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.

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.

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.

Improvements in muscle-tendon properties are beneficial to balance in multiple sclerosis

A 63-year-old male was diagnosed with multiple sclerosis (MS) two years prior to this investigation. We hypothesized that compromised postural balance in MS can be improved by training-induced alterations in muscle-tendon properties. Sixteen weeks of strength and balance training induced an increase in quadriceps and gastrocnemius muscle size, strength, central activation, muscle recruitment and tendon stiffness. Concomitantly, the ability to maintain postural stances was increased in both eyes-open and eyes-closed conditions. We concluded that improvements in muscle-tendon properties were accompanied by improved balance and a general feeling of well-being after training.

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.

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

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.

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.

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.

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.

HIF1A P582S gene association with endurance training responses in young women

Sequence variations in the gene encoding the hypoxia-inducible factor-1alpha, HIF1A, have been associated with physiologic function and could be associated with exercise responses. In the HIF1A P582S gene polymorphism (C1772T; rs 11549465 C/T), a single nucleotide transition from C → T alters the codon sequence from the usual amino acid; proline (C-allele), to serine (T-allele). This polymorphism was examined for association with endurance training responses in 58 untrained young women who completed a 6-week laboratory-based endurance training programme. Participant groups were defined as CC homozygotes versus carriers of a T-allele (CC vs. CT genotypes). Adaptations were examined at the systemic-level, by measuring [Formula: see text] and the molecular-level by measuring enzymes determined from vastus lateralis (n = 20): 3-hydroacyl-CoA-dehydrogenase (HAD), which regulates mitochondrial fatty acid oxidation; cytochrome C oxidase (COX-1), a marker of mitochondrial density; and phosphofructokinase (PFK), a marker of glycolytic capacity. CT genotypes showed 45% higher training-induced gains in [Formula: see text] compared with CC genotypes (P < 0.05). At the molecular level, CT increased the ratios PFK/HAD and PFK/COX-1 (47 and 3%, respectively), while in the CC genotypes these ratios were decreased (-26 and -54%, respectively). In conclusion, the T-allele of HIF1A P582S was associated with greater gains in [Formula: see text] following endurance training in young women. In a sub-group we also provide preliminary evidence of differential muscle metabolic adaptations between genotypes.

Effects of alfacalcidol on the contractile properties of the gastrocnemius medialis muscle in adult and old rats

Vitamin D deficiency is associated with muscle weakness. It is unknown, however, how supra-physiological levels of vitamin D affect skeletal muscle. To investigate the effects of increased serum vitamin D (1,25 (OH)₂D₃ or 1,25D) levels on the contractile properties of the medial gastrocnemius muscle, adult and old female Fischer₃₄₄ x Brown Norway F1 rats were orally treated with vehicle or the vitamin D analogue alfacalcidol for 1 or 6 weeks. Alfacalcidol treatment resulted in elevated 1,25D serum levels. This was accompanied by hypercalcaemia and a reduction in body mass, the latter largely attributable to a reduced food intake. However, kidney function, as reflected by normal creatinine serum levels, as well as heart mass were unaffected. The 17% reduction in maximal isometric force and power was explicable by a similar loss of muscle mass. The force-frequency relationship of the 6-week-treated old rats was shifted to the left, but neither the shape of the force-velocity relationship nor the fatigability of the muscle were altered. Supra-physiological doses of vitamin D were accompanied by significant reductions in body and muscle mass, but not by an improvement in muscle functioning. Weight loss was largely due to a reduced food intake, while the left shift in the force-frequency relation may be due to increased 1,25D levels.

Effects of oxidation on the power of chemically skinned rat soleus fibres

Oxidation alters calcium sensitivity, and decreases maximum isometric force (Po) and shortening velocity (Vmax) of single muscle fibres. To examine the effect of oxidation on the curvature of the force-velocity relationship, which determines muscle power in addition to Po and Vmax, skinned rat type I fibres were maximally activated at 15°C in a solution with pCa 4.5 and subjected to isotonic contractions before and after 4-min incubation in 50 mM H₂O₂ (n=10) or normal relaxing solution (n=3). In five oxidised and four control fibres the rate of force redevelopment (ktr), following a rapid release and re-stretch, was measured. This gives a measure of the sum of the rate constants for cross-bridge attachment (f) and detachment (g₁): (f+g₁). H₂O₂ reduced Po, Vmax and ktr by 19%, 21% and 24% respectively (P<0.001), while the shape of the force-velocity relationship was unchanged. Fitting data to the Huxley cross-bridge model suggested that oxidation decreased both the rate constant for cross-bridge attachment (f), and detachment of negatively strained cross-bridges (g₂), similar to the effect of reduced activation. This suggests that oxidative modification is a possible cause of the variation in contractile properties between muscle fibres of the same type.

Effects of submaximal activation on the determinants of power of chemically skinned rat soleus fibres

Reducing the activating calcium concentration with skinned fibres is known to decrease isometric force and maximal shortening velocity, both of which will reduce the peak power. However, power is also a function of the curvature of the force-velocity relationship, and there is limited information on how changes in activating calcium affect this important property of muscle fibres. Force-velocity relationships of permeabilized single type I fibres from rat soleus muscle were determined using isotonic contractions at 15°C with both maximal (pCa 4.5) and submaximal activation (pCa 5.6). The rate of tension redevelopment (k(tr)), which provides a measure of sum of the apparent rate constants for cross-bridge attachment and detachment (f(app) + g(app)) following a rapid release and restretch, was also measured. Compared with pCa 4.5, specific tension (P(o)) at pCa 5.6 declined by 22 ± 8% (mean ± s.d.) and the maximal velocity of shortening (V(max)) fell by 44 ± 7%, but curvature of the force-velocity relationship (a/P(o)) rose by 47 ± 31%, indicating a less concave relationship. The value of k(tr) declined by 23 ± 7%. The change in a/P(o) reduced the impact of changes in P(o) and V(max) on peak power by approximately 25%. Fitting the data to Huxley's model of cross-bridge action suggests that lower activating calcium decreased both the rate constant for cross-bridge attachment (f) and that for detachment of negatively strained cross-bridges (g(2)). The fact that V(max) (and thus g(2)) changed to a greater extent than k(tr) (f(app) + g(app)) is the reason that reduced activation results in a reduction in curvature of the force-velocity relationship.

Reporting whole-body vibration intervention studies: recommendations of the International Society of Musculoskeletal and Neuronal Interactions

Whole-body vibration (WBV) is receiving increasing interest as a therapeutic modality to improve neuromuscular performance or to increase bone mass or density. In order to help improve the quality of reports about WBV treatment studies, the International Society of Musculoskeletal and Neuronal Interactions (ISMNI) invited experts in the field to provide suggestions on how the intervention should be described in such reports. The recommendations are presented here.

Resistance training increases in vivo quadriceps femoris muscle specific tension in young men

AIM

The present study investigated whether in vivo human quadriceps femoris (QF) muscle specific tension changed following strength training by systematically determining QF maximal force and physiological cross-sectional area (PCSA).

METHODS

Seventeen untrained men (20 +/- 2 years) performed high-intensity leg-extension training three times a week for 9 weeks. Maximum tendon force (F(t)) was calculated from maximum voluntary contraction (MVC) torque, corrected for agonist and antagonist muscle activation, and moment arm length (d(PT)) before and after training. QF PCSA was calculated as the sum of the four component muscle volumes, each divided by its fascicle length. Dividing F(t) by the sum of the component muscle PCSAs, each multiplied by the cosine of the respective fascicle pennation angle, provided QF specific tension.

RESULTS

MVC torque and QF activation increased by 31% (P < 0.01) and 3% (P < 0.05), respectively, but there was no change in antagonist co-activation or d(PT). Subsequently, F(t) increased by 27% (P < 0.01). QF volume increased by 6% but fascicle length did not change in any of the component muscles, leading to a 6% increase in QF PCSA (P < 0.05). Fascicle pennation angle increased by 5% (P < 0.01) but only in the vastus lateralis muscle. Consequently, QF specific tension increased by 20% (P < 0.01).

CONCLUSION

An increase in human muscle specific tension appears to be a real consequence of resistance training rather than being an artefact of measuring errors but the underlying cause of this phenomenon remains to be determined.

The role of systemic inflammation in age-related muscle weakness and wasting

Ageing is associated with a slow, but progressive muscle weakness, which is largely attributable to muscle wasting. A diminished function of satellite cells at old age may hamper preservation and repair from (contraction)-induced injury and contribute to the age-related muscle wasting. Satellite cell function may be affected by circulating factors, as muscle regeneration in old mice sharing the circulation of young mice is not impaired. Chronic low-grade systemic inflammation in old organisms may be that environmental factor. Indeed, the inflammatory cytokine tumor necrosis factor-alpha (TNFalpha) negatively affects the muscle regenerating capacity. TNFalpha destabilizes MyoD, a muscle-specific transcription factor involved in satellite cell proliferation and differentiation, and induces apoptosis of satellite cells, particularly at old age. Here it is proposed that some of these effects are mediated by TNFalpha-induced expression of inhibitors of differentiation proteins. Yet, the increase in TNFalpha during the normal inflammatory response helps, rather than impairs, the repair process. This apparent contradiction may be resolved by the fact that the effects of TNFalpha are concentration and time dependent. Thus, the negative effect of systemic inflammation on muscle strength at old age may only become apparent when it exceeds a certain threshold and persists for a prolonged period.

Disproportionate changes in skeletal muscle strength and size with resistance training and ageing

The ability of a muscle to shorten and produce force is crucial for locomotion, posture, balance and respiration. During a contraction, myosin heads on the myosin filament propel the actin filament via ATP hydrolysis, resulting in shortening of the muscle and/or force generation. The maximal shortening velocity of a muscle fibre is largely determined by the myosin ATPase activity, while maximal force is primarily determined by the cross-sectional area. Since most muscles are pennate rather than parallel-fibred and work at different lever ratios, muscle architecture and joint-tendon anatomy has to be taken into account to obtain the force and velocity characteristics of a muscle. Additionally, the recruitment of agonistic and antagonistic muscles will contribute to the torque generated during a contraction. Finally, tendon compliance may impact on the rate of force rise and force generated if it is such that the muscle contraction proceeds in the ascending limb of the length-tension relation. Even when magnetic resonance imaging and ultrasound, combined with EMG and/or electrical stimulation, have been applied to relate changes in muscle contractile properties to alterations in muscle size and architecture during ageing and resistance training, a disproportionate change in muscle strength and size remains to be explained.

Region-specific adaptations in determinants of rat skeletal muscle oxygenation to chronic hypoxia

Chronic exposure to hypoxia is associated with muscle atrophy (i.e., a reduction in muscle fiber cross-sectional area), reduced oxidative capacity, and capillary growth. It is controversial whether these changes are muscle and fiber type specific. We hypothesized that different regions of the same muscle would also respond differently to chronic hypoxia. To investigate this, we compared the deep (oxidative) and superficial (glycolytic) region of the plantaris muscle of eight male rats exposed to 4 wk of hypobaric hypoxia (410 mmHg, Po(2): 11.5 kPa) with those of nine normoxic rats. Hematocrit was higher in chronic hypoxic than control rats (59% vs. 50%, P < 0.001). Using histochemistry, we observed 10% fiber atrophy (P < 0.05) in both regions of the muscle but no shift in the fiber type composition and myoglobin concentration of the fibers. In hypoxic rats, succinate dehydrogenase (SDH) activity was elevated in fibers of each type in the superficial region (25%, P < 0.05) but not in the deep region, whereas in the deep region but not the superficial region the number of capillaries supplying a fiber was elevated (14%, P < 0.05). Model calculations showed that the region-specific alterations in fiber size, SDH activity, and capillary supply to a fiber prevented the occurrence of anoxic areas in the deep region but not in the superficial region. Inclusion of reported acclimatization-induced increases in mean capillary oxygen pressure attenuated the development of anoxic tissue areas in the superficial region of the muscle. We conclude that the determinants of tissue oxygenation show region-specific adaptations, resulting in a marked differential effect on tissue Po(2).

Carbon monoxide inhalation reduces skeletal muscle fatigue resistance

AIM

To determine whether inhalation of carbon monoxide (CO), resulting in carboxyhaemoglobin (COHb) levels observed in smokers, had an effect on muscle fatigue during electrically evoked and voluntary muscle contractions.

METHODS

Young non-smoking males inspired CO from a Douglas bag until their COHb level reached 6%. During the control condition the same participants inspired ambient air from a Douglas bag for 6 min. Fatigue was assessed as the decline in torque in isometric knee extensions, during 2 min of electrically evoked contractions (30 Hz, 1 s on, 1 s off) and during 2 min of maximal isometric voluntary contractions (1 s on, 1 s off). A fatigue index (FI) was calculated as the ratio of final torque : initial torque. Time to peak torque (TPT) and half relaxation time ((1/2)RT) were also determined for the electrically evoked contractions.

RESULTS

The FI during both the voluntary fatigue test (control: 0.80 +/- 0.09 vs. CO: 0.70 +/- 0.08; mean +/- SD) and that of the fatigue test with electrically evoked contractions (control: 0.61 +/- 0.09 vs. CO: 0.53 +/- 0.12) was significantly lower after CO inhalation than after inhalation of ambient air (P < 0.05). There was, however, no effect of CO on the changes in TPT or (1/2)RT during the fatigue test.

CONCLUSION

Carbon monoxide inhalation resulting in COHb levels found in smokers has an acute impact on the ability of the muscle to resist fatigue.

Muscle fatigue resistance during stimulated contractions is reduced in young male smokers

AIM

To determine whether muscle function is compromised in healthy smokers in comparison with activity-matched non-smokers.

METHODS

Nine male smokers (aged 22.2 +/- 2.5 years: mean +/- SD) with a smoking history of 2.5 +/- 3.1 pack years, and ten male control participants (25.4 +/- 2.9 years) matched for physical activity level participated in this study. Knee extensor strength was measured using isometric maximal voluntary contractions. Voluntary activation of the quadriceps and co-activation of the biceps femoris were determined using interpolated twitches and surface electromyography respectively. The frequency-torque relationship and fatigue resistance were assessed with electrically evoked contractions. A fatigue index was determined as the ratio of final torque to initial torque during a series of isometric contractions (2 min; 30 Hz; 1 s contraction/1 s rest). Quadriceps anatomical cross sectional area was measured with MRI at 50% of femur length.

RESULTS

Maximal voluntary contraction torque, quadriceps anatomical cross sectional area, knee extensor torque/quadriceps cross sectional area, activation, co-activation and force-frequency relationship were similar, whereas the fatigue index was 17% lower in smokers than non-smokers.

CONCLUSION

In young men smoking does not significantly affect quadriceps muscle mass and contractile properties, but does reduce fatigue resistance of the quadriceps muscle, which was not attributable to differences in physical activity.

The acute effect of stretching on the passive stiffness of the human gastrocnemius muscle tendon unit

Passive stretching is commonly used to increase limb range of movement prior to athletic performance but it is unclear which component of the muscle-tendon unit (MTU) is affected by this procedure. Movement of the myotendinous junction (MTJ) of the gastrocnemius medialis muscle was measured by ultrasonography in eight male participants (20.5 +/- 0.9 years) during a standard stretch in which the ankle was passively dorsiflexed at 1 deg s(-1) from 0 deg (the foot at right angles to the tibia) to the participants' volitional end range of motion (ROM). Passive torque, muscle fascicle length and pennation angle were also measured. Standard stretch measurements were made before (pre-) and after (post-) five passive conditioning stretches. During each conditioning stretch the MTU was taken to the end ROM and held for 1 min. Pre-conditioning the extension of the MTU during stretch was taken up almost equally by muscle and tendon. Following conditioning, ROM increased by 4.6 +/- 1.5 deg (17%) and the passive stiffness of the MTU was reduced (between 20 and 25 deg) by 47% from 16.0 +/- 3.6 to 10.2 +/- 2.0 Nm deg(-1). Distal MTJ displacement (between 0 and 25 deg) increased from 0.92 +/- 0.06 to 1.16 +/- 0.05 cm, accounting for all the additional MTU elongation and indicating that there was no change in tendon properties. Muscle extension pre-conditioning was explicable by change in length and pennation angle of the fascicles but post-conditioning this was not the case suggesting that at least part of the change in muscle with conditioning stretches was due to altered properties of connective tissue.

Recruitment of single muscle fibers during submaximal cycling exercise

In literature, an inconsistency exists in the submaximal exercise intensity at which type II fibers are activated. In the present study, the recruitment of type I and II fibers was investigated from the very beginning and throughout a 45-min cycle exercise at 75% of the maximal oxygen uptake, which corresponded to 38% of the maximal dynamic muscle force. Biopsies of the vastus lateralis muscle were taken from six subjects at rest and during the exercise, two at each time point. From the first biopsy single fibers were isolated and characterized as type I and II, and phosphocreatine-to-creatine (PCr/Cr) ratios and periodic acid-Schiff (PAS) stain intensities were measured. Cross sections were cut from the second biopsy, individual fibers were characterized as type I and II, and PAS stain intensities were measured. A decline in PCr/Cr ratio and in PAS stain intensity was used as indication of fiber recruitment. Within 1 min of exercise both type I and, although to a lesser extent, type II fibers were recruited. Furthermore, the PCr/Cr ratio revealed that the same proportion of fibers was recruited during the whole 45 min of exercise, indicating a rather constant recruitment. The PAS staining, however, proved inadequate to fully demonstrate fiber recruitment even after 45 min of exercise. We conclude that during cycling exercise a greater proportion of type II fibers is recruited than previously reported for isometric contractions, probably because of the dynamic character of the exercise. Furthermore, the PCr/Cr ratio method is more sensitive in determining fiber activation than the PAS stain intensity method.

Age-related skeletal muscle dysfunction: causes and mechanisms

Age-related muscle weakening may ultimately result in the transition from an independent to a dependent life-style. The decline in muscle strength is larger than expected from the loss of muscle mass. Single fibre studies and in vitro motility assays indicate that part of the muscle dysfunction is due to modifications of the myosin molecule. A lower rate of protein turnover may increase the chance of post-translational modifications such as oxidation and glycation. The impaired regenerative capacity of old muscles is related to a lower differentiation capacity of myosatellite cells, which is most likely due to altered transcriptional activity of myogenic regulatory factors (MRFs). However, old myosatellite cells can be rejuvenated when exposed to serum from young individuals. This indicates that alterations in the environment of the satellite cells or circulating substances play an important role in impaired differentiation capacity of satellite cells in old age. It is proposed that systemic inflammation may be that factor. Indeed, the inflammatory cytokine tumour necrosis factor-alpha: 1) impairs transcriptional regulation by MRFs, 2) suppresses myosatellite cell differentiation and 3) induces apoptosis. Moreover, muscle mass, strength and the response to strength training in old age are all inversely related to the degree of systemic inflammation.

Application of skinned single muscle fibres to determine myofilament function in ageing and disease

The chemically skinned fibre is a suitable preparation to determine whether alterations in myofilament function contribute to muscle dysfunction during ageing and disorders such as chronic obstructive pulmonary disease (COPD). In this preparation the sarcolemma is chemically permeabilized and the myofilament lattice kept intact, functioning under controlled near-physiological conditions. As force generating capacity is an important determinant of muscle function and is related to fibre crosssectional area (FCSA), we compared several methods employed by researchers to determine FCSA. Specific tension, force divided by FCSA, has a co-efficient of variation of 27%, 37%, or 30% when the FCSA was measured from the width and depth assuming an elliptical circumference, the width assuming a circular circumference, and the width while the fibre was suspended in the air, respectively. The last method showed the closest relation with the FCSA in histological sections. The velocity of maximal unloaded shortening (V(0)) varied with fibre type, with fibres expressing the Beta/slow (type I) myosin heavy chain (MyHC) isoform being the slowest and fibres expressing the IIb MyHC isoform the fastest. While muscle weakness experienced after surgery could not be explained by changes in specific tension or FCSA of individual fibres, the preparation revealed significant changes in myofilament function during ageing and COPD.

Control of muscle size during disuse, disease, and aging

Skeletal muscle is a highly plastic tissue. For example, muscle hypertrophies during strength training and increases its oxidative capacity in response to endurance training. Conditions associated with disuse, however, are also accompanied by adaptations, of which atrophy and a slow-to-fast transition are most prominent. Fast and slow muscles respond differently to disuse. The different response of muscle to different models of disuse reveals that loading is most important, but that also activity level, neurotrophic factors, and ageing play a part in determining the mass, morphology, contractile properties, and fatigability of a muscle. Muscle loss during disuse is a result, at least in part, of apoptosis. Finally, skeletal muscle wasting and remodelling during ageing and chronic disorders, such as chronic heart failure and chronic obstructive pulmonary disease, are not entirely attributable to disuse, but are also related to secondary consequences of the disease, most notably inflammation. Besides activating other pathways, we present evidence that inflammation during ageing and chronic disorders causes muscle wasting via alterations in abundance and/or activity of muscle specific transcription factors and induction of apoptosis, and that systemic inflammation rather than disuse is the primary cause of muscle wasting during ageing and chronic disorders.

Specific and sustained down-regulation of genes involved in fatty acid metabolism is not a hallmark of progression to cardiac failure in mice

Preferential and specific down-regulation of genes involved in fatty acid (FA) uptake and metabolism is considered a hallmark of severe hypertrophic remodeling and progression to cardiac failure. Therefore, we investigated the time course of changes in cardiac metabolic gene expression (1) in mice subjected to regional myocardial infarction (MI) for 4 days, 1 month, or 3 months and (2) in mice overexpressing calcineurin (Cn) which initially develop concentric hypertrophy progressing after the age of 4 weeks to dilated cardiomyopathy and failure. In both models, hypertrophy was characterized by increased expression of beta-myosin heavy chain protein and atrial natriuretic factor mRNA, indicative of marked structural remodeling. Fractional shortening progressively decreased from 31% to 15.1% and 3.7% 1 and 3 months after MI, respectively. One month post-MI, the expression of several metabolic genes, i.e., acyl-CoA synthetase (-50%), muscle-type carnitine palmitoyl transferase 1 (-37%) and citrate synthase (-28%), was significantly reduced in the surviving myocardium. Despite overt signs of cardiac failure 3 months post-MI, the expression of these genes had returned to normal levels. In hearts of both 4- and 6-week-old Cn mice, genes involved in both FA and glucose metabolism and mitochondrial citrate synthase were down-regulated, reflecting an overall decline in metabolic gene expression, rather than a specific and preferential down-regulation of genes involved in FA uptake and metabolism. These findings challenge the concept that specific and sustained down-regulation of genes involved in FA uptake and metabolism represents a hallmark of the development of cardiac hypertrophy and progression to failure.

Skeletal muscle contractility is preserved in COPD patients with normal fat-free mass

AIM

Peripheral muscle dysfunction often occurs in patients with chronic obstructive pulmonary disease (COPD). The muscle dysfunction may be caused by a loss of force-generating capacity, resulting from a loss of muscle mass, as well as by other alterations in contractile properties of skeletal muscle.

METHODS

The maximal isometric voluntary strength and fatigability were determined in hand-grip and quadriceps muscles from nine male COPD patients (FEV(1) 30-50% predicted) and control subjects matched for fat-free mass (FFM), physical activity level and age. Contractile properties and fatigability of the quadriceps muscle were also studied with electrically evoked isometric contractions.

RESULTS

The maximal voluntary force (MVC) and fatigability of the handgrip muscle did not differ between the COPD patients and control subjects. Also the MVC of the quadriceps muscle and the rate of force rise, contraction time, force-frequency relationship and fatigability, as determined with electrically evoked contractions, were similar in patients with COPD and control subjects.

CONCLUSION

Skeletal muscle strength, contractile properties and fatigability are preserved in patients with moderate COPD and a normal FFM and activity level. This suggests that skeletal muscle dysfunction does not take place during moderate COPD until cachexia and/or a decline in physical activity occur.

Expression of Ankrd2 in fast and slow muscles and its response to stretch are consistent with a role in slow muscle function

In striated muscle, the structural genes associated with muscle fiber phenotype determination as well as muscle mass accretion are regulated largely by mechanical stimuli. Passive stretch of skeletal muscle stimulates muscle growth/hypertrophy and an increased expression of slow muscle genes. We previously identified Ankyrin repeat-domain protein (Ankrd2) as a novel transcript expressed in fast tibialis anterior muscles after 7 days of passive stretch immobilization in vivo. Here, we test the hypothesis that the expression of Ankrd2 in stretched fast muscle is associated with the stretch-induced expression of slow muscle phenotype rather than the hypertrophic response. Our results show that, in 4- and 7-day stretched tibialis anterior muscle, the expression of Ankrd2 mRNA and protein was significantly upregulated (P > 0.001). However, in fast muscles of kyphoscoliotic mutant mice, which lack the hypertrophic response to overload but have a slower muscle phenotype than wild-type, Ankrd2 expression was significantly upregulated. The distribution pattern of Ankrd2 in fast and slow muscle is also in accord with their slow fiber composition. Furthermore, it was markedly downregulated in denervated rat soleus muscle, which produces a pronounced shift toward the fast muscle phenotype. Using a sensitive proteomics approach (Ciphergen Technology), we observed that Ankrd2 protein was undetectable in soleus after 4 wk of denervation. We suggest that Ankrd2, which is also a titin binding protein, is a stretch-response gene associated with slow muscle function and that it is part of a separate mechanotransduction system to the one that regulates muscle mass.

Functional and metabolic adaptation of the heart to prolonged thyroid hormone treatment

In heart failure, thyroid hormone (TH) treatment improves cardiac performance. The long-term effects of TH on cardiac function and metabolism, however, are incompletely known. To investigate the effects of up to 28 days of TH treatment, male Wistar rats received 3,3',5-triiodo-l-thyronine (200 microg/kg sc per day) leading to a 2.5-fold rise in plasma fatty acid (FA) level and progressive cardiac hypertrophy (+47% after 28 days) (P < 0.001). Ejection fraction (echocardiography) was increased (+12%; P < 0.05) between 7 and 14 days and declined thereafter. Neither cardiac FA oxidation, glycolytic capacity (homogenates) per unit muscle mass, nor mRNA levels of proteins involved in FA and glucose uptake and metabolism (Northern blots and microarray) were altered. After 28 days of treatment, mRNA levels of uncoupling proteins (UCP) 2 and 3 and atrial natriuretic factor were increased (P < 0.05). This indicates that TH-induced hypertrophy is associated with an initial increase in cardiac performance, followed by a decline in cardiac function and increased expression of UCPs and atrial natriuretic factor, suggesting that detrimental effects eventually prevail.

Glyceraldehyde-3-phosphate dehydrogenase varies with age in glycolytic muscles of rats

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA, protein, and enzyme activity levels in hindlimb muscles of adult and senescent Fischer 344 x Brown Norway rats were investigated. Soleus muscles from adult and senescent rats had similar levels of GAPDH. In contrast, muscles containing a large proportion of glycolytic fibers had lower GAPDH levels in senescent rats relative to these muscles in adult rats; this was observed at both the mRNA and protein levels. These data indicate that skeletal muscle glycolytic capacity of fast muscles is diminished with age and that it may be caused by changes at the level of transcription. Also, because GAPDH mRNA levels change with age in several rat muscles, GAPDH mRNA is not always a proper internal control for mRNA analyses of aging skeletal muscle.

The influence of thyroid hormone on myosin isoform composition and shortening velocity of single skeletal muscle fibres with special reference to ageing and gender

This review summarizes the effects of altered thyroid hormone levels on the expression of myosin isoforms and contractility in single muscle fibres from fast- and slow-twitch muscles from young and old male and female rats. The differences between male and female hyperthyroid soleus muscles are suggested to be related to an interaction of thyroid hormones and sex hormones in the regulation of myosin gene expression. Additionally, the mismatch between the protein and mRNA levels of MyHCs between male and female hyperthyroid extensor digitorum longus (EDL) muscles raises the possibility of a gender-related difference in post-transcriptional, translational or post-translational regulation of MyHC isoforms by T3.

Post-operative effects on insulin resistance and specific tension of single human skeletal muscle fibres

Surgery and accidental trauma are associated with a transient period of insulin resistance, substrate catabolism and muscle weakness. In the present study, we evaluated the changes in the force-generating capacity of chemically skinned single muscle fibres following abdominal surgery. Biopsies of the m. vastus lateralis were obtained in three patients 1 day before and 3 or 6 days after surgery. Part of the biopsy was frozen for histochemical analysis of the fibre cross-sectional area (FCSA) and myofibrillar protein content, and another part was used for single-fibre contractile measurements. All patients developed insulin resistance following surgery. The maximum velocity of unloaded shortening of single muscle fibres did not change following surgery. The FCSA did not decrease after surgery, as determined either from histochemical sections or from single fibres measured at a fixed sarcomere length of 2.76+/-0.09 microm (mean+/-S.D.). Further, the force-generating capacity of the single fibres, measured as maximal Ca(2+)-activated force (P(0)) or as P(0) normalized to FCSA (specific tension), remained unchanged, as did the myofibrillar protein content of the muscle. In conclusion, the muscle weakness associated with post-operative insulin resistance is not related to a decreased specific tension or a loss of myofibrillar proteins. Other potential cellular mechanisms underlying post-operative weakness are discussed.

Age-related changes in the microcirculation of skeletal muscle

The age-related reduction in exercise capacity is associated with a reduction in cardiac output and maximal oxygen consumption (VO2max). The loss of muscle mass explains a large portion of the age-related decline in VO2max. The capillary supply to a muscle fibre is primarily determined by its size, but also by its metabolic profile and the metabolic profile of surrounding fibres. Thus the age-related fibre atrophy and changes in the fibre type composition are expected to be accompanied by changes in the capillarisation. The exchange of oxygen, blood-borne energy sources, metabolites and heat between the blood and muscle tissue takes place in the microcirculation. Changes in the microcirculation may thus affect the functioning and viability of the muscle. The resting blood flow is minimally affected by age, but blood flow during or following exercise is generally reduced. This may in part be due to a reduced vasodilatory capacity and a decreased capillarisation. However, the coupling between capillary supply to a fibre and its metabolic profile or the profile of the surrounding fibres is maintained. There are some changes in ultrastructure of the endothelium. The age-related changes in the microcirculation are associated with a reduced VO2max and exercise capacity. The adaptability of the microcirculation is maintained at old age.