Biomedical subjects

Markus Amann

Publications and source records attributed to Markus Amann.

10 recordsLinked to original sources

PubMed2006

Effect of arterial oxygenation on quadriceps fatigability during isolated muscle exercise.

The effect of various levels of oxygenation on quadriceps muscle fatigability during isolated muscle exercise was assessed in six male subjects. Twitch force (Q(tw)) was assessed using supramaximal magnetic femoral nerve stimulation. In experiment 1, maximal voluntary contraction (MVC) and Q(tw) of resting quadriceps muscle were measured in normoxia [inspired O(2) fraction (Fi(O(2))) = 0.21, percent arterial O(2) saturation (Sp(O(2))) = 98.4%, estimated arterial O(2) content (Ca(O(2))) = 20.8 ml/dl], acute hypoxia (Fi(O(2)) = 0.11, Sp(O(2)) = 74.6%, Ca(O(2)) = 15.7 ml/dl), and acute hyperoxia (Fi(O(2)) = 1.0, Sp(O(2)) = 100%, Ca(O(2)) = 22.6 ml/dl). No significant differences were found for MVC and Q(tw) among the three Fi(O(2)) levels. In experiment 2, the subjects performed three sets of nine, intermittent, isometric, unilateral, submaximal quadriceps contractions (62% MVC followed by 1 MVC in each set) while breathing each Fi(O(2)). Q(tw) was assessed before and after exercise, and myoelectrical activity of the vastus lateralis was obtained during exercise. The percent reduction of twitch force (potentiated Q(tw)) in hypoxia (-27.0%) was significantly (P < 0.05) greater than in normoxia (-21.4%) and hyperoxia (-19.9%), as were the changes in intratwitch measures of contractile properties. The increase in integrated electromyogram over the course of the nine contractions in hypoxia (15.4%) was higher (P < 0.05) than in normoxia (7.2%) or hyperoxia (6.7%). These results demonstrate that quadriceps muscle fatigability during isolated muscle exercise is exacerbated in acute hypoxia, and these effects are independent of the relative exercise intensity.

Adult↗

PubMed2006

Effect of acute severe hypoxia on peripheral fatigue and endurance capacity in healthy humans.

We hypothesized that severe hypoxia limits exercise performance via decreased contractility of limb locomotor muscles. Nine male subjects [mean +/- SE maximum O(2) uptake (Vo(2 max)) = 56.5 +/- 2.7 ml x kg(-1) x min(-1)] cycled at > or =90% Vo(2 max) to exhaustion in normoxia [NORM-EXH; inspired O(2) fraction (Fi(O(2))) = 0.21, arterial O(2) saturation (Sp(O(2))) = 93 +/- 1%] and hypoxia (HYPOX-EXH; Fi(O(2)) = 0.13, Sp(O(2)) = 76 +/- 1%). The subjects also exercised in normoxia for a time equal to that achieved in hypoxia (NORM-CTRL; Sp(O(2)) = 96 +/- 1%). Quadriceps twitch force, in response to supramaximal single (nonpotentiated and potentiated 1 Hz) and paired magnetic stimuli of the femoral nerve (10-100 Hz), was assessed pre- and at 2.5, 35, and 70 min postexercise. Hypoxia exacerbated exercise-induced peripheral fatigue, as evidenced by a greater decrease in potentiated twitch force in HYPOX-EXH vs. NORM-CTRL (-39 +/- 4 vs. -24 +/- 3%, P < 0.01). Time to exhaustion was reduced by more than two-thirds in HYPOX-EXH vs. NORM-EXH (4.2 +/- 0.5 vs. 13.4 +/- 0.8 min, P < 0.01); however, peripheral fatigue was not different in HYPOX-EXH vs. NORM-EXH (-34 +/- 4 vs. -39 +/- 4%, P > 0.05). Blood lactate concentration and perceptions of limb discomfort were higher throughout HYPOX-EXH vs. NORM-CTRL but were not different at end-exercise in HYPOX-EXH vs. NORM-EXH. We conclude that severe hypoxia exacerbates peripheral fatigue of limb locomotor muscles and that this effect may contribute, in part, to the early termination of exercise.

Adult↗

PubMed2006

Arterial oxygenation influences central motor output and exercise performance via effects on peripheral locomotor muscle fatigue in humans.

Changing arterial oxygen content (C(aO(2))) has a highly sensitive influence on the rate of peripheral locomotor muscle fatigue development. We examined the effects of C(aO(2)) on exercise performance and its interaction with peripheral quadriceps fatigue. Eight trained males performed four 5 km cycling time trials (power output voluntarily adjustable) at four levels of C(aO(2)) (17.6-24.4 ml O(2) dl(-1)), induced by variations in inspired O(2) fraction (0.15-1.0). Peripheral quadriceps fatigue was assessed via changes in force output pre- versus post-exercise in response to supra-maximal magnetic femoral nerve stimulation (DeltaQ(tw); 1-100 Hz). Central neural drive during the time trials was estimated via quadriceps electromyogram. Increased C(aO(2)) from hypoxia to hyperoxia resulted in parallel increases in central neural output (43%) and power output (30%) during cycling and improved time trial performance (12%); however, the magnitude of DeltaQ(tw) (-33 to -35%) induced by the exercise was not different among the four time trials (P > 0.2). These effects of C(aO(2)) on time trial performance and DeltaQ(tw) were reproducible (coefficient of variation = 1-6%) over repeated trials at each F(IO(2)) on separate days. In the same subjects, changing C(aO(2)) also affected performance time to exhaustion at a fixed work rate, but similarly there was no effect of Delta C(aO(2)) on peripheral fatigue. Based on these results, we hypothesize that the effect of C(aO(2)) on locomotor muscle power output and exercise performance time is determined to a significant extent by the regulation of central motor output to the working muscle in order that peripheral muscle fatigue does not exceed a critical threshold.

Adult↗

PubMed2006

Effects of arterial oxygen content on peripheral locomotor muscle fatigue.

The effect of arterial O2 content (Ca(O2)) on quadriceps fatigue was assessed in healthy, trained male athletes. On separate days, eight participants completed three constant-workload trials on a bicycle ergometer at fixed workloads (314 +/- 13 W). The first trial was performed while the subjects breathed a hypoxic gas mixture [inspired O2 fraction (Fi(O2)) = 0.15, Hb saturation = 81.6%, Ca(O2) = 18.2 ml O2/dl blood; Hypo] until exhaustion (4.5 +/- 0.4 min). The remaining two trials were randomized and time matched with Hypo. The second and third trials were performed while the subjects breathed a normoxic (Fi(O2) = 0.21, Hb saturation = 95.0%, Ca(O2) = 21.3 ml O2/dl blood; Norm) and a hyperoxic (Fi(O2) = 1.0, Hb saturation = 100%, Ca(O2) = 23.8 ml O2/dl blood; Hyper) gas mixture, respectively. Quadriceps muscle fatigue was assessed via magnetic femoral nerve stimulation (1-100 Hz) before and 2.5 min after exercise. Myoelectrical activity of the vastus lateralis was obtained from surface electrodes throughout exercise. Immediately after exercise, the mean force response across 1-100 Hz decreased from preexercise values (P < 0.01) by -26 +/- 2, -17 +/- 2, and -13 +/- 2% for Hypo, Norm, and Hyper, respectively; each of the decrements differed significantly (P < 0.05). Integrated electromyogram increased significantly throughout exercise (P < 0.01) by 23 +/- 3, 10 +/- 1, and 6 +/- 1% for Hypo, Norm, and Hyper, respectively; each of the increments differed significantly (P < 0.05). Mean power frequency fell more (P < 0.05) during Hypo (-15 +/- 2%); the difference between Norm (-7 +/- 1%) and Hyper (-6 +/- 1%) was not significant (P = 0.32). We conclude that deltaCa(O2) during strenuous systemic exercise at equal workloads and durations affects the rate of locomotor muscle fatigue development.

Adult↗

PubMed2006

Predictive validity of ventilatory and lactate thresholds for cycling time trial performance.

PURPOSE: To determine which laboratory measurement best predicts 40 km cycling time-trial (TT) performance. METHODS: Fifteen male cyclists performed lactate-threshold (LT), ventilatory-threshold (VT), 5 km and 40 km TT. Key variables of interest were Watts at thresholds. For VT determination we used: breakpoint of ventilatory equivalent of oxygen (VE/VO2); breakpoint of ventilatory equivalent of carbon dioxide (VE/VCO2); V-slope; respiratory exchange ratio (RER)=1 and 0.95. For LT we used Stegmann's individual anaerobic threshold; the stage preceding the second 0.5 mmol L(-1) increase (Baldari); 4 mmol L(-1); 1 mmol L(-1) increase in 3 min; the stage preceding the first 1 mmol L(-1) increase as criterion methods (<1 mmol). Analyses also included peak power during the incremental threshold tests (MaxVT(watts), MaxLT(watts)) and 5 km performance (5K(avgwatts)). RESULTS: Regression analyses between VT variables and 40K(avgwatts) were significant for V-slope (r2=0.63), VE/VO2 (r2=0.64), RER(0.95) (r2=0.53), RER1 (r2=0.57), and MaxVT(watts) (r2=0.65). Regressions between LT variables and 40K(avgwatts) were significant for Baldari (r2=0.52), 4 mmol L(-1) (r2=0.36), <1 mmol (r2=0.35), Keul (r2=0.34), and MaxLT(watts) (r2=0.51). Regressions between 5K variables and 40K(avgwatts) were significant for 5K(avgwatts) (r2=0.58). Paired t-tests between these variables and the 40K(avgwatts) indicated that absolute power outputs at VE/VO2 (P=0.33), RER(0.95) (P=0.93), and 4 mmol L(-1) (P=0.39) were not significantly different from 40K(avgwatts). CONCLUSION: We conclude that VT-based variables are generally superior to LT variables relative to predicting 40K(avgwatts), the simplest of several valid measures appears to be VE/VO2.

Adult↗

PubMed2005

Muscle damage, fluid ingestion, and energy supplementation during recreational alpine skiing.

This study examined energy and fluid supplementation on indices of muscle damage during alpine skiing. Skiers were assigned to a carbohydrate-protein (CP), placebo (PL), or no fluid (NF) group. CP and PL ingested 1.62 L during and after skiing. Myoglobin did not change from pre-skiing (PS) to 2 h post-skiing (2PS) for CP (24.8 +/- 1.4 and 25.6 +/- 1.6 ng/mL), but rose significantly from 26.4 +/- 1.3 to 40.0 +/- 2.8 ng/mL for PL and from 29.0 +/- 1.3 to 82.9 +/- 3.6 ng/mL for NF. Creatine kinase was maintained from PRE to 2 PS for CP, but increased significantly from 117 +/- 7.2 to 174 +/- 43.4 U/L for PL and from 126 +/- 23.2 to 243 +/- 34.3 U/L for NF. This study demonstrates that ingestion of a CP beverage minimized muscle damage indices during skiing compared to PL and NF and that ingesting fluids may also minimize muscle damage compared to a NF condition.

Adult↗

PubMed2005

The contribution from shipping emissions to air quality and acid deposition in Europe.

A global three-dimensional Lagrangian chemistry-transport model STOCHEM is used to describe the European regional acid deposition and ozone air quality impacts along the Atlantic Ocean seaboard of Europe, from the SO2, NOx, VOCs and CO emissions from international shipping under conditions appropriate to the year 2000. Model-derived total sulfur deposition from international shipping reaches over 200 mg S m(-2) yr(-1) over the southwestern approaches to the British Isles and Brittany. The contribution from international shipping to surface ozone concentrations during the summertime, peaks at about 6 ppb over Ireland, Brittany and Portugal. Shipping emissions act as an external influence on acid deposition and ozone air quality within Europe and may require control actions in the future if strict deposition and air quality targets are to be met.

Acid Rain↗

PubMed2004

Influence of testing protocol on ventilatory thresholds and cycling performance.

PURPOSE: To compare the ventilatory response of two incremental exercise tests and determine their predictive validity on 40-km cycle time trial (40K) mean power output (40Kavgwatts). METHODS: Fifteen male cyclists performed two incremental exercise tests (T50x3:100 W +50 W x 3(-1) min, T25x1:20 W + 25 W x min(-1)) and a 40K over an 8-d period. Key variable was power at ventilatory threshold (VT). For VT determination during each test we used: VE/VO2 method, first clear breakpoint on the VE/VCO2 plot, V-slope method, RER = 1, and RER = 0.95. RESULTS: VO2max during T50x3 and T25x1 was not different (66.6 vs 67.6 mL x kg(-1) x min(-1)), although T25x1 peak power output (MaxT25x1; 402 W) was significantly higher than MaxT50x3 (363 W). T50x3 and T25x1 VT power outputs indicated that the power output at T25x1:RER = 1 and T25x1:RER = 0.95 were significantly higher compared with T50x3 (324 vs 304 W and 282 vs 264 W, respectively). Regression analyses between T50x3 variables and 40Kavgwatts were significant for T50x3:V-slope (R2 = 0.37; SEE 20.2 W), T50x3:VE/VO2 (R2 = 0.64; SEE 15.3 W), T50x3:RER = 0.95 (R2 = 0.42; SEE 19.4 W), T50x3:RER = 1 (R2 = 0.45; SEE 18.8 W), and MaxT50x3 (R2 = 0.51; SEE 17.8 W). Regression analyses between T25x1 variables and 40Kavgwatts were significant for T25x1:V-slope (R2 = 0.63; SEE 15.4 W), T25x1:VE/VO2 (R2 = 0.64; SEE 15.2 W), T25x1:RER = 0.95 (R2 = 0.53; SEE 17.4 W), T25x1:RER = 1 (R2 = 0.57; SEE 16.7 W), and MaxT25x1 (R2 = 0.65; SEE 15.0 W). There was no significant difference between 40Kavgwatts (282 W) and power outputs at T50x3:VE/VO2 (277 W), T50x3:V-slope (289 W), T25x1:VE/VO2 (276 W), and T25x1:RER = 0.95 (282 W). CONCLUSION: Generally, T25x1 based VT variables were superior to T50x3 variables regarding the prediction of 40Kavgwatts. We conclude that the VE/VO2 method is protocol independent and a valid 40Kavgwatts predictor.

Adult↗

PubMed2004

An evaluation of the predictive validity and reliability of ventilatory threshold.

PURPOSE: To identify a valid and reliable method to determine 40-km time trial (40K) performance in a laboratory setting. METHODS: Part 1: Ventilatory threshold (VT) and 40K performance were determined on two occasions (February/September) using two subsets of cyclists (N = 15 each; VO(2max) 67.6 +/- 4.2/71.5 +/- 3.0 mL x kg(-1) x min(-1)) to determine the predictive validity of VT assessments. Variables of interest were power output at VT, peak power output (MaxVT(w)), and average power output during 40K (40K(avgwatts)). For VT determination we used: breakpoint of VE/VO2; breakpoint of VE/VCO2; V-slope; RER = 1; and RER = 0.95. In part 2, test-retest reliability of VT and MaxVT(w) were examined in 20 subjects (VO(2max) 64.8 +/- 8.0 mL x kg(-1) x min(-1)) on two occasions, separated by 48 h. RESULTS: Regression analyses between power outputs at VTs and 40K(avgwatts) showed significant predictive validity for (February/September): V-slope (r = 0.79/0.84; SEE 155/13.3W), VE/VO2 (r = 0.80/0.81; SEE 15.2/14.2W), RER0.95 (r = 0.73/0.58; SEE 17.4/21.2W), RER1 (r = 0.75/0.74; SEE 16.8/16.7W), and MaxVT(w) (r = 0.81/0.73; SEE 15.0/17.1W). Paired t-tests between power outputs at VTs and the 40K(avgwatts) indicated that mean power outputs at VE/O2 (261 +/- 29W; P = 0.33) and RER0.95 (274 +/- 55W; P = 0.93) in February and VE/VO2 (274 +/- 37W; P = 0.79) in September were not significantly different from the respective 40K(avgwatts) (277 +/- 30W/281 +/- 30W). Test-retest reliability analysis yielded the following intraclass correlation and relative test-retest errors: V-slope: 0.98, 2.6%; VE/VO2: 0.95, 5.3%; RER0.95: 0.87, 9.8%; RER1: 0.94, 5.7%; VE/VCO2: 0.87, 12.1%; MaxVT(w): 0.98, 2.6%. CONCLUSION: The high test-retest reliability and consistent ability to accurately predict athletes' 40K(avgwatts) across a competitive season indicated that VE/VO2 was superior to the other evaluated methods.

Adult↗

PubMed2002

Changing trends in sulfur emissions in Asia: implications for acid deposition, air pollution, and climate.

In the early 1990s, it was projected that annual SO2 emissions in Asia might grow to 80-110 Tg yr(-1) by 2020. Based on new high-resolution estimates from 1975 to 2000, we calculate that SO2 emissions in Asia might grow only to 40-45 Tg yr(-1) by 2020. The main reason for this lower estimate is a decline of SO2 emissions from 1995 to 2000 in China, which emits about two-thirds of Asian SO2. The decline was due to a reduction in industrial coal use, a slowdown of the Chinese economy, and the closure of small and inefficient plants, among other reasons. One effect of the reduction in SO2 emissions in China has been a reduction in acid deposition not only in China but also in Japan. Reductions should also improve visibility and reduce health problems. SO2 emission reductions may increase global warming, but this warming effect could be partially offset by reductions in the emissions of black carbon. How SO2 emissions in the region change in the coming decades will depend on many competing factors (economic growth, pollution control laws, etc.). However a continuation of current trends would result in sulfur emissions lower than any IPCC forecasts.

Acid Rain↗