is high, supporting the hypothesis that osmostimulated natriuresis is dependent on sodium balance in normal seated humans.

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.

Underestimation of plasma volume changes in humans by hematocrit/hemoglobin method

During water immersion in humans, the use of changes in hematocrit (Hct) and hemoglobin concentration (Hb) underestimates the relative changes in plasma volume (PV) as measured directly with Evans blue (EB). It is not known whether the same is the case during posture changes. Therefore, changes in PV were determined with an EB dilution technique in 10 males before, during, and after an acute posture change from seated to 6 degrees head-down tilt (HDT). The EB method was improved to take into account changes in transcapillary escape rate of albumin-bound EB. Furthermore, blood was sampled from a central venous catheter. Hct and Hb were simultaneously measured. During HDT, PV determined with EB increased by 9.3 +/- 2.0% but increased only 4.5 +/- 0.9% when calculated with the Hct/Hb method (P < 0.05 vs. EB measurements). Thus use of the Hct/Hb method in humans leads to underestimation of the change in PV by as much as 50% during an acute change in posture. Therefore, a direct tracer-dilution method must be used for accurate estimations of changes in PV during changes in posture or other antiorthostatic maneuvers.During water immersion in humans, the use of changes in hematocrit (Hct) and hemoglobin concentration (Hb) underestimates the relative changes in plasma volume (PV) as measured directly with Evans blue (EB). It is not known whether the same is the case during posture changes. Therefore, changes in PV were determined with an EB dilution technique in 10 males before, during, and after an acute posture change from seated to 6° head-down tilt (HDT). The EB method was improved to take into account changes in transcapillary escape rate of albumin-bound EB. Furthermore, blood was sampled from a central venous catheter. Hct and Hb were simultaneously measured. During HDT, PV determined with EB increased by 9.3 ± 2.0% but increased only 4.5 ± 0.9% when calculated with the Hct/Hb method ( P < 0.05 vs. EB measurements). Thus use of the Hct/Hb method in humans leads to underestimation of the change in PV by as much as 50% during an acute change in posture. Therefore, a direct tracer-dilution method must be used for accurate estimations of changes in PV during changes in posture or other antiorthostatic maneuvers.

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.

Preventing hemodilution abolishes natriuresis of water immersion in humans

The hypothesis was tested that hemodilution is one of the determinants of the water immersion (WI)-induced natriuresis. Eight males were subjected to 3 h of 1) WI to the midchest (Chest), 2) WI to the neck combined with thigh cuff-induced (80 mmHg) venous stasis (Neck + stasis), and 3) a seated time control (n = 6). Central venous pressure and left atrial diameter increased to the same extent during Chest and Neck + stasis (P < 0.05), whereas renal sodium excretion only increased during Chest from 77 +/- 7 to 225 +/- 13 micromol/min (P < 0.05). During Chest, plasma colloid osmotic pressure (COP) decreased from 27.7 +/- 0.7 to 25.1 +/- 0.7 mmHg (P < 0.05), and plasma volume (PV) increased from 3,263 +/- 129 to 3,581 +/- 159 ml (P < 0.05), whereas these variables remained unchanged during Neck + stasis. Plasma norepinephrine concentration decreased similarly during Chest and Neck + stasis by 45 +/- 7 and 34 +/- 4%, respectively (P < 0.05), whereas plasma renin activity decreased only during Chest (P < 0.05). In conclusion, during WI in humans 1) hemodilution (decrease in COP and increase in PV) is a pivotal stimulus for the natriuresis and 2) central blood volume expansion without hemodilution does not augment renal sodium output.The hypothesis was tested that hemodilution is one of the determinants of the water immersion (WI)-induced natriuresis. Eight males were subjected to 3 h of 1) WI to the midchest (Chest), 2) WI to the neck combined with thigh cuff-induced (80 mmHg) venous stasis (Neck + stasis), and 3) a seated time control ( n = 6). Central venous pressure and left atrial diameter increased to the same extent during Chest and Neck + stasis ( P < 0.05), whereas renal sodium excretion only increased during Chest from 77 ± 7 to 225 ± 13 μmol/min ( P < 0.05). During Chest, plasma colloid osmotic pressure (COP) decreased from 27.7 ± 0.7 to 25.1 ± 0.7 mmHg ( P< 0.05), and plasma volume (PV) increased from 3,263 ± 129 to 3,581 ± 159 ml ( P < 0.05), whereas these variables remained unchanged during Neck + stasis. Plasma norepinephrine concentration decreased similarly during Chest and Neck + stasis by 45 ± 7 and 34 ± 4%, respectively ( P < 0.05), whereas plasma renin activity decreased only during Chest ( P < 0.05). In conclusion, during WI in humans 1) hemodilution (decrease in COP and increase in PV) is a pivotal stimulus for the natriuresis and 2) central blood volume expansion without hemodilution does not augment renal sodium output.

Vasopressin, angiotensin II and renal responses during water immersion in hydrated humans

1 The hypothesis was tested that in hydrated humans the release of arginine vasopressin and angiotensin II is suppressed by water immersion (WI) and that this is a mechanism of the immersion‐induced diuresis and natriuresis. Seven male subjects on controlled sodium (65‐75 mmol per 24 h for 4 days) and water intake were studied. 2 Plasma vasopressin was promptly suppressed by WI, declining from 0·76 ± 0·13 to 0·23 ± 0·08 pg ml−1 (P < 0·05), with a concomitant increase in renal water output (CH2O) from ‐0·4 ± 0·2 to 4·4 ± 0·7 ml min−1 (P < 0·05). Subsequently, CH2O returned to the level of control, whereas plasma vasopressin remained suppressed. Plasma osmolality gradually increased from 285 ± 1 to 289 ± 1 mosmol kg−1 (P < 0·05). WI caused a 9‐fold increase in renal sodium excretion. Plasma angiotensin II decreased from 27·1 ± 5·3 to 4·3 ± 0·7 pg ml−1 (P < 0·05), and the intraindividual correlation coefficients between sodium excretion rates and angiotensin II concentrations varied between 0·73 and 0·96 (P < 0·002). 3 The data demonstrate that plasma vasopressin and angiotensin II concentrations decrease during WI in hydrated humans, concomitantly with initial increases in CH2O and sodium excretion. Therefore, vasopressin could constitute a mediator of CH2O and angiotensin II of the natriuresis of WI. The subsequent return of CH2O to the level of control is, however, also caused by other factors.

Effects of 12 weeks high-intensity & reduced-volume training in elite athletes.

It was investigated if high-intensity interval training (HIT) at the expense of total training volume improves performance, maximal oxygen uptake and swimming economy. 41 elite swimmers were randomly allocated to a control (CON) or HIT group. For 12 weeks both groups trained ∼12 h per week. HIT comprised ∼5 h vs. 1 h and total distance was ∼17 km vs. 35 km per week for HIT and CON, respectively. HIT was performed as 6-10×10-30 s maximal effort interspersed by 2–4 minutes of rest. Performance of 100 m all-out freestyle and 200 m freestyle was similar before and after the intervention in both HIT (60.4±4.0 vs. 60.3±4.0 s; n = 13 and 133.2±6.4 vs. 132.6±7.7 s; n = 14) and CON (60.2±3.7 vs. 60.6±3.8 s; n = 15 and 133.5±7.0 vs. 133.3±7.6 s; n = 15). Maximal oxygen uptake during swimming was similar before and after the intervention in both the HIT (4.0±0.9 vs. 3.8±1.0 l O2×min−1; n = 14) and CON (3.8±0.7 vs. 3.8±0.7 l O2×min−1; n = 11) group. Oxygen uptake determined at fixed submaximal speed was not significantly affected in either group by the intervention. Body fat % tended to increase (P = 0.09) in the HIT group (15.4±1.6% vs. 16.3±1.6%; P = 0.09; n = 16) and increased (P<0.05) in the CON group (13.9±1.5% vs. 14.9±1.5%; n = 17). A distance reduction of 50% and a more than doubled HIT amount for 12 weeks did neither improve nor compromise performance or physiological capacity in elite swimmers.

Cardiovascular health profile of elite female football players compared to untrained controls before and after short-term football training

Abstract This study examined the intermittent exercise performance and cardiovascular health profile in elite female football players in comparison to untrained young women, as well as a subgroup subjected to football training 2x1 h · week−1 for 16 weeks. Twenty-seven Danish national team players (elite trained, ET) and 28 untrained women (UT) underwent dual-energy X-ray absorptiometry-scanning (DXA), comprehensive transthoracic echocardiography, treadmill and Yo-Yo Intermittent Endurance level 2 (IE2) testing. Eight women in UT were also tested after the football training period. Maximal oxygen uptake rate (VO2max), peak ventilation and peak lactate were 40, 18 and 51% higher (P< 0.01) in ET than UT, respectively. Cardiac dimensions and function were greater in ET than UT, with left ventricular diastolic diameter, right ventricular diastolic diameter, tricuspid annular plane systolic excursion (TAPSE) and peak transmitral flow in early diastole divided by peak transmitral flow velocity in late diastole during atrial contraction (E/A-ratio) being 13, 19, 27 and 41%, respectively, greater in ET than UT (P< 0.001 to< 0.05). Yo-Yo IE2 performance was 7-fold higher in ET than UT (1772 ± 508 vs. 234 ± 66 m, P< 0.001), fat mass was 51% lower (P< 0.001) and high density lipoprotein (HDL) cholesterol levels were 20% higher (P< 0.01). Sixteen weeks of football elevated VO2max and Yo-Yo IE2 performance by 16 and 40%, respectively, and lowered fat mass by 6%. Cardiac function was markedly improved by 16 weeks of football training with 26 and 46% increases in TAPSE and E/A ratio, respectively, reaching levels comparable to ET. In summary, elite female football players have a superior cardiovascular health profile and intermittent exercise performance compared to untrained controls, but short-term football training can markedly improve the cardiovascular health status.

Kidney function and fluid homeostasis

Ever since Yuri Gagarin landed in 1961 having performed the first manned space flight, a number of physiological and medical questions related to weightlessness have been investigated. Before the advent of manned space flight it was hypothesized that the absence of gravitational stress would induce a redistribution of body fluid from the legs headward, due to the absence of hydrostatic pressure gradients (for review see Gauer & Henry 1963), which would in turn induce changes in kidney function and fluid homeostasis. Because changes in kidney function and fluid homeostasis are relatively slow processes, space flight is the optimal condition for investigations of the influence of weightlessness on these variables. Since it was already well known that water immersion and bed rest induced increases in renal fluid and electrolyte excretion, these models were used as means of simulating the expected effects of weightlessness. Indeed, observations of puffy faces and thin legs (‘bird legs’’) in the first astronauts combined with an almost immediate loss of body mass (Norsk & Epstein 1991) initially seemed to verify the hypothesis that increases in central blood volume through stimulation of volume receptors in the thorax induced an increased renal output of fluid and electrolytes and thus a loss in body mass.