Health and performance effects of 12 weeks of small-sided street football training compared to grass football training in habitually active young men.

PURPOSE: The purpose of the present study was to investigate the health and exercise performance effects of street football training on very small pitches surrounded by boards in young habitually active men in comparison to small-sided football training on grass. METHODS: Thirty-nine habitually active men (30.7 ± 6.7 years, 90.9 ± 16.6 kg, 183.8 ± 4.5 cm, 39.6 ± 6.0 mL/min/kg) were randomly assigned to a street football training group (ST) or grass football group (GR) playing small-sided games for 70 min, 1.5 and 1.7 times per week for 12 weeks, respectively, or an inactive control group (CO). Intensity during training was measured using heart rate (HR) and GPS units. Pre- and post-intervention, a test battery was completed. RESULTS: Mean HR (87.1 ± 5.0 vs. 84.0 ± 5.3%HRmax; P > 0.05) and percentage of training time above 90%HRmax (44 ± 28 vs. 34 ± 24%; P > 0.05) were not different between ST and GR. VO2max increased (P < 0.001) by 3.6[95% CI 1.8;5.4]mL/min/kg in GR with no significant change in ST or CO. HR during running at 8 km/h decreased (P < 0.001) by 14[10;17]bpm in ST and by 12[6;19]bpm in GR, with no change in CO. No changes were observed in blood pressure, resting HR, total body mass, lean body mass, whole-body bone mineral density, fasting blood glucose, HbA1c, plasma insulin, total cholesterol(C), LDL-C or HDL-C. Moreover, no changes were observed in Yo-Yo IE2 performance, 30-m sprint time, jump length or postural balance. CONCLUSION: Small-sided street football training for 12 weeks with 1-2 weekly sessions led to improvements in submaximal exercise capacity only, whereas recreational grass football training confirmed previous positive effects on submaximal exercise capacity as well as cardiorespiratory fitness.

Bone mineral density in lifelong trained male football players compared with young and elderly untrained men.

PURPOSE: The purpose of the present controlled cross-sectional study was to investigate proximal femur and whole-body bone mineral density (BMD), as well as bone turnover profile, in lifelong trained elderly male football players and young elite football players compared with untrained age-matched men. METHODS: One hundred and forty healthy, non-smoking men participated in the study, including lifelong trained football players (FTE, n = 35) aged 65-80 years, elite football players (FTY, n = 35) aged 18-30 years, as well as untrained age-matched elderly (UE, n = 35) and young (UY, n = 35) men. All participants underwent a regional dual-energy X-ray Absorptiometry (DXA) scan of the proximal femur and a whole-body DXA scan to determine BMD. From a resting blood sample, the bone turnover markers (BTMs) osteocalcin, carboxy-terminal type-1 collagen crosslinks (CTX-1), procollagen type-1 amino-terminal propeptide (P1NP), and sclerostin were measured. RESULTS: FTE had 7.3%-12.9% higher (p < 0.05) BMD of the femoral neck, wards, shaft, and total proximal femur in both legs compared to UE, and 9.3%-9.7% higher (p < 0.05) BMD in femoral trochanter in both legs compared to UY. FTY had 24.3%-37.4% higher (p < 0.001) BMD in all femoral regions and total proximal femur in both legs compared to UY. The whole-body DXA scan confirmed these results, with FTE showing similar whole-body BMD and 7.9% higher (p < 0.05) leg BMD compared to UY, and with FTY having 9.6% higher (p < 0.001) whole-body BMD and 18.2% higher (p < 0.001) leg BMD compared to UY. The plasma concentration of osteocalcin, CTX-1, and P1NP were 29%, 53%, and 52% higher (p < 0.01), respectively, in FTY compared to UY. CONCLUSION: BMD of the proximal femur and whole-body BMD are markedly higher in lifelong trained male football players aged 65-80 years and young elite football players aged 18-30 years compared to age-matched untrained men. Elderly football players even show higher BMD in femoral trochanter and leg BMD than untrained young despite an age difference of 47 years.

Muscle interstitial ATP and norepinephrine concentrations in the human leg during exercise and ATP infusion.

ATP has been proposed to play multiple roles in local skeletal muscle blood flow regulation by inducing vasodilation and modulating sympathetic vasoconstrictor activity, but the mechanisms remain unclear. Here we evaluated the effects of arterial ATP infusion and exercise on leg muscle interstitial ATP and norepinephrine (NE) concentrations to gain insight into the interstitial and intravascular mechanisms by which ATP causes muscle vasodilation and sympatholysis. Leg hemodynamics and muscle interstitial nucleotide and NE concentrations were measured during 1) femoral arterial ATP infusion (0.42 +/- 0.04 and 2.26 +/- 0.52 micromol/min; mean +/- SE) and 2) one-leg knee-extensor exercise (18 +/- 0 and 37 +/- 2 W) in 10 healthy men. Arterial ATP infusion and exercise increased leg blood flow (LBF) in the experimental leg from approximately 0.3 l/min at baseline to 4.2 +/- 0.3 and 4.6 +/- 0.5 l/min, respectively, whereas it was reduced or unchanged in the control leg. During arterial ATP infusion, muscle interstitial ATP, ADP, AMP, and adenosine concentrations remained unchanged in both legs, but muscle interstitial NE increased from approximately 5.9 nmol/l at baseline to 8.3 +/- 1.2 and 8.7 +/- 0.7 nmol/l in the experimental and control leg, respectively (P < 0.05), in parallel to a reduction in arterial pressure (P < 0.05). During exercise, however, interstitial ATP, ADP, AMP, and adenosine concentrations increased in the contracting muscle (P < 0.05), but not in inactive muscle, whereas interstitial NE concentrations increased similarly in both active and inactive muscles. These results suggest that the vasodilatory and sympatholytic effects of intraluminal ATP are mainly mediated via endothelial purinergic receptors. Intraluminal ATP and muscle contractions appear to modulate sympathetic nerve activity by inhibiting the effect of NE rather than blunting its local concentration.

Effect of dexamethasone on skeletal muscle Na+,K+ pump subunit specific expression and K+ homeostasis during exercise in humans.

The effect of dexamethasone on Na(+),K(+) pump subunit expression and muscle exchange of K(+) during exercise in humans was investigated. Nine healthy male subjects completed a randomized double blind placebo controlled protocol, with ingestion of dexamethasone (Dex: 2 x 2 mg per day) or placebo (Pla) for 5 days. Na(+),K(+) pump catalytic alpha1 and alpha2 subunit expression was approximately 17% higher (P < 0.05) and the structural beta1 and beta2 subunit expression was approximately 6-8% higher (P < 0.05) after Dex compared with Pla. During one-legged knee-extension for 10 min at low intensity (LI; 18.6 +/- 1.0 W), two moderate intensity (51.7 +/- 2.4 W) exercise bouts (MI(1): 5 min; 2 min recovery; MI(2): exhaustive) and two high-intensity (71.7 +/- 2.5 W) exercise bouts (HI(1): 1 min 40 s; 2 min recovery; HI(2): exhaustive), femoral venous K(+) was lower (P < 0.05) in Dex compared with Pla. Thigh K(+) release was lower (P < 0.05) in Dex compared with Pla in LI and MI, but not in HI. Time to exhaustion in MI(2) tended to improve (393 +/- 50 s versus 294 +/- 41 s; P = 0.07) in Dex compared with Pla, whereas no difference was detected in HI(2) (106 +/- 10 s versus 108 +/- 9 s). The results indicate that an increased Na(+),K(+) pump expression per se is of importance for thigh K(+) reuptake at the onset of low and moderate intensity exercise, but less important during high intensity exercise.

Effect of two different intense training regimens on skeletal muscle ion transport proteins and fatigue development.

This study examined the effect of two different intense exercise training regimens on skeletal muscle ion transport systems, performance, and metabolic response to exercise. Thirteen subjects performed either sprint training [ST; 6-s sprints (n = 6)], or speed endurance training [SET; 30-s runs approximately 130% Vo(2 max), n = 7]. Training in the SET group provoked higher (P < 0.05) plasma K(+) levels and muscle lactate/H(+) accumulation. Only in the SET group was the amount of the Na(+)/H(+) exchanger isoform 1 (31%) and Na(+)-K(+)-ATPase isoform alpha(2) (68%) elevated (P < 0.05) after training. Both groups had higher (P < 0.05) levels of Na(+)-K(+)-ATPase beta(1)-isoform and monocarboxylate transporter 1 (MCT1), but no change in MCT4 and Na(+)-K(+)-ATPase alpha(1)-isoform. Both groups had greater (P < 0.05) accumulation of lactate during exhaustive exercise and higher (P < 0.05) rates of muscle lactate decrease after exercise. The ST group improved (P < 0.05) sprint performance, whereas the SET group elevated (P < 0.05) performance during exhaustive continuous treadmill running. Improvement in the Yo-Yo intermittent recovery test was larger (P < 0.05) in the SET than ST group (29% vs. 10%). Only the SET group had a decrease (P < 0.05) in fatigue index during a repeated sprint test. In conclusion, turnover of lactate/H(+) and K(+) in muscle during exercise does affect the adaptations of some but not all related muscle ion transport proteins with training. Adaptations with training do have an effect on the metabolic response to exercise and specific improvement in work capacity.

Effects of high-intensity intermittent training on potassium kinetics and performance in human skeletal muscle.

A rise in extracellular potassium concentration in human skeletal muscle may play an important role in development of fatigue during intense exercise. The aim of the present study was to examine the effect of intense intermittent training on muscle interstitial potassium kinetics and its relationship to the density of Na(+),K(+)-ATPase subunits and K(ATP) channels, as well as exercise performance, in human skeletal muscle. Six male subjects performed intense one-legged knee-extensor training for 7 weeks. On separate days the trained leg (TL) and the control leg (CL) performed a 30 min exercise period of 30 W and an incremental test to exhaustion. At frequent intervals during the exercise periods interstitial potassium ([K(+)](I)) was determined by microdialysis, femoral arterial and venous blood samples were drawn and thigh blood flow was measured. Time to fatigue for TL was 28% longer (P < 0.05) than for CL (10.6 +/- 0.7 (mean +/-s.e.m.) versus 8.2 +/- 0.7 min). The amounts of Na(+),K(+)-ATPase alpha(1) and alpha(2) subunits were, respectively, 29.0 +/- 8.4 and 15.1 +/- 2.7% higher (P < 0.05) in TL than in CL, while the amounts of beta(1) subunits and ATP-dependent K(+) (K(ATP)) channels were the same. In CL [K(+)](I) increased more rapidly and was higher (P < 0.05) throughout the 30 W exercise bout, as well at 60 and 70 W, compared to TL, whereas [K(+)](I) was similar at the point of fatigue (9.9 +/- 0.7 and 9.1 +/- 0.5 mmol l(-1), respectively). During the 30 W exercise bouts and at 70 W during the incremental exercise femoral venous potassium concentration ([K(+)](v)) was higher (P < 0.05) in CL than in TL, but identical at exhaustion (6.2 +/- 0.2 mmol l(-1)). Release of potassium to the blood was not different in the two legs. The present data demonstrated that intense intermittent training reduce accumulation of potassium in human skeletal muscle interstitium during exercise, probably through a larger re-uptake of potassium due to greater activity of the muscle Na(+),K(+)-ATPase pumps. The lower accumulation of potassium in muscle interstitium in the trained leg was associated with delayed fatigue during intense exercise, supporting the hypothesis that interstitial potassium accumulation is involved in the development of fatigue.

Exercise but not prostanoids enhance levels of vascular endothelial growth factor and other proliferative agents in human skeletal muscle interstitium.

In the present study we examined whether exercise and prostanoids have an effect on the muscle interstitial concentration of vascular endothelial growth factor (VEGF) and on the proliferative effect of muscle interstitial fluid. Dialysate from resting and exercising human skeletal muscle, obtained either during control conditions or during cyclooxygenase inhibition, was examined for its content of VEGF and for its effect on endothelial cell proliferation. Microdialysis probes with high (960 kDa) and low (5 kDa) molecular-mass cut-off membranes were placed in the vastus lateralis muscle of healthy young males. The subjects performed one-legged knee extensions (20 W). The concentration of VEGF in the 960 kDa dialysate was greater (P < 0.05) during exercise compared to at rest (67 +/- 28 vs. 230 +/- 22 pg ml-1). The rate of endothelial cell proliferation was 2.7-fold higher (P < 0.05) with the 960 kDa dialysate from resting muscle than with perfusate and was 5.8-fold higher (P < 0.05) than the perfusate value with dialysate from exercising muscle. VEGF was not enhanced with exercise in the 5 kDa dialysate, yet the exercise dialysate induced a 1.9-fold higher (P < 0.05) proliferation than the resting dialysate. Cyclooxygenase inhibition did not affect the VEGF concentration or the proliferating effect of the dialysates (P > 0.05). This study demonstrates for the first time that VEGF is present in the interstitium of human skeletal muscle and that exercise enhances the interstitial concentration of VEGF and of other, as yet unidentified, angiogenic compounds. Products of cyclooxygenase do not appear to have an effect on the release of VEGF or other proliferative agents in human skeletal muscle.

Localization and function of ATP-sensitive potassium channels in human skeletal muscle.

The present study investigated the localization of ATP-sensitive K+ (KATP) channels in human skeletal muscle and the functional importance of these channels for human muscle K+ distribution at rest and during muscle activity. Membrane fractionation based on the giant vesicle technique or the sucrose-gradient technique in combination with Western blotting demonstrated that the KATP channels are mainly located in the sarcolemma. This localization was confirmed by immunohistochemical measurements. With the microdialysis technique, it was demonstrated that local application of the KATP channel inhibitor glibenclamide reduced (P < 0.05) interstitial K+ at rest from approximately 4.5 to 4.0 mM, whereas the concentration in the control leg remained constant. Glibenclamide had no effect on the interstitial K+ accumulation during knee-extensor exercise at a power output of 60 W. In contrast to in vitro conditions, the present study demonstrated that under in vivo conditions the KATP channels are active at rest and contribute to the accumulation of interstitial K+.