Passive mechanical properties of adipose tissue and skeletal muscle from C57BL/6J mice.

Skeletal muscle and adipose tissue are characterized by unique structural features finely tuned to meet specific functional demands. In this study, we investigated the passive mechanical properties of soleus (SOL), extensor digitorum longus (EDL) and diaphragm (DIA) muscles, as well as subcutaneous (SAT), visceral (VAT) and brown (BAT) adipose tissues from 13 C57BL/6J mice. Thereto, alongside stress-relaxation assessments we subjected isolated muscles and adipose tissues (ATs) to force-extension tests up to 10% and 30% of their optimal length, respectively. Peak passive stress was highest in the DIA, followed by the SOL and lowest in the EDL (p < 0.05). SOL displayed also the highest Young's modulus and hysteresis among muscles (p < 0.05). BAT demonstrated highest peak passive stress and Young's modulus followed by VAT (p < 0.05), while SAT showed the highest hysteresis (p < 0.05). When comparing data across all six biological specimens at fixed passive force intervals (i.e., 20-40 and 50-70 mN), skeletal muscles exhibited significantly higher peak stresses and strains than ATs (p < 0.05). Young's modulus was higher in skeletal muscles than in ATs (p < 0.05). Muscle specimens exhibited slower force relaxation in the first phase compared to ATs (p < 0.05), while there was no significant difference in behavior between muscles and AT in the second phase of relaxation. The study revealed distinctive mechanical behaviors specific to different tissues, and even between different muscles and ATs. These variations in mechanical properties are likely such to optimize the specific functions performed by each biological tissue.

Acute resveratrol supplementation in coronary artery disease: towards patient stratification.

Objective: Resveratrol (RV) is a polyphenol with antioxidant, anti-inflammatory and cardio-protective properties. Our objective was to investigate whether acute supplementation with high doses of RV would improve flow-mediated dilation (FMD) and oxygen consumption (VO2) kinetics in older coronary artery disease (CAD) patients. Design: We employed a placebo-controlled, single-blind, crossover design in which ten participants (aged 66.6 ± 7.8 years) received either RV or placebo (330 mg, 3× day-1) during three consecutive days plus additional 330 mg in the morning of the fourth day with a seven-day wash-out period in-between. On the fourth day, FMD of the brachial artery and VO2 on-kinetics were determined. Results: RV improved FMD in patients who had undergone coronary artery bypass grafting (CABG; -1.4 vs. 5.0%; p = .004), but not in those who had undergone percutaneous coronary intervention (PCI; 4.2 vs. -0.2%; NS). Conclusion: Acute high dose supplementation with RV improved FMD in patients after CABG surgery but impaired FMD in patients who underwent PCI. The revascularization method-related differential effects of RV may be due to its direct effects on endothelial-dependent dilator responses. Our findings have important implications for personalized treatment and stratification of older CAD patients.

Morphological alterations of mouse skeletal muscles during early ageing are muscle specific.

One of the hallmarks of ageing is muscle wasting that may be preceded by morphological changes, such as capillary rarefaction. Muscle-specific changes in morphology in early ageing may differ between locomotor and respiratory muscles. To investigate this, we compared capillarization, fiber type composition, fiber cross-sectional area (FCSA) and oxidative capacity of individual fibers of the soleus (n = 6/5 for 20- and 79 weeks, respectively), extensor digitorum longus (EDL: n = 3/3) and diaphragm (n = 7/5) muscles in 20- (mature) and 79-week-old (early ageing) CD-1 female mice. There was no significant loss of soleus and EDL mass. The FCSA was larger and the capillary density lower at 79 than 20 weeks in the diaphragm, while in the EDL the opposite was found (both p ≤ 0.002) with no significant ageing-related differences in the soleus. The heterogeneity in capillary spacing, which may negatively impact on muscle oxygenation, was highest in muscles from 20-week-old mice, irrespective of muscle (p ≤ 0.011). Succinate dehydrogenase activity, indicative of oxidative capacity, and capillary to fiber ratio did not significantly change with age in any muscle. At all ages, the capillary supply to a fiber was positively related to FCSA in each muscle. We conclude that despite previously reported early age-related reductions in specific tension in both locomotor and respiratory muscles, morphological changes show a muscle-specific pattern in early ageing CD-1 mice. Specifically, early ageing was associated with 1) diaphragm hypertrophy 2) and fiber atrophy in the EDL that was not accompanied by angiogenesis, capillary rarefaction or reductions in oxidative capacity.

Long-Term Endurance and Power Training May Facilitate Motor Unit Size Expansion to Compensate for Declining Motor Unit Numbers in Older Age.

The evidence concerning the effects of exercise in older age on motor unit (MU) numbers, muscle fiber denervation and reinnervation cycles is inconclusive and it remains unknown whether any effects are dependent on the type of exercise undertaken or are localized to highly used muscles. MU characteristics of the vastus lateralis (VL) were assessed using surface and intramuscular electromyography in eighty-five participants, divided into sub groups based on age (young, old) and athletic discipline (control, endurance, power). In a separate study of the biceps brachii (BB), the same characteristics were compared in the favored and non-favored arms in eleven masters tennis players. Muscle size was assessed using MRI and ultrasound. In the VL, the CSA was greater in young compared to old, and power athletes had the largest CSA within their age groups. Motor unit potential (MUP) size was larger in all old compared to young (p < 0.001), with interaction contrasts showing this age-related difference was greater for endurance and power athletes than controls, and MUP size was greater in old athletes compared to old controls. In the BB, thickness did not differ between favored and non-favored arms (p = 0.575), but MUP size was larger in the favored arm (p < 0.001). Long-term athletic training does not prevent age-related loss of muscle size in the VL or BB, regardless of athletic discipline, but may facilitate more successful axonal sprouting and reinnervation of denervated fibers. These effects may be localized to muscles most involved in the exercise.

Hip and spine bone mineral density are greater in master sprinters, but not endurance runners compared with non-athletic controls.

We examined bone density in older athletes and controls. Sprinters had greater hip and spine bone density than endurance athletes and controls, whereas values were similar in the latter two groups. These results could not be explained by differences in impact, muscle size or power between sprint and endurance athletes. PURPOSE: We examined the relationship between prolonged participation in regular sprint or endurance running and skeletal health at key clinical sites in older age, and the factors responsible for any associations which we observed. METHODS: We recruited 38 master sprint runners (28 males, 10 females, mean age 71 ± 7 years), 149 master endurance runners (111 males, 38 females, mean age 70 ± 6 years) and 59 non-athletic controls (29 males, 30 females, mean age 74 ± 5 years). Dual X-ray absorptiometry was used to assess hip and spine bone mineral density (BMD), body composition (lean and fat mass), whilst jump power was assessed with jumping mechanography. In athletes, vertical impacts were recorded over 7 days from a waist-worn accelerometer, and details of starting age, age-graded performance and training hours were recorded. RESULTS: In ANOVA models adjusted for sex, age, height, body composition, and jump power, sprinter hip BMD was 10 and 14% greater than that of endurance runners and controls respectively. Sprinter spine BMD was also greater than that of both endurance runners and controls. There were no differences in hip or spine BMD between endurance runners and controls. Stepwise regression showed only discipline (sprint/endurance), sex, and age as predictors of athlete spine BMD, whilst these variables and starting age were predictive of hip BMD. CONCLUSIONS: Regular running is associated with greater BMD at the fracture-prone hip and spine sites in master sprinters but not endurance runners. These benefits cannot be explained by indicators of mechanical loading measured in this study including vertical impacts, body composition or muscular output.

The strength of weight-bearing bones is similar in amenorrheic and eumenorrheic elite long-distance runners.

Regular intense endurance exercise can lead to amenorrhea with possible adverse consequences for bone health. We compared whole body and regional bone strength and skeletal muscle characteristics between amenorrheic (AA: n = 14) and eumenorrheic (EA: n = 15) elite adult female long-distance runners and nonathletic controls (C: n = 15). Participants completed 3-day food diaries, dual-energy X-ray absorptiometry (DXA), magnetic resonance imaging (MRI), peripheral quantitative computed tomography (pQCT), and isometric maximal voluntary knee extension contraction (MVC). Both athlete groups had a higher caloric intake than controls, with no significant difference between athlete groups. DXA revealed lower bone mineral density (BMD) at the trunk, rib, pelvis, and lumbar spine in the AA than EA and C. pQCT showed greater bone size in the radius and tibia in EA and AA than C. The radius and tibia of AA had a larger endocortical circumference than C. Tibia bone mass and moments of inertia (Ix and Iy) were greater in AA and EA than C, whereas in the radius, only the proximal Iy was larger in EA than C. Knee extensor MVC did not differ significantly between groups. Amenorrheic adult female elite long-distance runners had lower BMD in the trunk, lumbar spine, ribs, and pelvis than eumenorrheic athletes and controls. The radius and tibia bone size and strength indicators were similar in amenorrheic and eumenorrheic athletes, suggesting that long bones of the limbs differ in their response to amenorrhea from bones in the trunk.

Absence of Bilateral Differences in Child Baseball Players with Throwing-related Pain.

The aim of this study was to assess whether side-to-side differences in morphology and function of the upper limbs in 11-12 year-old male baseball players with throwing-related pain (n=14) were more pronounced than that of age-matched healthy untrained subjects (n=16). Baseball players 1) had played baseball≥4.5 h·wk-1 for ≥ 4 years and (2) suffered from moderate-intensity (3-6 points on 10-point questionnaire scale) throwing-related pain in the shoulder or elbow in at least 2 training sessions within the past month. The range of motion (ROM), function and structure of the elbows and shoulders were assessed using goniometry, isokinetic dynamometry and ultrasonography. While the ROM and eccentric external peak torque of internal shoulder rotation were lower, the thickness of the supraspinatus tendon, the ulnar collateral ligament and articular cartilage of the humeral head were larger in baseball players than controls. There were, however, no significant side-to-side differences in any parameter in either group. In conclusion, it is unlikely that side-to-side differences in shoulder and upper limb structure and function contributed to the throwing-related pain in young baseball players, but low shoulder eccentric external peak torque and range of internal rotation may predispose to throwing-related pain.

ACE inhibition modifies exercise-induced pro-angiogenic and mitochondrial gene transcript expression.

Skeletal muscle responds to endurance exercise with an improvement of biochemical pathways that support substrate supply and oxygen-dependent metabolism. This is reflected by enhanced expression of associated factors after exercise and is specifically modulated by tissue perfusion and oxygenation. We hypothesized that transcript expression of pro-angiogenic factors (VEGF, tenascin-C, Angpt1, Angpt1R) and oxygen metabolism (COX4I1, COX4I2, HIF-1α) in human muscle after an endurance stimulus depends on vasoconstriction, and would be modulated through angiotensin-converting enzyme inhibition by intake of lisinopril. Fourteen non-specifically trained, male Caucasians subjects, carried out a single bout of standardized one-legged bicycle exercise. Seven of the participants consumed lisinopril in the 3 days before exercise. Biopsies were collected pre- and 3 h post-exercise from the m. vastus lateralis. COX4I1 (P = 0.03), COX4I2 (P = 0.04) mRNA and HIF-1α (P = 0.05) mRNA and protein levels (P = 0.01) showed an exercise-induced increase in the group not consuming the ACE inhibitor. Conversely, there was a specific exercise-induced increase in VEGF transcript (P = 0.04) and protein levels (P = 0.03) and a trend for increased tenascin-c transcript levels (P = 0.09) for subjects consuming lisinopril. The observations indicate that exercise-induced expression of transcripts involved in angiogenesis and mitochondrial energy metabolism are to some extent regulated via a hypoxia-related ACE-dependent mechanism.

Single muscle fibre contractile properties differ between body-builders, power athletes and control subjects.

NEW FINDINGS: What is the central question of this study? Do the contractile properties of single muscle fibres differ between body-builders, power athletes and control subjects? What is the main finding and its importance? Peak power normalized for muscle fibre volume in power athletes is higher than in control subjects. Compared with control subjects, maximal isometric tension (normalized for muscle fibre cross-sectional area) is lower in body-builders. Although this difference may be caused in part by an apparent negative effect of hypertrophy, these results indicate that the training history of power athletes may increase muscle fibre quality, whereas body-building may be detrimental. We compared muscle fibre contractile properties of biopsies taken from the vastus lateralis of 12 body-builders (BBs; low- to moderate-intensity high-volume resistance training), six power athletes (PAs; high-intensity, low-volume combined with aerobic training) and 14 control subjects (Cs). Maximal isotonic contractions were performed in single muscle fibres, typed with SDS-PAGE. Fibre cross-sectional area was 67 and 88% (P < 0.01) larger in BBs than in PAs and Cs, respectively, with no significant difference in fibre cross-sectional area between PAs and Cs. Fibres of BBs and PAs developed a higher maximal isometric tension (32 and 50%, respectively, P < 0.01) than those of Cs. The specific tension of BB fibres was 62 and 41% lower than that of PA and C fibres (P < 0.05), respectively. Irrespective of fibre type, the peak power (PP) of PA fibres was 58% higher than that of BB fibres (P < 0.05), whereas BB fibres, despite considerable hypertrophy, had similar PP to the C fibres. This work suggests that high-intensity, low-volume resistance training with aerobic exercise improves PP, while low- to moderate-intensity high-volume resistance training does not affect PP and results in a reduction in specific tension. We postulate that the decrease in specific tension is caused by differences in myofibrillar density and/or post-translational modifications of contractile proteins.

Whey protein plus bicarbonate supplement has little effects on structural atrophy and proteolysis marker immunopatterns in skeletal muscle disuse during 21 days of bed rest.

OBJECTIVES: To investigate the effect of whey protein plus potassium bicarbonate supplement on disused skeletal muscle structure and proteolysis after bed rest (BR). METHODS: Soleus (SOL) and vastus lateralis (VL) biopsies were sampled from ten (n=10) healthy male subjects (aged 31±6 years) who did BR once with and once without protein supplement as a dietary countermeasure (cross-over study design). The structural changes (myofibre size and type distribution) were analysed by histological sections, and muscle protein breakdown indirectly via the proteolysis markers, calpain 1 and 3, calpastatin, MuRF1 and 2, both in muscle homogenates and by immunohistochemistry. RESULTS: BR caused size-changes in myofiber cross-sectional area (FCSA, SOL, p=0,004; VL, p=0.03), and myofiber slow-to-fast type transition with increased hybrids (SOL, p=0.043; VL, p=0.037) however with campaign differences in SOL (p<0.033). No significant effect of BR and supplement was found by any of the key proteolysis markers. CONCLUSIONS: Campaign differences in structural muscle adaptation may be an issue in cross-over design BR studies. The whey protein plus potassium bicarbonate supplement did not attenuate atrophy and fibre type transition during medium term bed rest. Alkaline whey protein supplements may however be beneficial as adjuncts to exercise countermeasures in disuse.

Impact of age, performance and athletic event on injury rates in master athletics - first results from an ongoing prospective study.

OBJECTIVES: Recent studies have identified rates of injuries in young elite athletes during major athletic events. However, no such data exist on master athletes. The aim of this study was to assess incidence and types of injuries during the 2012 European Veteran Athletics Championships as a function of age, performance and athletic discipline. METHODS: Report forms were used to identify injured athletes and injury types. Analysis included age (grouped in five-year bands beginning at age 35 years), athletic event, and age-graded performance. RESULTS: Of the 3154 athletes (53.2 years (SD 12.3)) that participated in the championships (1004 (31.8%) women, 2150 (68.2%) men), 76 were registered as injured; 2.8% of the female (29), 2.2% of the male (47) athletes. There were no fractures. One injury required operative treatment (Achilles tendon rupture). Injury rates were significantly higher in the sprint/middle distance/jumps than the throws, long distance and decathlon/heptathlon groups (X(2) (3)=16.187, P=0.001). There was no significant interrelationship with age (X(2) (12)=6.495, P=0.889) or age-graded performance (X(2) (3)=3.563, P=0.313). CONCLUSIONS: The results suggest that healthy master athletes have a low risk of injury that does not increase with age or performance.

Effects of age and starting age upon side asymmetry in the arms of veteran tennis players: a cross-sectional study.

UNLABELLED: While tennis playing results in large bone strength benefits in the racquet arm of young players, the effects of tennis playing in old players have not been investigated. Large side asymmetries in bone strength were found in veteran players, which were more pronounced in men, younger players and childhood starters. INTRODUCTION: Regular tennis results in large racquet arm bone and muscle strength advantages; however, these effects have not been studied in old players. The non-racquet arm can act as an internal control for the exercising racquet arm without confounding factors, e.g. genotype. Therefore, veteran tennis player side asymmetries were examined to investigate age, sex and starting age effects on bone exercise benefits. METHODS: Peripheral quantitative computed tomography (pQCT) scans were taken at the radius, ulna and humerus mid-shaft and distal radius in both arms of 88 tennis players (51 males, 37 females; mean age 63.8 ± 11.8 years). Thirty-two players began playing in adulthood, thereby termed 'old starters'; players were otherwise termed 'young starters'. RESULTS: Muscle size and bone strength were greater in the racquet arm; notably, distal radius bone mineral content (BMC) was 13 ± 10% higher and humeral bone area 23 ± 12% larger (both P < 0.001). Epiphyseal BMC asymmetry was not affected by age (P = 0.863) or sex (P = 0.954), but diaphyseal asymmetries were less pronounced in older players and women, particularly in the humerus where BMC, area and moment of resistance asymmetries were 28-34 % less in women (P < 0.01). Bone area and periosteal circumference asymmetries were smaller in old starters (all P < 0.01); most notably, no distal radius asymmetry was found in this group (0.4 ± 3.4%). CONCLUSIONS: Tennis participation is associated with large side asymmetries in muscle and bone strength in old age. Larger relative side asymmetries in men, younger players and young starters suggest a greater potential for exercise benefits to bone in these groups.

Thigh muscle volume in relation to age, sex and femur volume.

Secular changes and intra-individual differences in body shape and size can confound cross-sectional studies of muscle ageing. Normalising muscle mass to height squared is often suggested as a solution for this. We hypothesised that normalisation of muscle volume to femur volume may be a better way of determining the extent of muscle lost with ageing (sarcopenia). Thigh and femur muscle volumes were measured from serial magnetic resonance imaging sections in 20 recreationally active young men (mean age 22.4 years), 25 older men (72.3 years), 18 young women (22.1 years) and 28 older women (72.0 years). There were no age-related differences in femur volume. The relationship between thigh muscle volume and femur volume (R (2) = 0.76; exponent of 1.12; P < 0.01) was stronger than that with height (R (2) = 0.49; exponent of 3.86; P < 0.01) in young participants. For young subjects, the mean muscle/bone ratios were 16.0 and 14.6 for men and women, respectively. For older men and women, the mean ratios were 11.6 and 11.5, respectively. The Z score for the thigh muscle/bone volume ratio relative to young subjects was -2.2 ± 0.7 for older men and -1.4 ± 0.8 for older women. The extent of sarcopenia judged by the muscle/bone ratio was approximately twice that determined when normalising to height squared. These data suggest that the muscle/bone ratio captures the intra-individual loss of muscle mass during ageing, and that the age-related loss of muscle mass may be underestimated when normalised to height squared. The quadriceps seems relatively more affected by ageing than other thigh muscles.

The individual and combined influence of ACE and ACTN3 genotypes on muscle phenotypes before and after strength training.

Alternative measures of muscle size, strength, and power to those used in previous studies could help resolve the controversy surrounding associations between polymorphisms of the angiotensin-I converting enzyme (ACE) and α-actinin-3 (ACTN3) genes and skeletal muscle phenotypes, and the responses to resistance training (RT). To this end, we measured quadriceps femoris muscle volume (Vm), physiological cross-sectional area (PCSA), maximum isometric force (Ft), specific force (Ft per unit PCSA), maximum isoinertial strength (1-RM), and maximum power (Wmax ; n = 40) before and after 9-week knee extension RT in 51 previously untrained young men, who were genotyped for the ACE I/D and ACTN3 R577X polymorphisms. ACTN3 R-allele carriers had greater Vm, 1-RM, and Wmax than XX homozygotes at baseline (all P < 0.05), but responses to RT were independent of ACTN3 genotype (all P > 0.05). Muscle phenotypes were independent of ACE genotype before (all P > 0.05) and after RT (all P > 0.01). However, people with the "optimal" ACE+ACTN3 genotype combination had greater baseline 1-RM and Wmax compared to those with the "suboptimal" profile (both P < 0.0125). We show for the first time that the ACTN3 R577X polymorphism is associated with human Vm and (independently and in combination with the ACE I/D polymorphism) influences 1-RM and Wmax.

Comparison of MRI and DXA to measure muscle size and age-related atrophy in thigh muscles.

OBJECTIVES: Magnetic resonance imaging (MRI) and dual-energy x-ray absorptiometry (DXA) were used to examine the thigh lean mass in young and old men and women. METHODS: A whole-body DXA scan was used to estimate thigh lean mass in young (20 men; 22.4±3.1y; 18 women; 22.1±2.0y) and older adults (25 men; 72.3±4.9y; 28 women; 72.0±4.5y). Thigh lean mass determined with a thigh scan on the DXA or full thigh MRI scans were compared. RESULTS: Although the thigh lean mass quantified by DXA and MRI in young and older participants were correlated (R(2)=0.88; p<0.001) the magnitude of the differences in thigh lean mass between young and old was smaller with DXA than MRI (old vs. young men 79.5±13.1% and 73.4±11.2%; old vs. young women 88.6±11.8% and 79.4±12.3%, respectively). Detailed analysis of MRI revealed 30% smaller quadriceps muscles in the older than young individuals, while the other thigh muscles were only 18% smaller. CONCLUSIONS: DXA underestimates the age-related loss of thigh muscle mass in comparison to MRI. The quadriceps muscles were more susceptible to age-related atrophy compared with other thigh muscles.

Diffusion capacity of the lung in young and old endurance athletes.

Lung diffusion capacity (D LCO) declines with age. A significant proportion of older endurance athletes develop exercise-induced hypoxemia (SaO2<95%). We hypothesised that master endurance athletes have a lower D LCO than age-matched non-athletes. We recruited 33 control (16 young; 17 old) and 29 male endurance athletes (13 young; 16 old) during the World Masters Athletics Indoor Championships, 2012 (Jyväskylä, Finland). To measure D LCO the participant exhaled to residual volume and then quickly inhaled to ≥ 90% total lung capacity from a gas source with 0.3% carbon monoxide. The D LCO and transfer coefficient (K CO) were corrected for the actual haemoglobin concentration. Spirometric function was similar in athletes and age-matched controls. D LCO and K CO were 33% and 25% lower in old and young controls, respectively (P<0.001). Although predicted D LCO and K CO were 11%-points higher in athletes than age-matched controls (P<0.001), they were 23% and 16% lower in old athletes than young controls, respectively (P<0.001). D LCO did not correlate with age-graded performance or weekly training hours. The better lung diffusion capacity in male endurance athletes than age-matched controls might be an adaptation to training, self-selection and/or attrition bias. However, the diffusion capacity of the older athlete is lower than that of the young non-athlete.

Impact of nutrition on muscle mass, strength, and performance in older adults.

Muscle strength plays an important role in determining risk for falls, which result in fractures and other injuries. While bone loss has long been recognized as an inevitable consequence of aging, sarcopenia-the gradual loss of skeletal muscle mass and strength that occurs with advancing age-has recently received increased attention. A review of the literature was undertaken to identify nutritional factors that contribute to loss of muscle mass. The role of protein, acid-base balance, vitamin D/calcium, and other minor nutrients like B vitamins was reviewed. Muscle wasting is a multifactorial process involving intrinsic and extrinsic alterations. A loss of fast twitch fibers, glycation of proteins, and insulin resistance may play an important role in the loss of muscle strength and development of sarcopenia. Protein intake plays an integral part in muscle health and an intake of 1.0-1.2 g/kg of body weight per day is probably optimal for older adults. There is a moderate [corrected] relationship between vitamin D status and muscle strength. Chronic ingestion of acid-producing diets appears to have a negative impact on muscle performance, and decreases in vitamin B12 and folic acid intake may also impair muscle function through their action on homocysteine. An adequate nutritional intake and an optimal dietary acid-base balance are important elements of any strategy to preserve muscle mass and strength during aging.

Is the myonuclear domain size fixed?

It has been suggested that the number of myonuclei in a muscle fibre changes in proportion to the change in fibre size, resulting in a constant myonuclear domain size, defined as the cytoplasmic volume per myonucleus. The myonuclear domain size varies, however, between fibre types and is inversely related with the oxidative capacity of a fibre. Overall, the observations of an increase in myonuclear domain size during both maturational growth and overload-induced hypertrophy, and the decrease in myonuclear domain size during disuse- and ageing-associated muscle atrophy suggest that the concept of a constant myonuclear domain size needs to be treated cautiously. It also suggests that only when the myonuclear domain size exceeds a certain threshold during growth or overload-induced hypertrophy acquisition of new myonuclei is required for further fibre hypertrophy.

Side-to-side differences in bone strength in master jumpers and sprinters.

INTRODUCTION: This study evaluated side-to-side difference in tibial bone structure, calf muscle cross-sectional area (CSA) and hopping force in master athletes as a result of training for sports with different magnitudes of inter-leg loading difference. METHODS: Tibial bone parameters (at 4%, 14%, 38% and 66% tibial length proximal to distal end), muscle CSA (at 66% tibial length) and hopping forces of both legs of 51 master athletes (conditioned jumpers, conditioned triple jumpers, unconditioned jumpers, hurdlers and sprinters) were examined using pQCT. In epiphyseal 4% slice bone CSA (Ar.tot), total BMC (vBMC.tot), trabecular BMC (vBMC.tb) cortical BMC (vBMC.ct), and trabecular BMD (vBMD.tb) were measured. In diaphyseal slices, Ar.tot, vBMC.ct, cortical density (vBMD.ct), cross-sectional moment of inertia (CSMI) and calf muscle CSA (MuscA) were examined. RESULTS: In conditioned jumpers, side-to-side differences in favour of take-off leg were found in 4% slice in vBMC.tb (+4.1%) (P<0.05). A side-to-side difference was found in 66% slice vBMC.ct and CSMI (both P<0.05), with conditioned jumper (+2.8% and 6.6%) and triple jumper (+2.7% and 7.2%) values higher than other groups. CONCLUSION: The results suggest that regular training in high-impact sports with uneven lower limb loading results in side-to-side differences in skeletal adaptation independent of age and gender, suggesting that high-impact exercise is effective in maintaining bone strength throughout human lifespan.

Variability in the magnitude of response of metabolic enzymes reveals patterns of co-ordinated expression following endurance training in women.

Skeletal muscles improve their oxidative fatty acid and glucose metabolism following endurance training, but the magnitude of response varies considerably from person to person. In 20 untrained young women we examined interindividual variability in training responses of metabolic enzymes following 6 weeks of endurance training, sufficient to increase maximal oxygen uptake by 10 ± 8% (mean ± SD). Training led to increases in mitochondrial enzymes [succinate dehydrogenase (SDH; 47 ± 78%), cytochrome c oxidase (52 ± 70%) and ATP synthase (63 ± 69%)] and proteins involved in fatty acid metabolism [3-hydroxyacyl CoA dehydrogenase (69 ± 92%) and fatty acid transporter CD36 (86 ± 31%)]. Increases in enzymes of glucose metabolism [phosphofructokinase (29 ± 94%) and glucose transporter 4 (18 ± 65%)] were not significant. There was no relationship between changes in maximal oxygen uptake and the changes in the metabolic proteins. Considerable interindividual variability was seen in the magnitude of responses. The response of each enzyme was proportional to the change in SDH; individuals with a large increase in SDH also showed high gains in all other enzymes, and vice versa. Peroxisome proliferator-activated receptor γ coactivator 1α protein content increased after training, but was not correlated with changes in the metabolic proteins. In conclusion, the results revealed co-ordinated adaptation of several metabolic enzymes following endurance training, despite differences between people in the magnitude of response. Differences between individuals in the magnitude of response might reflect the influence of environmental and genetic factors that govern training adaptations.