Loss of α-actinin-3 during human evolution provides superior cold resilience and muscle heat generation.

The protein α-actinin-3 expressed in fast-twitch skeletal muscle fiber is absent in 1.5 billion people worldwide due to homozygosity for a nonsense polymorphism in ACTN3 (R577X). The prevalence of the 577X allele increased as modern humans moved to colder climates, suggesting a link between α-actinin-3 deficiency and improved cold tolerance. Here, we show that humans lacking α-actinin-3 (XX) are superior in maintaining core body temperature during cold-water immersion due to changes in skeletal muscle thermogenesis. Muscles of XX individuals displayed a shift toward more slow-twitch isoforms of myosin heavy chain (MyHC) and sarcoplasmic reticulum (SR) proteins, accompanied by altered neuronal muscle activation resulting in increased tone rather than overt shivering. Experiments on Actn3 knockout mice showed no alterations in brown adipose tissue (BAT) properties that could explain the improved cold tolerance in XX individuals. Thus, this study provides a mechanism for the positive selection of the ACTN3 X-allele in cold climates and supports a key thermogenic role of skeletal muscle during cold exposure in humans.

Discipline-specific Torque-Velocity Profiles and Musculotendinous Morphology in Athletes.

OBJECTIVES: The aim of this study was to compare torque-velocity profiles, muscle architecture, tendon dimensions, and bilateral-symmetry between competitive cyclists (CY), competitive runners (RN), ice-hockey players (IH), basketball players (BP), and physically-active individuals (CN) (n=10 for each group). METHODS: Vastus lateralis (VL) muscle and patellar tendon (PT) structures were determined with B-mode ultrasonography, and maximal knee extensor isokinetic torque was assessed at three different velocities. RESULTS: Optimal torque and velocity were lower in runners than CY, BP and IH (p<0.05). Maximal power was similar between the athlete groups but greater than CN (p<0.05). Furthermore, RN and BP reached their peak-torque at longer muscle lengths compared to IH and CY (p<0.05). RN had the lowest VL muscle thickness and the greatest fascicle length, while CY had the greatest pennation angle (p<0.05). CY had the greatest PT thickness, particularly at the proximal and medial sites, while BP at the distal point (p<0.05), with similar trends observed for PT cross-sectional-area. CONCLUSIONS: Our findings show that even if power generating capacity is similar between athletic disciplines, there are discipline-specific muscle adaptations, where particularly runners appear to have muscles adapted for speed rather than torque development, while in cyclists, velocity is sacrificed for torque development.

A modelling approach to disentangle the factors limiting muscle oxygenation in smokers.

Cigarette smoking is associated with a lower exercise capacity and lower muscle fatigue resistance. This is at least partly attributable to carboxyhaemoglobin (HbCO) in the blood that via reduction in the oxygen-carrying capacity, and the left-shift of the Hb-dissociation curve would reduce tissue oxygenation. On the other hand, a reduced oxygen uptake due to mitochondrial dysfunction would result in improved oxygenation. We used previously collected capillarisation, myoglobin and estimated cellular maximal muscle oxygen consumption data derived from succinate dehydrogenase-stained sections from the vastus lateralis muscle from six smokers and five non-smokers. These data were fed into an expanded Krogh tissue oxygenation model to assess whether an impaired muscle fatigue resistance in smokers is primarily due to HbCO or impaired mitochondrial respiration. The model showed that in smokers with 6% and 20% HbCO (causing a left-shift of the Hb-dissociation curve) average muscle oxygenation was reduced by 1.9% and 7.2%, respectively. Muscle oxygenation was increased by 13.3% when maximal mitochondrial respiration was reduced by 29%. A combination of a 29% reduction in maximal mitochondrial respiration and 20% HbCO led to no significant difference in muscle oxygenation from that in non-smokers. This indicates that while HbCO may explain the reduced exercise capacity after just one smoking session, in chronic smokers impaired mitochondrial respiration appears more important in reducing oxygen extraction and exercise capacity with only a small contribution of the left-shift of the Hb-dissociation curve.

Three-week sprint interval training (SIT) reduces cell-free DNA and low-frequency fatigue but does not induce VO2max improvement in older men.

PURPOSE: This study aimed to investigate the impact of sprint interval training (SIT) on both the acute and 3-week modulations of cell-free DNA (cfDNA), as well as its association with neuromuscular fatigue and physical performance in healthy young and old men. METHODS: Ten young (20-25 year old) and nine elderly (63-72 year old) healthy men performed nine SIT sessions consisting of 4-to-6-all-out cycling repetitions of 30 s interspaced with 4-min rest intervals. We compared the maximal voluntary contractions torque, central activation ratio, low-frequency fatigue (LFF), and cfDNA concentrations between the groups before, immediately after, 1 h after, and 24 h after the first and ninth SIT sessions. RESULTS: The plasma cfDNA levels were increased post-exercise (from 1.4 ± 0.258 to 1.91 ± 0.278 ng/ml (P < 0.01) on a log10 scale), without significant differences between the groups. However, older individuals showed a slight decrease in the baseline cfDNA values, from 1.39 ± 0.176 to 1.29 ± 0.085 ng/ml on a log10 scale, after 3 weeks (P = 0.043). Importantly, the elevation of the post-exercise cfDNA values was correlated with an increase in LFF in both groups. Three weeks of SIT induced an improvement in the recovery of LFF (main session effect, P = 0.0029); however, only the young group showed an increase in aerobic capacity (VO2max) (from 40.8 ± 6.74 to 43.0 ± 5.80 ml/kg/min, P = 0.0039). CONCLUSION: Three weeks of SIT diminished the baseline cfDNA values in the old group, together with an improvement in the recovery of LFF. However, VO2max was increased only in the young group.

Near-InfraRed Spectroscopy Provides a Reproducible Estimate of Muscle Aerobic Capacity, but Not Whole-Body Aerobic Power.

Near-infrared spectroscopy (NIRS) during repeated limb occlusions is a noninvasive tool for assessing muscle oxidative capacity. However, the method's reliability and validity remain under investigation. This study aimed to determine the reliability of the NIRS-derived mitochondrial power of the musculus vastus lateralis and its correlation with whole-body (cycling) aerobic power (V̇O2 peak). Eleven healthy active men (28 ± 10 y) twice (2 days apart) underwent repeated arterial occlusions to induce changes in muscle oxygen delivery after 15 s of electrical muscle stimulation. The muscle oxygen consumption (mV̇O2) recovery time and rate (k) constants were calculated from the NIRS O2Hb signal. We assessed the reliability (coefficient of variation and intraclass coefficient of correlation [ICC]) and equivalency (t-test) between visits. The results showed high reproducibility for the mV̇O2 recovery time constant (ICC = 0.859) and moderate reproducibility for the k value (ICC = 0.674), with no significant differences between visits (p > 0.05). NIRS-derived k did not correlate with the V̇O2 peak relative to body mass (r = 0.441, p = 0.17) or the absolute V̇O2 peak (r = 0.366, p = 0.26). In conclusion, NIRS provides a reproducible estimate of muscle mitochondrial power, which, however, was not correlated with whole-body aerobic capacity in the current study, suggesting that even if somewhat overlapping, not the same set of factors underpin these distinct indices of aerobic capacity at the different (peripheral and whole-body systemic) levels.

Impact of Anaerobic Exercise Integrated Into Regular Training on Experienced Judo Athletes: Running Vs. Repetitive Throws.

ABSTRACT: Kamandulis, S, Dudeniene, L, Snieckus, A, Kniubaite, A, Mickevicius, M, Lukonaitiene, I, Venckunas, T, Stasiule, L, and Stasiulis, A. Impact of anaerobic exercise integrated into regular training on experienced judo athletes: running vs. repetitive throws. J Strength Cond Res XX(X): 000-000, 2024-Anaerobic training in high-level athletes is of considerable interest to practitioners aiming to optimize performance. This study compared the impact of interval anaerobic training (IAT) sessions consisting of either high-intensity running or throwing that were performed twice a week together with regular judo training on the anaerobic and aerobic performance of experienced judo athletes. Employing a repeated-measures, counterbalancing, research design, 12 national team judo athletes (7 women and 5 men; mean age, 20.4 ± 0.95 years; mean judo training experience, 13.4 ± 1.4 years; competitive level, black belt first and second Dan) performed each IAT modality for 6 weeks, for a full training cycle of 12 weeks. Assessments of their anaerobic fitness (Cunningham and Faulkner Anaerobic Treadmill Test), sport-specific anaerobic fitness (Special Judo Fitness Test [SJFT]), and aerobic capacity (maximal incremental treadmill running test) were performed before, after 6 weeks, and after 12 weeks of training. The uphill running performance improved by 13.1% over the 12-week period (p = 0.047). Simultaneously, there was a 9.0% improvement in the SJFT index and a 6.9% increase in the number of throws (p = 0.011 and p = 0.017, respectively). Although a trend for throwing drills being more effective than interval sprint running was observed, the interaction effect lacked statistical significance (p = 0.074). Moreover, no substantial changes were noted in aerobic endurance markers. In conclusion, this study suggests that incorporating specific and nonspecific high-intensity drills into a routine training regimen may enhance anaerobic capacity among well-trained judo athletes, potentially leading to favorable competitive outcomes.

Relationships between weekly changes in salivary hormonal responses and load measures during the pre-season phase in professional male basketball players.

The aim of this study was to assess the relationships between weekly changes in external and internal load considered separately and jointly and salivary hormonal responses during the pre-season phase in professional male basketball players. Twenty-one professional male basketball players (mean ± standard deviation, age: 26.2 ± 4.9 years; height: 198.7 ± 6.7 cm; body mass: 93.2 ± 10.0 kg) were assessed during 5 weeks of the pre-season phase. External load was measured using microsensors and reported as PlayerLoad (PL) and PL/ min. Internal load was calculated using the session rating of perceived exertion scale (sRPE-load), summated heart rate zones (SHRZ) and percentage of maximal heart rate (%HRmax). Salivary hormone responses were monitored weekly by measuring testosterone (T), cortisol (C), and their ratio (T:C). The relationships between weekly changes in load measures considered separately and jointly and hormonal responses were assessed using linear mixed model analysis. No significant (p > 0.05) relationships were evident between weekly changes in T, C or T:C with external and internal load measures considered separately (R2-conditional = < 0.001-0.027) or jointly (R2-conditional = 0.028-0.075). Factors other than measured loads might be responsible for weekly changes in hormonal responses and therefore external and internal load measures cannot be used to anticipate weekly hormonal responses during the pre-season phase in professional basketball players.

Impact of methionine restriction on muscle aerobic metabolism and hypertrophy in young and old mice on an obesogenic diet.

Methionine restriction (MR) reduces inflammation and increases longevity. We studied the effects of MR (0.17% kCal methionine, 10% kCal fat) and MR + high-fat diet (HFD) (0.17% methionine, 45% kCal fat) and overload-induced hypertrophy on inflammation, angiogenesis and mitochondrial activity in the hind-limb muscle in 10- and 26-month-old male C57BL/6J mice. Plasma IL-6 concentrations were higher in old compared to young mice. M. plantaris hypertrophy was accompanied by increased p-Akt, without a significant change in Akt and VEGF levels. In young mice on a HFD or MR + HFD diet the SDH activity was higher than in those from mice on other diets, irrespective of overload. There were no significant differences in total NAD concentration in the m. gastrocnemius. MR enhanced the skeletal muscle hypertrophic response in old age that was accompanied with an increase in p-Akt without significant changes in muscle oxidative capacity, low-grade systemic inflammation, NAD, VEGF or Akt levels.

Increasing the resting time between drop jumps lessens delayed-onset muscle soreness and limits the extent of prolonged low-frequency force depression in human knee extensor muscles.

PURPOSE: Unaccustomed eccentric contractions generally result in a long-lasting contractile impairment, referred to as prolonged low-frequency force depression (PLFFD), and delayed-onset muscle soreness (DOMS). We here used repeated drop jumps (DJs) as an eccentric contraction model and studied the effects of increasing the time between DJs from 20 s to 5 min. We hypothesized that both PLFFD and DOMS would be less marked at the longer DJ interval due to the longer time to restore structural elements between DJs. METHODS: Young men (n = 12) randomly performed 50 DJs with either 20-s (DJ-20 s) or 5-min (DJ-5 min) rest between DJs. Voluntary, 20 Hz and 100 Hz electrically stimulated isometric knee extension torques and muscle soreness were monitored before and for 7 days after DJs; serum CK activity was measured to assess muscle fibre protein leakage. In additional experiments, changes in mRNA levels were assessed in muscle biopsies collected before and 1 h after exercise. RESULTS: A marked PLFFD was observed with both protocols and the extent of 20 Hz torque depression was smaller immediately and 1 day after DJ-5 min than after DJ-20 s (p < 0.05), whereas the MVC and 100 Hz torques were similarly decreased with the two protocols. Markedly larger differences between the two protocols were observed for the muscle soreness score, which 1-4 days after exercise was about two times larger with DJ-20 s than with DJ-5 min (p < 0.01). CONCLUSIONS: The larger protective effect of the longer DJ interval against DOMS than against PLFFD indicates that their underlying mechanisms involve different structural elements.

Cardiorespiratory Responses to Specific and Nonspecific Exercise in High-Profile Amateur Boxers.

ABSTRACT: Venckunas, T, Bruzas, V, Stasiulis, A, Snieckus, A, Mockus, P, and Kamandulis, S. Cardiorespiratory responses to specific and non-specific exercise in high-profile amateur boxers. J Strength Cond Res 36(3): 717-722, 2022-Our aim was to compare cardiorespiratory responses in 3 types of all-out exercises (upper body, lower body, and punching) in well-trained boxers and peak heart rate (HR) in these tests with HR response to competitive Olympic boxing. On 4 separate occasions, 11 male amateur boxers performed: (a) progressive treadmill running to exhaustion; (b) progressive arm cranking to failure; (c) progressive bag punching to maximal exertion; and (d) competitive boxing fight (3 × 3 minutes format). Expired gas and HR were measured in all tasks except in the full-contact competitive fight where only HR was recorded. Peak oxygen uptake (55.3 ± 5.9 ml·kg-1·min-1) was highest during treadmill running. Peak respiratory exchange ratio was highest during bag punching (1.26 ± 0.09), but did not differ between arm cranking and running. Peak HR of the boxing fight (197.7 ± 5.9 b·min-1) did not differ from that of running (196.5 ± 8.7 b·min-1), but was smaller in arm cranking (179.8 ± 9.2) and bag punching (184.1 ± 12.2 b·min-1). The correlation coefficients between peak HR achieved during competitive fighting and that achieved during running, arm cranking and bag punching were 0.720 (p = 0.013), 0.597 (p = 0.052), and 0.702 (p = 0.035), respectively. In conclusion, in high-profile amateur boxers, running evoked a higher cardiorespiratory activation than arm cranking or bag punching, whereas punching elicited the highest input of anaerobic glycolysis. Peak HR of competitive fighting was the same as during running and much higher than during arm cranking or bag punching.

Carbohydrate restriction following strenuous glycogen-depleting exercise does not potentiate the acute molecular response associated with mitochondrial biogenesis in human skeletal muscle.

PURPOSE: Carbohydrate (CHO) restriction could be a potent metabolic regulator of endurance exercise-induced muscle adaptations. Here, we determined whether post-exercise CHO restriction following strenuous exercise combining continuous cycling exercise (CCE) and sprint interval exercise could affect the gene expression related to mitochondrial biogenesis and oxidative metabolism in human skeletal muscle. METHODS: In a randomized cross-over design, 8 recreationally active males performed two cycling exercise sessions separated by 4 weeks. Each session consisted of 60-min CCE and six 30-s all-out sprints, which was followed by ingestion of either a CHO or placebo beverage in the post-exercise recovery period. Muscle glycogen concentration and the mRNA levels of several genes related to mitochondrial biogenesis and oxidative metabolism were determined before, immediately after, and at 3 h after exercise. RESULTS: Compared to pre-exercise, strenuous cycling led to a severe muscle glycogen depletion (> 90%) and induced a large increase in PGC1A and PDK4 mRNA levels (~ 20-fold and ~ 10-fold, respectively) during the acute recovery period in both trials. The abundance of the other transcripts was not changed or was only moderately increased during this period. CHO restriction during the 3-h post-exercise period blunted muscle glycogen resynthesis but did not increase the mRNA levels of genes associated with muscle adaptation to endurance exercise, as compared with abundant post-exercise CHO consumption. CONCLUSION: CHO restriction after a glycogen-depleting and metabolically-demanding cycling session is not effective for increasing the acute mRNA levels of genes involved in mitochondrial biogenesis and oxidative metabolism in human skeletal muscle.

Endurance training-induced increase in muscle oxidative capacity without loss of muscle mass in younger and older resistance-trained men.

While concurrent training is regularly used in older populations, the inverse relationship between fibre size and oxidative capacity suggests that endurance training in resistance-trained individuals may result in some loss of resistance training-induced gains in muscle mass, which may be more pronounced in older people. We investigated the impact of superimposed endurance training in younger (28.5 ± 4.8 years; n = 8) and older (67.5 ± 5.5 years; n = 7) highly resistance-trained men. Participants underwent a 10-week endurance cycling training programme consisting of five 6-min intervals at 75% max heart rate (HRmax) separated by 4-min intervals at 90% HRmax. The anatomical cross-sectional area (ACSA) of the thigh muscles, as determined with MRI, was 24% smaller in older compared to younger participants (p < 0.001). Although maximal oxygen consumption (VO2max) was also lower in the older group (p < 0.001), VO2max per kg body mass did not differ significantly between younger and older participants. Histological analyses of biopsies of the m. vastus lateralis showed that endurance training induced an increase in succinate dehydrogenase activity in both younger and older participants (p ≤ 0.043), and an increase in the number of capillaries around type I fibres (p = 0.017). The superimposed endurance training did not induce a significant decrease in thigh ACSA, fibre cross-sectional area, or knee extensor maximum voluntary isometric force. These observations indicate that adding endurance training to resistance training can lead to positive endurance-related adaptations without negative consequences for muscle size and strength in older and younger resistance-trained people.

Endurance exercise plus overload induces fatigue resistance and similar hypertrophy in mice irrespective of muscle mass.

NEW FINDINGS: What is the central question of this study? Does combining endurance and hypertrophic stimuli blunt the adaptations to both modalities and is this effect greater in muscles with larger baseline fibre cross sectional area? What is the main finding and its importance? Endurance exercise and hypertrophic stimuli can be combined to increase fatigue resistance and fibre size without blunting either adaptation regardless of baseline fibre size. ABSTRACT: Previous studies have demonstrated that fibre cross-sectional area (FCSA) is inversely related to oxidative capacity, which is thought to be determined by diffusion limitations of oxygen, ADP and ATP. Consequently, it is hypothesised that (1) when endurance training is combined with a hypertrophic stimulus the response to each will be blunted, and (2) muscles with a smaller FCSA will show a larger hypertrophic response than those with a large FCSA. To investigate this, we combined overload with endurance exercise in 12-month-old male mice from three different strains with different FCSA: Berlin High (BEH) (large fibres), C57BL/6J (C57) (normal-sized fibres) and Berlin Low (BEL) (small fibres). The right plantaris muscle was subjected to overload through denervation of synergists with the left muscle acting as an internal control. Half the animals trained 30 min per day for 6 weeks. The overload-induced hypertrophy was not blunted by endurance exercise, and the exercise-induced increase in fatigue resistance was not impaired by overload. All strains demonstrated similar absolute increases in FCSA, although the BEH mice with more fibres than the C57 mice demonstrated the largest increase in muscle mass and BEL mice with fewer fibres the smallest increase in muscle mass. This study suggests that endurance exercise and hypertrophic stimuli can be combined without attenuating adaptations to either modality, and that increases in FCSA are independent of baseline fibre size.

Carbohydrates do not accelerate force recovery after glycogen-depleting followed by high-intensity exercise in humans.

Prolonged low-frequency force depression (PLFFD) induced by fatiguing exercise is characterized by a persistent depression in submaximal contractile force during the recovery period. Muscle glycogen depletion is known to limit physical performance during prolonged low- and moderate-intensity exercise, and accelerating glycogen resynthesis with post-exercise carbohydrate intake can facilitate recovery and improve repeated bout exercise performance. Short-term, high-intensity exercise, however, can cause PLFFD without any marked decrease in glycogen. Here, we studied whether recovery from PLFFD was accelerated by carbohydrate ingestion after 60 minutes of moderate-intensity glycogen-depleting cycling exercise followed by six 30-seconds all-out cycling sprints. We used a randomized crossover study design where nine recreationally active males drank a beverage containing either carbohydrate or placebo after exercise. Blood glucose and muscle glycogen concentrations were determined at baseline, immediately post-exercise, and during the 3-hours recovery period. Transcutaneous electrical stimulation of the quadriceps muscle was performed to determine the extent of PLFFD by eliciting low-frequency (20 Hz) and high-frequency (100 Hz) stimulations. Muscle glycogen was severely depleted after exercise, with a significantly higher rate of muscle glycogen resynthesis during the 3-hours recovery period in the carbohydrate than in the placebo trials (13.7 and 5.4 mmol glucosyl units/kg wet weight/h, respectively). Torque at 20 Hz was significantly more depressed than 100 Hz torque during the recovery period in both conditions, and the extent of PLFFD (20/100 Hz ratio) was not different between the two trials. In conclusion, carbohydrate supplementation enhances glycogen resynthesis after glycogen-depleting exercise but does not improve force recovery when the exercise also involves all-out cycling sprints.

Response to Three Weeks of Sprint Interval Training Cannot Be Explained by the Exertional Level.

Background and Objectives: The all-out mode of sprint interval training (SIT) has been shown to be an efficient method for improving sports performance, exercise capacity, and aerobic fitness. Although the benefits of SIT are well described, the mechanisms underlying the different degrees of response remain largely unexplored. We aimed to assess the effects of exertion on the responsiveness to SIT. Materials and Methods: The participants were 28 young untrained men (mean ± SD age 25.7 ± 6.03 years) who exhibited either a large or small increase in Wingate test average power in response to nine SIT sessions performed over three weeks. Each training session comprised four-six bouts of 30 s all-out cycling interspaced with 4 min of rest. Individual responses were assessed using heart rate (HR) during exercise for all nine sessions, as well as blood lactate concentration up to 1 h, and the decrement in maximal voluntary knee extension torque (MVC) up to 24 h after the first and last training sessions. Peak oxygen uptake (VO2peak) and maximum HR were measured before and after training during an incremental cycling test to exhaustion. Results: Although all participants showed benefits of SIT such as increased VO2peak, the increase in anaerobic cycling power varied between participants. We identified 17 high responders and nine low responders, whose average power outputs were 0.80 ± 0.22 and 0.22 ± 0.19 W/kg, respectively. The HR achieved during any of the training sessions did not differ between high and low responders. The lactate kinetics did not differ between groups before and after the intervention. Training resulted in a more rapid recovery of MVC without any discernible differences between the high and low responders. Conclusion: The differences in the responses to SIT are not dependent on the exertion level during training.

One night of sleep deprivation impairs executive function but does not affect psychomotor or motor performance.

The current study assessed the impact of one night of sleep deprivation on cognitive, motor and psychomotor performance. Thirty healthy young adult male subjects completed a 24 h control or 24 h sleep deprived trial. For the control trial, participants (N = 15) were allowed normal night sleep (~8 h). For the sleep deprived trial, participants (N = 15) did not sleep for 24 h. Cognitive performance during go/no-go, Stroop and simple reaction tasks, psychomotor performance during speed-accuracy tasks with fixed and unfixed targets, and motor performance during countermovement jump, hand grip strength, and 30-s maximal voluntary contraction tasks were evaluated on day 1 at 8 am and 7 pm and on day 2 at 8 am. One night of sleep deprivation impaired psychological well-being and executive function but did not affect simple reaction time, the capacity for arm and leg muscle contraction, motor control performance during a speed-accuracy task with both fixed and unfixed targets, and central and peripheral motor fatigue in the 30 s maximal voluntary contraction task. The present study showed that one night of sleep deprivation resulted in executive function deterioration but did not modify motor control or maximal effort requiring performance of motor tasks.

The contribution of low-frequency fatigue to the loss of quadriceps contractile function following repeated drop jumps.

NEW FINDINGS: What is the central question of this study? Why do some subjects recover slowly following a bout of eccentric exercise and why is recovery faster following a repeated bout? What is the main finding and its importance? The results are consistent with two major causes of the reduction of quadriceps torque, the onset of low-frequency fatigue which recovered relatively fast and a second, delayed form of damage. Differences in the delayed damage process largely accounted for the differences in the rate of torque recovery between subjects after a first bout and it was suppression of the delayed damage which accounted for the faster recovery following a repeated bout of eccentric exercise. ABSTRACT: The purpose of this study was to determine the extent to which low-frequency fatigue (LFF) accounts for the loss of quadriceps strength and time course of recovery following a series of drop jumps (DJs). Seventeen female subjects (20.8 ± 1.4 years) undertook 100 DJs, which were repeated 4 weeks later. Maximum isometric torque (MIT) and the ratio of torque generated by 20 and 100 Hz electrical stimulation (20/100), as a measure of LFF, were measured over 7 days following each series of DJs. After the first series the 20/100 ratio fell to a greater extent than MIT (to 35 ± 8.7% and 69 ± 11%, respectively) but recovered over 2-3 days, while MIT showed little recovery over this time. Changes of the 20/100 ratio were similar between subjects with fast or slow MIT recovery. Following the second series of DJs, changes in the 20/100 ratio were similar to those of the first bout and there were no differences between fast and slow recovering subjects. MIT, however, recovered more rapidly than after the first bout; the faster recovery was confined to the subjects who recovered slowly following the first bout. The results are consistent with two major causes of the reduction of quadriceps torque, the onset of low-frequency fatigue which recovered relatively fast and a second, delayed, form of damage. The latter largely accounted for the differences in MIT recovery between subjects after the first bout, while suppression of the delayed damage accounted for the faster recovery following the repeated bout.

Lesions in the legs do not preclude ultra-marathon running for 100 days without pain: case report.

There is an increasing interest in participation in ultra-endurance events and a concomitant need to understand their effects on health. The effects of extremely prolonged running on leg joints, ligaments, tendons and menisci have not been explored sufficiently. The aim of the present single case study was to use ultrasonography to estimate the effects of a self-paced 8-10 hours daily running for 100 days on the morphology of joints in an experienced 47-year-old ultra-marathon runner. Examination before the start of the 100 days of running revealed already multiple but mostly mild, painless lesions in different joints of both legs. The presence of these lesions did not significantly exacerbate or cause pain during the racing. Iliotibial band bursitis and Achilles paratenonitis were however aggravated, and mild semitendinosus bursitis was a novel finding during the examination after running 8000 km in 100 days. These results are impressive because preparation for this 8000 km running was only ~5 weekly hours of training. In conclusion, this runner displayed multiple lesions in the leg joints at the start but was able to increase running volume by ~10-fold for >100 consecutive days without significantly exacerbating the pre-existing skeletomuscular abnormalities or inducing pain.

Myostatin dysfunction does not protect from fasting-induced loss of muscle mass in mice.

OBJECTIVES: The aim of the study was to investigate if myostatin dysfunction can ameliorate fasting-induced muscle wasting. METHODS: 18-week old males from Berlin high (BEH) strain with myostatin dysfunction and wild type myostatin (BEH+/+) strain were subjected to 48-h food deprivation (FD). Changes in body composition as well as contractile properties of soleus (SOL) and extensor digitorum longus (EDL) muscles were studied. RESULTS: BEH mice were heavier than BEH+/+ mice (56.0±2.5 vs. 49.9±2.8 g, P<0.001, respectively). FD induced similar loss of body mass in BEH and BEH+/+ mice (16.6±2.4 vs. 17.4±2.2%, P>0.05), but only BEH mice experienced wasting of the gastrocnemius, tibialis anterior and plantaris muscles. FD induced a marked decrease in specific muscle force of SOL. EDL of BEH mice tended to be protected from this decline. CONCLUSION: Myostatin dysfunction does not protect from loss of muscle mass during fasting.