Skeletal muscle monocarboxylate transporter content is not different between black and white runners

The superior performance of black African runners has been associated with lower plasma lactate concentrations at sub-maximal intensities compared to white runners. The aim was to investigate the monocarboxylate transporters 1 (MCT1) and MCT4 content in skeletal muscle of black and white runners. Although black runners exhibited lower plasma lactate concentrations after maximum exercise (8.8 ± 2.0 vs. 12.3 ± 2.7 mmol l⁻¹, P < 0.05) and a tendency to be lower at 16 km h⁻¹ (2.4 ± 0.7 vs. 3.8 ± 2.4 mmol l⁻¹, P = 0.07) than the white runners, there were no differences in MCT1 or MCT4 levels between the two groups. For black and white runners together, MCT4 content correlated significantly with 10 km personal best time (r = −0.74, P < 0.01) and peak treadmill speed (r = 0.88, P < 0.001), but MCT1 content did not. Although whole homogenate MCT content was not different between the groups, more research is required to explain the lower plasma lactate concentrations in black runners.     

Changes in heart rate recovery after high-intensity training in well-trained cyclists

Heart rate recovery (HRR) after submaximal exercise improves after training. However, it is unknown if this also occurs in already well-trained cyclists. Therefore, 14 well-trained cyclists (VO_2max 60.3 ± 7.2 ml kg⁻¹ min⁻¹; relative peak power output 5.2 ± 0.6 W kg⁻¹) participated in a high-intensity training programme (eight sessions in 4 weeks). Before and after high-intensity training, performance was assessed with a peak power output test including respiratory gas analysis (VO_2max) and a 40-km time trial. HRR was measured after every high-intensity training session and 40-km time trial. After the training period peak power output, expressed as W kg⁻¹, improved by 4.7% (P = 0.000010) and 40-km time trial improved by 2.2% (P = 0.000007), whereas there was no change in VO_2max (P = 0.066571). Both HRR after the high intensity training sessions (7 ± 6 beats; P = 0.001302) and HRR after the 40-km time trials (6 ± 3 beats; P = 0.023101) improved significantly after the training period. Good relationships were found between improvements in HRR_40-km and improvements in peak power output (r = 0.73; P < 0.0001) and 40-km time trial time (r = 0.96; P < 0.0001). In conclusion, HRR is a sensitive marker which tracks changes in training status in already well-trained cyclists and has the potential to have an important role in monitoring and prescribing training.     

Longitudinal changes in haemoglobin mass and <Emphasis Type="Italic">V</Emphasis>O<Subscript>2max</Subscript> in adolescents

This study assessed the relationship between haemoglobin mass (Hb_mass) and maximum oxygen consumption (VO_2max) in adolescents over 1 year. Twenty-three subjects (11–15 years) participated; 12 undertook ~12 months of cycle training (cyclists) and 11 were sedentary (controls). Hb_mass and VO_2max were measured approximately every 3 months. At baseline there was a high correlation (r = 0.82, P < 0.0001) between relative VO_2max (ml kg⁻¹ min⁻¹) and relative Hb_mass (g kg⁻¹). During 12 months there was a significant increase in relative VO_2max of the cyclists but not the controls; however, there was no corresponding increase in relative Hb_mass of either group. The correlation between percent changes in relative VO_2max and relative Hb_mass was not significant for cyclists (r = 0.31, P = 0.33) or controls (r = 0.42, P = 0.19). Training does not increase relative Hb_mass in adolescents consistent with a strong hereditary role for Hb_mass and VO_2max. Hb_mass may be used to identify adolescents who have a high VO_2max.     

No case of exercise-associated hyponatraemia in top male ultra-endurance cyclists: the ‘Swiss Cycling Marathon’

The prevalence of exercise-associated hyponatraemia (EAH) has been investigated in endurance athletes such as runners and Ironman triathletes, but not in ultra-endurance road cyclists. We assessed fluid intake and changes in body mass, urine specific gravity and plasma sodium concentration ([Na⁺]) in 65 ultra-endurance road cyclists in a 720-km ultra-cycling marathon, the ‘Swiss Cycling Marathon’. The cyclists lost 1.5 (1.7)% body mass (P < 0.01). No athlete developed EAH. Fluid intake was associated with the change in plasma [Na⁺] (r = −0.32, P < 0.05) and the change in body mass (r = −0.30, P < 0.05). The change in plasma [Na⁺] was related to post-race plasma [Na⁺] (r = 0.63, P < 0.0001). To conclude, ad libitum fluid intake in ultra-endurance cyclists in a single-stage ultra-endurance road cycling race showed no case of EAH. Future studies regarding drinking behaviour in different ultra-endurance disciplines might give insights into why the prevalence of EAH is different in the different disciplines.     

Effect of heavy strength training on thigh muscle cross-sectional area, performance determinants, and performance in well-trained cyclists

The purpose of this study was to investigate the effect of heavy strength training on thigh muscle cross-sectional area (CSA), determinants of cycling performance, and cycling performance in well-trained cyclists. Twenty well-trained cyclists were assigned to either usual endurance training combined with heavy strength training [E + S; n = 11 (♂ = 11)] or to usual endurance training only [E; n = 9 (♂ = 7, ♀ = 2)]. The strength training performed by E + S consisted of four lower body exercises [3 × 4–10 repetition maximum (RM)], which were performed twice a week for 12 weeks. Thigh muscle CSA, maximal force in isometric half squat, power output in 30 s Wingate test, maximal oxygen consumption (VO_2max), power output at 2 mmol l⁻¹ blood lactate concentration ([la⁻]), and performance, as mean power production, in a 40-min all-out trial were measured before and after the intervention. E + S increased thigh muscle CSA, maximal isometric force, and peak power in the Wingate test more than E. Power output at 2 mmol l⁻¹ [la⁻] and mean power output in the 40-min all-out trial were improved in E + S (P < 0.05). For E, only performance in the 40-min all-out trial tended to improve (P = 0.057). The two groups showed similar increases in VO_2max (P < 0.05). In conclusion, adding strength training to usual endurance training improved determinants of cycling performance as well as performance in well-trained cyclists. Of particular note is that the added strength training increased thigh muscle CSA without causing an increase in body mass.     

Fatigue resistance during high-intensity intermittent exercise from childhood to adulthood in males and females

This study examined the maturation pattern of fatigue resistance (FR) from childhood to adulthood in females and males during high-intensity intermittent exercise and compared FR between females and males in childhood and adolescence. Thirty males (boys 11.3 ± 0.5 years, teen-males 14.7 ± 0.3 years, men 24.0 ± 2.1 years) and 30 females (girls 10.9 ± 0.6 years, teen-females 14.4 ± 0.7 years, women 25.2 ± 1.4) participated in this study. They performed high-intensity intermittent exercise (4 × 18 maximal knee flexions and extensions with 1-min rest) on an isokinetic dynamometer at 120°s⁻¹. Peak torque of flexors (PTFL) and extensors (PTEX), and total work (TW) were measured. FR was calculated as % of PTEX, PTFL, and TW in 4th versus 1st set. FR was greater (P < 0.05) in boys versus teen-males and men, and in teen-males versus men. In females, FR was greater (P < 0.05) in girls versus teen-females and women, but not different between teen-females and women. FR was not different in boys versus girls and in teen-males versus teen-females. FR for PTFL, PTEX, and TW correlated negatively (P < 0.001) with the respective peak values (r = −0.68 to −0.84), and FR for TW with peak lactate (r = −0.58 to −0.69). In addition, age correlated (P < 0.01) with FR for males (r = −0.75) and females (r = −0.55). In conclusion, FR during high-intensity intermittent exercise undergoes a gradual decline from childhood to adulthood in males, while in females the adult profile establishes at mid-puberty (14–15 years). The maturation profile of FR in males and females during development appears to reflect the maturation profiles of peak torque, short-term muscle power, and lactate concentration after exercise. T. Tsirini and A. Zafeiridis contributed equally to this work.     

Age,muscle fatigue,and walking endurance in pre-menopausal women

Aging is associated with loss of endurance; however, aging is also associated with decreased fatigue during maximal isometric contractions. The aims of this study were to examine the relationship between age and walking endurance (WE) and maximal isometric fatigue (MIF) and to determine which metabolic/fitness components explain the expected age effects on WE and MIF. Subjects were 96 pre-menopausal women. Oxygen uptake (walking economy) was assessed during a 3-mph walk; aerobic capacity and WE by progressive treadmill test; knee extension strength by isometric contractions, MIF during a 90-s isometric plantar flexion (muscle metabolism measured by ³¹P MRS). Age was related to increased walking economy (low VO₂, r = −0.19, P < 0.03) and muscle metabolic economy (force/ATP, 0.34, P = 0.01), and reduced MIF (−0.26, P < 0.03). However, age was associated with reduced WE (−0.28, P < 0.01). Multiple regression showed that muscle metabolic economy explained the age-related decrease in MIF (partial r for MIF and age −0.13, P = 0.35) whereas walking economy did not explain the age-related decrease in WE (partial r for WE and age −0.25, P < 0.02). Inclusion of VO_2max and knee endurance strength accounted for the age-related decreased WE (partial r for WE and age = 0.03, P > 0.80). In premenopausal women, age is related to WE and MIF. In addition, these results support the hypothesis that age-related increases in metabolic economy may decrease MIF. However, decreased muscle strength and oxidative capacity are related to WE.     

Influence of moderate hypoxia on tolerance to high-intensity exercise

It remains uncertain as how the reduction in systemic oxygen transport limits high-intensity exercise tolerance. 11 participants (5 males; age 35 ± 10 years; peak [(V)\dot]\textO₂ max {\dot{V}\text{O}}_{2} \max 3.5 ± 0.4 L min⁻¹) performed cycle ergometry to the limit of tolerance: (1) a ramp test to determine ventilatory threshold (VT) and peak [(V)\dot]\textO₂ {\dot{V}\text{O}}_{2} ; (2) three to four constant-load tests in order to model the linear P–t ⁻¹ relationship for estimation of intercept (critical power; CP) and slope (AWC). All tests were performed in a random order under moderate hypoxia (FiO₂ = 0.15) and normoxia. The linearity of the P–t ⁻¹ relationship was retained under hypoxia, with a systematic reduction in CP (220 ± 25 W vs. 190 ± 28 W; P < 0.01) but no significant difference in AWC (11.7 ± 5.5 kJ vs. 12.1 ± 4.4 kJ; P > 0.05). However, large individual variations in the change of the latter were observed (−36 to +66%). A significant relationship was found between the % change in CP (r = 0.80, P < 0.01) and both peak [(V)\dot]\textO₂ {\dot{V}\text{O}}_{2} (CP: r = −0.65, P < 0.05) and VT values recorded under normoxia (CP: r = −0.65, P < 0.05). The present study demonstrates the aerobic nature of the intercept of the P–t ⁻¹ relationship, i.e. CP. However, the extreme within-individual changes in AWC do not support the original assumption that AWC reflects a finite energy store. Lower hypoxia-induced decrements in CP were observed in aerobically fitter participants. This study also demonstrates the greater ability these participants have to exercise at supra-CP but close to CP workloads under moderate hypoxia.     

Complete correction of anemia by erythropoiesis-stimulating agents is associated with insulin resistance in hemodialysis patients

Insulin resistance and anemia secondary to erythropoietin deficiency characterize patients with end-stage kidney disease. In a cross-sectional analysis, we examined the relationship between erythropoietin-mediated correction of anemia and insulin sensitivity in nondiabetic hemodialysis patients. Insulin sensitivity (euglycemic-hyperinsulinemic clamp) and endogenous glucose production (primed-continuous infusion of [6,6-²H₂]glucose) were determined in two groups of patients with normal hemoglobin (n:8; mean hemoglobin: 14.0 ± 0.3 g/dl) or with mild anemia (n:10; mean hemoglobin: 12.1 ± 0.9 g/dl). The patients with normal hemoglobin were receiving higher (P < 0.05) erythropoietin doses than those with mild anemia (171 ± 73 and 91 ± 39 U kg⁻¹ wk⁻¹, respectively). The two groups were matched for all other potential determinants of insulin resistance. Endogenous glucose production was similar in the two groups of patients in the postabsorptive state and was completely suppressed by insulin infusion. During the hyperinsulinemic clamp, the rate of glucose infusion to maintain euglycemia was significantly lower (P < 0.01) in the patients with normal hemoglobin levels [166 ± 31 mg (m²)⁻¹ min⁻¹] than in those with mild anemia [251 ± 49 mg (m²)⁻¹ min⁻¹] and in a group of matched controls [275 ± 68 mg (m²)⁻¹ min⁻¹]. In pooled patients, individual values of hemoglobin concentrations inversely correlated with the rates of insulin-mediated glucose infusion, both as absolute values (r = −0.58; P < 0.05) and as values normalized by steady-state plasma insulin concentration (r = −0.74; P < 0.001). In conclusion, this exploratory study indicates that complete correction of anemia by erythropoietin treatment in patients with end-stage kidney disease on hemodialysis is associated with impaired insulin sensitivity.     

Syncope is unrelated to supine and postural hypotension following prolonged exercise

Syncope is widely reported following prolonged exercise. It is often assumed that the magnitude of exercise-induced hypotension (post-exercise hypotension; PEH), and the hypotensive response to postural change (initial orthostatic hypotension; IOH) are predictors of syncope post-exercise. The aim of this study was to determine the relationship between PEH, IOH, the residual IOH and syncope following prolonged exercise. Blood pressure (BP; Finometer) was measured continuously in 19 athletes (47 ± 20 years; BMI: 23.2 ± 2.2 kg m²; [(V)\dot] \dot{V} O₂ max: 51.3 ± 10.8 mL kg⁻¹ min⁻¹) whilst supine and during head-up tilt (HUT) to 60° for 15 min (or to syncope), prior to and following 4 h of running at 70–80% maximal heart rate. Syncope developed in 15 of 19 athletes post-exercise [HUT-time completed, Pre: 14:39 (min:s) ± 0:55; Post: 5:59 ± 4:53; P < 0.01]. PEH was apparent (−7 ± 7 mmHg; −8 ± 8%), but was unrelated to HUT-time completed (r ² = 0.09; P > 0.05). Although the magnitude of IOH was similar to post-exercise [−28 ± 12 vs. −20 ± 14% (pre-exercise); P > 0.05], the BP recovery following IOH was incomplete [−9 ± 9 vs. −1 ± 11 (pre-exercise); P < 0.05]; however, neither showed a relation to HUT-time completed (r ² = 0.18, r ² = 0.01; P > 0.05, respectively). Although an inability to maintain BP is a common feature of syncope post-exercise, the magnitude of PEH, IOH and residual IOH do not predict time to syncope. Practically, endurance athletes who present with greater hypotension are not necessarily at a greater risk of syncope than those who present with lesser reductions in BP.     

Performance and thermoregulatory effects of chronic bupropion administration in the heat

The combination of acute dopamine/noradrenaline reuptake inhibition (bupropion; BUP) and heat stress (30°C) significantly improves performance (9%). Furthermore the maintenance of a higher power output resulted in the attainment of significantly higher heart rates and rectal temperatures—above 40°C—in the BUP trial compared to the placebo trial. Since BUP is an aid to cease smoking that is taken for longer periods, question remains if similar performance and thermoregulatory effects are found following administration of BUP over several days (10 days). The purpose of the present study was to examine the effects of chronic BUP on exercise performance, thermoregulation and hormonal variables in the heat. Eight trained male cyclists participated in the study. Subjects completed two trials consisting of 60 min fixed intensity exercise (55% W _max) followed by a time trial (TT) in a double-blind randomized crossover design. Exercise was performed in 30°C. Subjects took either placebo (PLAC) or BUP (Zyban™) for 3 days (150 mg), followed by 300 mg for 7 days. Chronic BUP did not influence TT performance (BUP 40′42″ ± 4′18″; PLAC 41′36″ ± 5′12″), but significantly increased core temperature (P = 0.030). BUP significantly increased circulating growth hormone levels (PLAC: 9.8 ± 5.8 ng L⁻¹; BUP: 13 ± 6.8 ng L⁻¹; P < 0.008). Discussion/conclusion: Chronic BUP did not influence TT performance in 30°C and subjects did not reach core temperature values as high as observed during the acute BUP study. It seems that chronic administration results in an adaptation of central neurotransmitter homeostasis, resulting in a different response to the drug.     

Light-intensity activities are important for estimating physical activity energy expenditure using uniaxial and triaxial accelerometers

This study evaluated the validity of the total energy expenditure (TEE) estimated using uniaxial (ACCuni) and triaxial (ACCtri) accelerometers in the elderly. Thirty-two healthy elderly (64–87 years) participated in this study. TEE was measured using the doubly labeled water (DLW) method (TEE_DLW). TEE_ACCuni (6.79 ± 1.08 MJ day⁻¹) was significantly lower than TEE_DLW (7.85 ± 1.54 MJ day⁻¹) and showed wider limits of agreement (−3.15 to 1.12 MJ day⁻¹) with a smaller correlation coefficient (r = 0.703). TEE_ACCtri (7.88 ± 1.27 MJ day⁻¹) did not differ from TEE_DLW and showed narrower limits of agreement (−1.64 to 1.72 MJ day⁻¹) with a larger correlation coefficient (r = 0.835, P < 0.001). The estimated intensities of light activities were significantly lower with ACCuni. Greater mediolateral acceleration was observed during 6-min walk tests. The results suggest that ACCtri is a better choice than ACCuni for assessing TEE in the elderly.     

Lung oxidative stress as related to exercise and altitude. Lipid peroxidation evidence in exhaled breath condensate: a possible predictor of acute mountain sickness

Lung oxidative stress (OS) was explored in resting and in exercising subjects exposed to moderate and high altitude. Exhaled breath condensate (EBC) was collected under field conditions in male high-competition mountain bikers performing a maximal cycloergometric exercise at 670 m and at 2,160 m, as well as, in male soldiers climbing up to 6,125 m in Northern Chile. Malondialdehyde concentration [MDA] was measured by high-performance liquid chromatography in EBC and in serum samples. Hydrogen peroxide concentration [H₂O₂] was analysed in EBC according to the spectrophotometric FOX₂ assay. [MDA] in EBC of bikers did not change while exercising at 670 m, but increased from 30.0±8.0 to 50.0±11.0 nmol l⁻¹ (P<0.05) at 2,160 m. Concomitantly, [MDA] in serum and [H₂O₂] in EBC remained constant. On the other hand, in mountaineering soldiers, [H₂O₂] in EBC under resting conditions increased from 0.30±0.12 μmol l⁻¹ at 670 m to 1.14±0.29 μmol l⁻¹ immediately on return from the mountain. Three days later, [H₂O₂] in EBC (0.93 ±0.23 μmol l⁻¹) continued to be elevated (P<0.05). [MDA] in EBC increased from 71±16 nmol l⁻¹ at 670 m to 128±26 nmol l⁻¹ at 3,000 m (P<0.05). Changes of [H₂O₂] in EBC while ascending from 670 m up to 3,000 m inversely correlated with concomitant variations in HbO2 saturation (r=−0.48, P<0.05). AMS score evaluated at 5,000 m directly correlated with changes of [MDA] in EBC occurring while the subjects moved from 670 to 3,000 m (r=0.51, P<0.05). Lung OS may constitute a pathogenic factor in AMS.     

10 or 30-s sprint interval training bouts enhance both aerobic and anaerobic performance

We assessed whether 10-s sprint interval training (SIT) bouts with 2 or 4 min recovery periods can improve aerobic and anaerobic performance. Subjects (n = 48) were assigned to one of four groups [exercise time (s):recovery time (min)]: (1) 30:4, (2) 10:4, (3) 10:2 or (4) control (no training). Training was cycling 3 week⁻¹ for 2 weeks (starting with 4 bouts session⁻¹, increasing 1 bout every 2 sessions, 6 total). Pre- and post-training measures included: VO_2max, 5-km time trial (TT), and a 30-s Wingate test. All groups were similar pre-training and the control group did not change over time. The 10-s groups trained at a higher intensity demonstrated by greater (P < 0.05) reproducibility of peak (10:4 = 96%; 10:2 = 95% vs. 30:4 = 89%), average (10:4 = 84%; 10:2 = 82% vs. 30:4 = 58%), and minimum power (10:4 = 73%; 10:2 = 69%; vs. 30:4 = 40%) within each session while the 30:4 group performed ~2X (P < 0.05) the total work session⁻¹ (83–124 kJ, 4–6 bouts) versus 10:4 (38–58 kJ); 10:2 (39–59 kJ). Training increased TT performance (P < 0.05) in the 30:4 (5.2%), 10:4 (3.5%), and 10:2 (3.0%) groups. VO_2max increased in the 30:4 (9.3%) and 10:4 (9.2%), but not the 10:2 group. Wingate peak power kg⁻¹ increased (P < 0.05) in the 30:4 (9.5%), 10:4 (8.5%), and 10:2 (4.2%). Average Wingate power kg⁻¹ increased (P < 0.05) in the 30:4 (12.1%) and 10:4 (6.5%) groups. These data indicate that 10-s (with either 2 or 4 min recovery) and 30-s SIT bouts are effective for increasing anaerobic and aerobic performance.     

Relevance of individual characteristics for thermoregulation during exercise in a hot-dry environment

The aim of this study was to investigate the relevance of individual characteristics for thermoregulation during prolonged cycling in the heat. For this purpose, 28 subjects cycled for 60 min at 60% VO_2peak in a hot-dry environment (36 ± 1°C; 25 ± 2% relative humidity, airflow 2.5 m/s). Subjects had a wide range of body mass (99–43 kg), body surface area (2.2–1.4 m²), body fatness (28–5%) and aerobic fitness level (VO_2peak = 5.0–2.1 L/min). At rest and during exercise, rectal and mean skin temperatures were measured to calculate the increase in body temperature (ΔT _body) during the trial. Net metabolic heat production (M _NET) and potential heat loss (by means of evaporation, radiation and convection) were calculated. Although subjects exercised at the same relative intensity, ΔT _body presented high between-subjects variability (range from 0.44 to 1.65°C). ΔT _body correlated negatively with body mass (r = −0.49; P < 0.01), body surface area (r = −0.47; P < 0.01) and T_body at rest (r = −0.37; P < 0.05), but it did not significantly correlate with body fatness (r = 0.12; P > 0.05). ΔT _body positively correlated with the body surface area/mass ratio (r = 0.46; P < 0.01) and the difference between M _NET and potential heat loss (r = 0.56; P < 0.01). In conclusion, a large body size (mass and body surface area) is beneficial to reduce ΔT _body during cycling exercise in the heat. However, subjects with higher absolute heat production (more aerobically fit) accumulate more heat because heat production may exceed potential heat loss (uncompensability).     

Effects of athletes’ muscle mass on urinary markers of hydration status

To determine if athletes’ muscle mass affects the usefulness of urine specific gravity (U _sg) as a hydration index. Nine rugby players and nine endurance runners differing in the amount of muscle mass (42 ± 6 vs. 32 ± 3 kg, respectively; P = 0.0002) were recruited. At waking during six consecutive days, urine was collected for U _sg analysis, urine osmolality (U _osm), electrolytes ( \mathop U\nolimits_{[\textNa ⁺ ]} {\mathop U\nolimits_{[{\text{Na}}^{ + } ]} }, \mathop U\nolimits_{[\textK ⁺ ]} {\mathop U\nolimits_{[{\text{K}}^{ + } ]} } and \mathop U\nolimits_{[\textCl ^- ]} {\mathop U\nolimits_{[{\text{Cl}}^{ - } ]} }) and protein metabolites (U _[Creatinine], U _[Urea] and U _{[Uric acid]}) concentrations. In addition, fasting blood serum osmolality (S _osm) was measured on the sixth day. As averaged during 6 days, U _sg (1.021 ± 0.002 vs. 1.016 ± 0.001), U _osm (702 ± 56 vs. 554 ± 41 mOsmol kg⁻¹ H₂O), U _[Urea] (405 ± 36 vs. 302 ± 23 mmol L⁻¹) and U _{[Uric acid]} (2.7 ± 0.3 vs. 1.7 ± 0.2 mmol L⁻¹) were higher in rugby players than runners (P < 0.05). However, urine electrolyte concentrations were not different between groups. A higher percentage of rugby players than runners (56 vs. 11%; P = 0.03) could be cataloged as hypohydrated by U _sg (i.e., >1.020) despite S _osm being below 290 mOsmol kg⁻¹ H₂O in all participants. A positive correlation was found between muscle mass and urine protein metabolites (r = 0.47; P = 0.04) and between urine protein metabolites and U _sg (r = 0.92; P < 0.0001). In summary, U _sg specificity to detect hypohydration was reduced in athletes with large muscle mass. Our data suggest that athletes with large muscle mass (i.e., rugby players) are prone to be incorrectly classified as hypohydrated based on U _sg.     

Muscle metabolic, enzymatic and transporter responses to a session of prolonged cycling

A single session of prolonged work was employed to investigate changes in selected metabolic, transporter and enzymatic properties in muscle. Ten active but untrained volunteers (weight = 73.9 ± 4.2 kg) with a peak aerobic power ( [(V)\dot]\textO_2\textpeak ) \left( {\dot{V}{\text{O}}_{{2{\text{peak}}}} } \right) of 2.95 ± 0.27 l min⁻¹, cycled for 2 h at 62 ± 1.3% ( [(V)\dot]\textO_2\textpeak ) \left( {\dot{V}{\text{O}}_{{2{\text{peak}}}} } \right) Tissue extraction from the vastus lateralis occurred prior to (E1-Pre) and following (E1-Post) exercise and on 3 consecutive days of recovery (R1, R2, R3). The exercise resulted in decreases (P < 0.05) in ATP (−9.3%) and creatine phosphate (−49%) and increases in lactate (+100%), calculated free ADP (+253%) and free AMP (+1,207%), all of which recovered to E1-Pre by R1. Glycogen concentration, which was depressed (P < 0.05) by 75% at E1-Post, did not recover until R3. Compared to E1-Pre, the cycling also resulted in decreases (P < 0.05) in the activities of cytochrome c oxidase, phosphorylase, and hexokinase but not in citrate synthase (CS) or 3-hydroxy-CoA dehydrogenase at E1-Post. With the exception of CS, which was elevated (P < 0.05) at R3, all enzyme activities were not different from E1-Pre during recovery. For the glucose (GLUT1, GLUT4) and monocarboxylate (MCT1, MCT4) transporters, changes in expression levels (P < 0.05) were only observed for GLUT1 at R1 (+42%) and R3 (+33%). It is concluded that the metabolic stress produced by prolonged exercise is reversed by 1 day of recovery. One day of exercise also resulted in a potential upregulation in the citric acid cycle and glucose transport capabilities, adaptations which are expressed at variable recovery durations.     

Sweat sodium concentration during exercise in the heat in aerobically trained and untrained humans

The purpose of this study was to determine whether sweat sodium concentration ([Na⁺]_sweat) during exercise in the heat differs between aerobically trained and untrained individuals. On three occasions, ten endurance-trained (Tr) and ten untrained (UTr) subjects ( [(V)\dot]\textO_2\textpeak \dot{V}{\text{O}}_{{2{\text{peak}}}}  = 4.0 ± 0.8 vs. 3.4 ± 0.7 L min⁻¹, respectively; P < 0.05) cycled in a hot-ventilated environment (36 ± 1°C; 25 ± 2% humidity, airflow 2.5 m s⁻¹) at three workloads (i.e., 40, 60, and 80% [(V)\dot]\textO_2\textpeak \dot{V}{\text{O}}_{{2{\text{peak}}}} ). Whole-body (SR_WB) and back sweat rates (SR_BACK) were measured. At the conclusion of the study, Na⁺ in sweat and blood samples was analyzed to calculate Na⁺ secretion and reabsorption rates. SR_WB and SR_BACK were highly correlated in Tr and UTr (r = 0.74 and 0.79, respectively; P < 0.0001). In both groups, SR_BACK increased with the increases in exercise intensity (P < 0.05). Likewise, [Na⁺]_sweat increased with the exercise intensity in both groups (P < 0.05) and it tended to be higher in Tr than in UTr at 60 and 80% [(V)\dot]\textO_2\textpeak \dot{V}{\text{O}}_{{2{\text{peak}}}} (~22 mmol L⁻¹ higher; P = 0.06). However, when normalized for SR_BACK, [Na⁺]_sweat was not different between groups. In both groups, Na⁺ secretion and reabsorption rates increased with the increases in SR_BACK (P < 0.05). However, Na⁺ reabsorption rate was lower in the Tr than in the UTr (mean slope = 48 vs. 82 ηmol cm⁻² min⁻¹; P = 0.03). In conclusion, using a cross-sectional study design, our data suggest that aerobic fitness level does not reduce sweat Na⁺ secretion or enhance Na⁺ reabsorption during prolonged exercise in the heat that induced high sweat rates.     

High mobility group box protein-1 correlates with microinflammatory state and nutritional status in continuous ambulatory peritoneal dialysis patients

High mobility group box protein-1 (HMGB-1) was recently identified as a new type of inflammatory cytokine. Inflammation can lead to malnutrition to some extent. Our study was aimed to clarify the relationship between serum HMGB-1 level with microinflammatory state and nutritional status in continuous ambulatory peritoneal dialysis (CAPD) patients. Patients in the treatment of maintenance of peritoneal dialysis for >6 months were included. HMGB-1, interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) were measured by enzyme-linked immunosorbent assay (ELISA). High-sensitivity C-reactive-protein (hs-CRP), prealbumin (PA), serum albumin (S-Alb), hemoglobin (Hb), subjective global nutritional assessment (SGA), and CAPD presents’ urea clearance rate (Kt/V), creatinine clearance (CrCl), residual glomerular filtration rate (rGFR), and dialysate-to-plasma ratio of creatinine after 4 h (D/P_4Cr) were analyzed. The Independent-samples t test and Pearson’s rank correlation test were used. Serum HMGB-1, IL-6, and TNF-α of CAPD patients were significantly higher than in the control group (P < 0.05); Serum HMGB-1 levels had positive relationships with TNF-α (r = 0.730, P < 0.01), hs-CRP (r = 0.361, P < 0.01), and IL-6 (r = 0.865, P < 0.01), and had negative relationships with Hb (r = −0.59, P < 0.01), Alb (r = −0.34, P < 0.05), and PA (r = −0.44, P < 0.01); no significant relationships were found between serum HMGB-1 with SGA, peritoneal dialysis age, Kt/V, CrCl, rGFR, and D/P_4Cr. Our study revealed that HMGB-1 was elevated significantly in CAPD patients and correlated with indicators of inflammation and malnutrition. Serum HMGB-1 could be used as a marker for evaluating inflammation and malnutrition in CAPD patients.     

The effects of 6-week-decoupled bi-pedal cycling on submaximal and high intensity performance in competitive cyclists and triathletes

Aim of this work was to examine the effects of decoupled two-legged cycling on (1) submaximal and maximal oxygen uptake, (2) power output at 4 mmol L⁻¹ blood lactate concentration, (3) mean and peak power output during high intensity cycling (30 s sprint) and (4) isometric and dynamic force production of the knee extensor and flexor muscles. 18 highly trained male competitive male cyclists and triathletes (age 24 ± 3 years; body height 179 ± 11 cm; body mass 78 ± 8 kg; peak oxygen uptake 5,070 ± 680 mL min⁻¹) were equally randomized to exercise on a stationary cycle equipped either with decoupled or with traditional crank system. The intervention involved 1 h training sessions, 5 times per week for 6 weeks at a heart rate corresponding to 70% of VO_2peak. VO₂ at 100, 140, 180, 220 and 260 and power output at 4 mmol L⁻¹ blood lactate were determined during an incremental test. VO_2peak was recorded during a ramp protocol. Mean and peak power output were assessed during a 30 s cycle sprint. The maximal voluntary isometric strength of the quadriceps and biceps femoris muscles was obtained using a training machine equipped with a force sensor. No differences were observed between the groups for changes in any variable (P = 0.15–0.90; effect size = 0.00–0.30). Our results demonstrate that a 6 week (30 sessions) training block using decoupled crank systems does not result in changes in any physiological or performance variables in highly trained competitive cyclists.