Cross-adaptive responses to different forms of leg training: skeletal muscle biochemistry and histochemistry

10-20-30 training increases performance and lowers blood pressure and VEGF in runners

The present study examined the effect of training by the 10-20-30 concept on performance, blood pressure (BP), and skeletal muscle angiogenesis as well as the feasibility of completing high-intensity interval training in local running communities. One hundred sixty recreational runners were divided into either a control group (CON; n = 28), or a 10-20-30 training group (10-20-30; n = 132) replacing two of three weekly training sessions with 10-20-30 training for 8 weeks and performance of a 5-km run (5-K) and BP was measured. VO2max was measured and resting muscle biopsies were taken in a subgroup of runners (n = 18). 10-20-30 improved 5-K time (38 s) and lowered systolic BP (2 ± 1 mmHg). For hypertensive subjects in 10-20-30 (n = 30), systolic and diastolic BP was lowered by 5 ± 4 and 3 ± 2 mmHg, respectively, which was a greater reduction than in the non-hypertensive subjects (n = 102). 10-20-30 increased VO2max but did not influence muscle fiber area, distribution or capillarization, whereas the expression of the pro-angiogenic vascular endothelial growth factor (VEGF) was lowered by 22%. No changes were observed in CON. These results suggest that 10-20-30 training is an effective and easily implemented training intervention improving endurance performance, VO2max and lowering BP in recreational runners, but does not affect muscle morphology and reduces muscle VEGF.

Muscle cellular properties in the ice hockey player: a model for investigating overtraining?

In this study, we hypothesized that athletes involved in 5-6 months of sprint-type training would display higher levels of proteins and processes involved in muscle energy supply and utilization. Tissue was sampled from the vastus lateralis of 13 elite ice hockey players (peak oxygen consumption = 51.8 ± 1.3 mL·kg(-1)·min(-1); mean ± standard error) at the end of a season (POST) and compared with samples from 8 controls (peak oxygen consumption = 45.5 ± 1.4 mL·kg(-1)·min(-1)) (CON). Compared with CON, higher activities were observed in POST (p < 0.05) only for succinic dehydrogenase (3.32 ± 0.16 mol·(mg protein)(-1)·min(-1) vs. 4.10 ± 0.11 mol·(mg protein)(-1)·min(-1)) and hexokinase (0.73 ± 0.05 mol·(mg protein)(-1)·min(-1) vs. 0.90 ± 0.05mol·(mg protein)(-1)·min(-1)) but not for phosphorylase, phosphofructokinase, and creatine phosphokinase. No differences were found in Na(+),K(+)-ATPase concentration (β(max): 262 ± 36 pmol·(g wet weight)(-1) vs. 275 ± 27 pmol·(g wet weight)(-1)) and the maximal activity of the sarcoplasmic reticulum Ca(2+)-ATPase (98.1 ± 6.1 µmol·(g protein)(-1)·min(-1) vs. 102 ± 3.3 µmol·(g protein)(-1)·min(-1)). Cross-sectional area was lower (p < 0.05) in POST but only for the type IIA fibres (6312 ± 684 μm(2) vs. 5512 ± 335 μm(2)), while the number of capillary counts per fibre and the capillary to fibre area ratio were generally higher (p < 0.05). These findings suggest that elite trained ice hockey players display elevations only in support of glucose-based aerobic metabolism that occur in the absence of alterations in excitation-contraction processes.

Cellular responses in skeletal muscle to a season of ice hockey

We hypothesized that a season of ice hockey would result in extensive remodeling of muscle. Tissue sampled from the vastus lateralis of 15 players (age = 20.6 ± 0.4 years; mean ± SE) prior to (PRE) and following (POST) a season was used to characterize specific adaptations. Measurement of representative metabolic pathway enzymes indicated higher maximal activities in POST than in PRE (p < 0.05) for succinic dehydrogenase (3.26 ± 0.31 vs. 3.91 ± 0.11 mol mg protein(-1) min(-1)), citrate synthase (7.26 ± 0.70 vs. 8.70 ± 0.55 mol mg protein(-1) min(-1)), and phosphofructokinase (12.8 ± 1.3 vs. 14.4 ± 0.96 mol mg protein(-1) min(-1)) only. The season resulted in an increase in Na+-K+-ATPase concentration (253 ± 6.3 vs. 265 ± 6.0 pmol g(-1) wet weight), a decrease (p < 0.05) in maximal activity of the sarcoplasmic reticulum Ca2+-ATPase (107 ± 4.2 micromol g protein(-1) min(-1) vs. 92.0 ± 4.6 micromol g protein(-1) min(-1)), and no change in the distribution (%) of fibre types. A smaller (p < 0.05) cross-sectional area (CSA) for both type I (-11.7%) and type IIA (-18.2%) fibres and a higher (p < 0.05) capillary count/CSA for type I (+17.9%) and type IIA (+17.2%) were also found over the season. No changes were found in peak oxygen consumption (51.4 ± 1.2 mL kg(-1) min(-1) vs. 52.3 ± 1.3 mL kg(-1) min(-1)). The results suggest, based on the alterations in oxidative and perfusion potentials and muscle mass, that the dominant adaptations are in support of oxidative metabolism, which occurs at the expense of fibre CSA and possibly force-generating potential.

Effect of high intensity training on capillarization and presence of angiogenic factors in human skeletal muscle

The effect of intense training on endothelial proliferation, capillary growth and distribution of vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) was examined in human skeletal muscle. Two intermittent knee extensor training protocols (at approximately 150% (Study 1) versus approximately 90% (Study 2) of leg (O(2) max)) were conducted. Muscle biopsies were obtained throughout the training periods for immunohistochemical assessment of capillarization, cell proliferation (Ki-67-positive cells), VEGF and bFGF. In Study 1, microdialysis samples were collected from the trained and untrained leg at rest and during exercise and added to endothelial cells to measure the proliferative effect. After 4 weeks of training there was a higher (P < 0.05) capillary-to-fibre ratio (Study 1: 2.4 +/- 0.1 versus 1.7 +/- 0.1) and number of Ki-67-positive cells (Study 1: 0.18 +/- 0.05 versus 0.00 +/- 0.01) than before training. Neither the location of proliferating endothelial cells nor capillarization was related to muscle fibre type. The endothelial cell proliferative effect of the muscle microdialysate increased from rest to exercise in both the untrained leg (from 262 +/- 60 to 573 +/- 87% of control perfusate) and the trained leg (from 303 +/- 75 to 415 +/- 108% of perfusate). VEGF and bFGF were localized in endothelial and skeletal muscle cells and training induced no changes in distribution. The results demonstrate that intense intermittent endurance training induces capillary growth and a transient proliferation of endothelial cells within 4 weeks, with a similar growth occurring around type I versus type II muscle fibres.

Mechanism of enhanced insulin sensitivity in athletes. Increased blood flow, muscle glucose transport protein (GLUT-4) concentration, and glycogen synthase activity

We examined the mechanisms of enhanced insulin sensitivity in 9 male healthy athletes (age, 25 +/- 1 yr; maximal aerobic power [VO2max], 57.6 +/- 1.0 ml/kg per min) as compared with 10 sedentary control subjects (age, 28 +/- 2 yr; VO2max, 44.1 +/- 2.3 ml/kg per min). In the athletes, whole body glucose disposal (240-min insulin clamp) was 32% (P < 0.01) and nonoxidative glucose disposal (indirect calorimetry) was 62% higher (P < 0.01) than in the controls. Muscle glycogen content increased by 39% in the athletes (P < 0.05) but did not change in the controls during insulin clamp. VO2max correlated with whole body (r = 0.60, P < 0.01) and nonoxidative glucose disposal (r = 0.64, P < 0.001). In the athletes forearm blood flow was 64% greater (P < 0.05) than in the controls, whereas their muscle capillary density was normal. Basal blood flow was related to VO2max (r = 0.63, P < 0.05) and glucose disposal during insulin infusion (r = 0.65, P < 0.05). The forearm glucose uptake in the athletes was increased by 3.3-fold (P < 0.01) in the basal state and by 73% (P < 0.05) during insulin infusion. Muscle glucose transport protein (GLUT-4) concentration was 93% greater in the athletes than controls (P < 0.01) and it was related to VO2max (r = 0.61, P < 0.01) and to whole body glucose disposal (r = 0.60, P < 0.01). Muscle glycogen synthase activity was 33% greater in the athletes than in the controls (P < 0.05), and the basal glycogen synthase fractional activity was closely related to blood flow (r = 0.88, P < 0.001).

IN CONCLUSION

(a) athletes are characterized by enhanced muscle blood flow and glucose uptake. (b) The cellular mechanisms of glucose uptake are increased GLUT-4 protein content, glycogen synthase activity, and glucose storage as glycogen. (c) A close correlation between glycogen synthase fractional activity and blood flow suggests that they are causally related in promoting glucose disposal.

Muscular adaptations to exercise and training

This article provides an overview of the characteristics of skeletal muscle, with an emphasis on equine skeletal muscle. A discussion of many of the adaptive processes that can occur in this tissue in response to altered states of physical activity is also included.

The effect of long-term high-frequency stimulation on capillary density and fibre types in rabbit fast muscles

Rabbit fast muscles (tibialis anterior, t.a.; extensor digitorum longus, e.d.l.; and peroneal muscles) were stimulated for up to 28 days by electrodes implanted in the vicinity of the lateral popliteal (peroneal) nerve for 8 h/day, using either intermittent high-frequency (three trains at 40 Hz/min, each 5 s duration), or continuous stimulation at 10 Hz. This did not result in muscle hypertrophy even after 28 days. Capillary density (number of capillaries/mm2) was increased in e.d.l. from 251 +/- 3 to 366 +/- 6 after 14 days of stimulation and from 251 +/- 3 to 514 +/- 13 after 28 days of stimulation at 40 Hz. In t.a., capillary density increased from 373 +/- 5 to 583 +/- 10 after 14 days of stimulation at 40 Hz. The capillary/fibre ratio increased in e.d.l. from 1.25 +/- 0.02 to 1.86 +/- 0.04 at 14 days and to 2.07 +/- 0.06 at 28 days. In t.a., capillary/fibre ratio increased from 1.40 +/- 0.03 to 1.83 +/- 0.05 at 14 days. All these changes were significant (P less than 0.0005). Analysis of capillary density, capillary/fibre ratio, fibre areas and proportion of different fibre types in muscles stimulated for shorter periods showed no changes in capillary density, capillary/fibre ratio or fibre areas in e.d.l. or t.a. stimulated for 4 days; there was a decrease in the proportion of fast glycolytic fibres from 42 to 32% (P less than 0.0025) and increase in fast oxidative from 37.6 to 41.2% in e.d.l. Muscles stimulated for 7 days showed increases in capillary density and capillary/fibre ratio in fast predominantly glycolytic fibres in e.d.l., and a decrease in capillary density in fast and slow oxidative fibres in t.a. This was partly due to the increase in fibre areas in these groups (capillary/fibre ratio in t.a. was not significantly changed). No changes were observed in fibre areas in e.d.l. Stimulation at 10 Hz produced increase in capillary/fibre ratio in the vicinity of glycolytic fibres after only 4 days. High-frequency intermittent stimulation leads to a massive capillary growth which starts first in the muscle with a higher proportion of glycolytic fibres (e.d.l.), has a later onset than continuous low-frequency stimulation, and may be due to a combination of high blood flow and metabolic factors.

Hockey: Optimizing Performance and Safety

In brief: A panel of physiologists, orthopedists, and a physical therapist discuss hockey performance, training, injuries, and equipment. Heart rate monitoring, muscle biopsies, and analyses of the physiological demands of hockey show that training with short work/rest ratios and practicing skills before endurance will optimize performance. Most injuries occur during games vs practice, and the incidence is higher at the beginning of the season due to lack of conditioning and inadequate equipment. Injuries increase again at the end of the season because of the fierce competition for play-off positions.