Physiological Adaptations to Hypoxic vs. Normoxic Training during Intermittent Living High

In the setting of “living high,” it is unclear whether high-intensity interval training (HIIT) should be performed “low” or “high” to stimulate muscular and performance adaptations. Therefore, 10 physically active males participated in a 5-week “live high-train low or high” program (TR), whilst eight subjects were not engaged in any altitude or training intervention (CON). Five days per week (~15.5 h per day), TR was exposed to normobaric hypoxia simulating progressively increasing altitude of ~2,000–3,250 m. Three times per week, TR performed HIIT, administered as unilateral knee-extension training, with one leg in normobaric hypoxia (~4,300 m; TR_HYP) and with the other leg in normoxia (TR_NOR). “Living high” elicited a consistent elevation in serum erythropoietin concentrations which adequately predicted the increase in hemoglobin mass (r = 0.78, P < 0.05; TR: +2.6%, P < 0.05; CON: −0.7%, P > 0.05). Muscle oxygenation during training was lower in TR_HYP vs. TR_NOR (P < 0.05). Muscle homogenate buffering capacity and pH-regulating protein abundance were similar between pretest and posttest. Oscillations in muscle blood volume during repeated sprints, as estimated by oscillations in NIRS-derived tHb, increased from pretest to posttest in TR_HYP (~80%, P < 0.01) but not in TR_NOR (~50%, P = 0.08). Muscle capillarity (~15%) as well as repeated-sprint ability (~8%) and 3-min maximal performance (~10–15%) increased similarly in both legs (P < 0.05). Maximal isometric strength increased in TR_HYP (~8%, P < 0.05) but not in TR_NOR (~4%, P > 0.05). In conclusion, muscular and performance adaptations were largely similar following normoxic vs. hypoxic HIIT. However, hypoxic HIIT stimulated adaptations in isometric strength and muscle perfusion during intermittent sprinting.

Reliability of power output during eccentric sprint cycling

The purpose of this study was to determine the reliability of power outputs during maximal intensity eccentric cycling over short durations (i.e., eccentric sprint cycling) on a "motor-driven" isokinetic ergometer. Fourteen physically active male subjects performed isokinetic eccentric cycling sprints at 40, 60, 80, 100, and 120 revolutions per minute (rpm) on 4 separate occasions (T1-T4). Each sprint lasted for 6 seconds, and absolute measures of mean power (MP) and peak power (PP) per revolution were recorded. Significant increases in MP and PP were observed between T1 and subsequent trials, but no significant differences were identified between T2, T3, and T4. The coefficient of variation (CV) and intraclass correlation coefficient (ICC) were calculated to reflect within-subject and between-session reliability of MP and PP at each cadence. The CV improved to below 10% for cadences of 60, 80, 100, and 120 rpm between T3 and T4, and the majority of ICC values improved to above 0.90. The remaining ICC values remained in the moderate range between T3 and T4 (i.e., 0.82-0.89). Coefficient of variation and ICC values for the 40 rpm cadence remained at unacceptable levels throughout the 4 trials and thus should be avoided in future investigations. The results of this study indicate that reliable power outputs may be obtained after 2 familiarization sessions during eccentric sprint cycling at cadences ranging from 60 to 120 rpm.

Covariance of Isometric and Dynamic Arm Contractions: Multivariate Genetic Analysis

The purpose of the present study was to examine genetic and environmental contributions to individual differences in maximal isometric, concentric and eccentric muscle strength and muscle cross-sectional area (MCSA) of the elbow flexors. A generality versus specificity hypothesis was explored to test whether the 4 strength variables share a genetic component or common factors in the environment or whether the genetic/environmental factors are specific for each strength variable. The 4 variables under study were measured in 25 monozygotic and 16 dizygotic male Caucasian twin pairs (22.4 ± 3.7 years). The multivariate genetic analyses showed that all 4 variables shared a genetic and environmental component, which accounted for 43% and 6% in MCSA (h2= 81%), 47% and 20% in eccentric (h2= 65%), 58% and 4% in isometric (h2= 70%) and 32% and 1% in concentric strength (h2= 32%) respectively. The remaining variation was accounted for by contraction type specific and muscle cross-sectional area specific genetic and environmental effects, which accounted for 38% and 14% in MCSA, 18% and 15% in eccentric, 12% and 26% in isometric and 0% and 67% in concentric strength respectively. This exploratory multivariate study suggests shared pleiotropic gene action for MCSA, eccentric, isometric and concentric strength, with a moderate to high genetic contribution to the variability of these characteristics.

Protective role of alpha-actinin-3 in the response to an acute eccentric exercise bout

The ACTN3 gene encodes for the alpha-actinin-3 protein, which has an important structural function in the Z line of the sarcomere in fast muscle fibers. A premature stop codon (R577X) polymorphism in the ACTN3 gene causes a complete loss of the protein in XX homozygotes. This study investigates a possible role for the alpha-actinin-3 protein in protecting the fast fiber from eccentric damage and studies repair mechanisms after a single eccentric exercise bout. Nineteen healthy young men (10 XX, 9 RR) performed 4 series of 20 maximal eccentric knee extensions with both legs. Blood (creatine kinase; CK) and muscle biopsy samples were taken to study differential expression of several anabolic (MyoD1, myogenin, MRF4, Myf5, IGF-1), catabolic (myostatin, MAFbx, and MURF-1), and contraction-induced muscle damage marker genes [cysteine- and glycine-rich protein 3 (CSRP3), CARP, HSP70, and IL-6] as well as a calcineurin signaling pathway marker (RCAN1). Baseline mRNA content of CSRP3 and MyoD1 was 49 + or - 12 and 67 + or - 25% higher in the XX compared with the RR group (P = 0.01-0.045). However, satellite cell number was not different between XX and RR individuals. After eccentric exercise, XX individuals tended to have higher serum CK activity (P = 0.10) and had higher pain scores than RR individuals. However, CSRP3 (P = 0.058) and MyoD1 (P = 0.08) mRNA expression tended to be higher after training in RR individuals compared with XX alpha-actinin-3-deficient subjects. This study suggests a protective role of alpha-actinin-3 protein in muscle damage after eccentric training and an improved stress-sensor signaling, although effects are small.

ACTN3 (R577X) genotype is associated with fiber type distribution

α-Actinin-3 is a Z-disc structural protein found only in type II muscle fibers. The X allele of the R577X polymorphism in the ACTN3 gene results in a premature stop codon and α-actinin-3 deficiency in XX homozygotes. Associations between the R577X polymorphism and the muscle-power performance of elite athletes have been described earlier. About 45% of the fiber type proportions are determined by genetic factors. The ACTN3 variant could be one of the contributing genes in the heritability of fiber type distribution through its interaction with calcineurin. The aim of this study was to quantify the association between the polymorphism and muscle fiber type distribution and fast-velocity knee extension strength. Ninety healthy young men (18–29 y) were genotyped for ACTN3 R577X. Knee extensor strength was measured isometrically (45°) and at different dynamic velocities (100–300°/s) on a programmable dynamometer. Twenty-two XX and twenty-two RR subjects underwent a biopsy of the right vastus lateralis muscle. Fiber type composition was determined by immunohistochemistry. Homozygotes for the R allele show significantly higher relative dynamic quadriceps torques at 300°/s, compared with XX carriers ( P < 0.05). Fiber type characteristics differed significantly between the two genotype groups. The percentage surface and number of type IIx fibers were greater in the RR than the XX genotype group ( P < 0.05), and α-actinin-3 protein content is systematically higher in type IIx compared with type IIa fibers (staining intensity ratio IIx to IIa = 1.17). This study shows that the mechanism, by which the ACTN3 polymorphism has its effect on muscle power, might rely on a control function of fiber type proportions.

Effects of creatine supplementation and exercise training on fitness in men 55-75 yr old

effect of oral creatine supplementation (CR; 5 g/day) in conjunction with exercise training on physical fitness was investigated in men between 55 and 75 yr of age (n = 46). A double-blind randomized placebo-controlled (PL) trial was performed over a 6-mo period. Furthermore, a subgroup (n = 20) completed a 1-yr follow-up. The training program consisted of cardiorespiratory endurance training as well as moderate resistance training (2-3 sessions/wk). Endurance capacity was evaluated during a maximal incremental bicycle ergometer test, maximal isometric strength of the knee-extensor muscles was assessed by an isokinetic dynamometer, and body composition was assessed by hydrostatic weighing. Furthermore, in a subgroup (PL: n = 13; CR: n = 12) biopsies were taken from m. vastus lateralis to determine total creatine (TCr) content. In PL, 6 mo of training increased peak oxygen uptake rate (+16%; P < 0.05). Fat-free mass slightly increased (+0.3 kg; P < 0.05), whereas percent body fat slightly decreased (-1.2%; P < 0.05). The training intervention did not significantly change either maximal isometric strength or body weight. The responses were independent of CR. Still, compared with PL, TCr was increased by approximately 5% in CR, and this increase was closely correlated with initial muscle creatine content (r = -0.78; P < 0.05). After a 1-yr follow-up, muscle TCr was not higher in CR than in PL. Furthermore, the other measurements were not affected by CR. It is concluded that long-term creatine intake (5 g/day) in conjunction with exercise training does not beneficially impact physical fitness in men between 55 and 75 yr of age.

Hand strength and fatigue in patients with hereditary motor and sensory neuropathy (types I and II)

OBJECTIVES

To compare maximal isometric hand strength and fatigue between subjects with hereditary motor and sensory neuropathy (HMSN) and healthy controls and to test the reproducibility of handgrip strength (peak force of handgrip [PFgrip]) and fatigue.

DESIGN

PFgrip and the decline in PFgrip during 3 sets of 15 contractions were compared.

SETTING

University hospital in The Netherlands.

PARTICIPANTS

Twenty subjects with HMSN and 20 age- and sex-matched healthy controls; 15 healthy subjects for the reproducibility part of the study.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

PFgrip and the decline in PFgrip were compared by using a digital handgrip dynamometer. Two-point and lateral pinch measurements of subjects with HMSN were standardized against reference values. Reproducibility measurements were performed on 15 healthy subjects on 2 separate occasions within a 1-week interval.

RESULTS

PFgrip was significantly lower in the HMSN subjects compared with controls (P<.05). Pinch measurements also showed a large variance from average normal performance. No significant difference was found in the decline in percentage of PFgrip. Reproducibility was excellent for PFgrip (intraclass correlation coefficient [ICC]=.98; 95% confidence interval [CI],.95-.99) but poor for fatigue (ICC=.62; 95% CI,.20-.85).

CONCLUSION

PFgrip and 2-point and lateral pinch in HMSN subjects were significantly reduced compared with healthy controls. Our findings indicated that the rate of decline of PFgrip during effort does not vary between groups.

Resistance training alters torque-velocity relation of elbow flexors in elderly men

PURPOSE

The aim of the study was to compare in vivo dynamic muscle characteristics (torque-velocity relation and maximal contraction velocity) of sedentary young subjects with elderly men before and after training.

METHODS

Elbow flexion maximal isometric (Tmax) and dynamic torque at velocities between 100 degrees.s-1 and 600 degrees.s-1 were measured, from which maximal contraction velocity was estimated (eVmax). These parameters were obtained from 18 young sedentary subjects (Y) and from 23 healthy sedentary elderly (mean age 63 yr) men (E) before (PRE), after 13 wk (MID), and 26 wk (POST) of moderate intensity resistance training (30RM) of the elbow flexor muscles.

RESULTS

Y and E before training had similar Tmax, but mean dynamic torque over all velocities was 49.1% higher in Y compared with E. After 13 wk of training TmaxE increased by 8.2% and mean dynamic torque increased by 61.2%, with a velocity dependent gain. For eVmaxE an increase of 21.8% was observed. The second 13-wk training period did not induce further increases.

CONCLUSION

The results of the present study demonstrate that, after moderate intensity resistance training of healthy elderly men, maximal contraction velocity of elbow flexors (eVmax), estimated from the torque-velocity curve, increased to values observed for sedentary young men.