Soleus muscle stability in wild hibernating black bears

Based on studies of fast skeletal muscles, hibernating black and brown bears resist skeletal muscle atrophy during months of reduced physical activity and not feeding. The present study examined atrophy sparing in the slow soleus muscle, known to be highly prone to disuse atrophy in humans and other mammals. We demonstrated histochemically that the black bear soleus is rich in slow fibers, averaging 84.0 ± 6.6%. The percentages of slow fibers in fall (87.3 ± 4.9%) and during hibernation (87.1 ± 5.6%) did not differ ( P = 0.3152) from summer. The average fiber cross-sectional area to body mass ratio (48.6 ± 11.7 µm²/kg) in winter hibernating bears was not significantly different from that of summer (54.1 ± 11.8 µm²/kg, P = 0.4186) and fall (47.0 ± 9.7 µm²/kg, P = 0.9410) animals. The percentage of single hybrid fibers containing both slow and fast myosin heavy chains, detected biochemically, increased from 2.6 ± 3.8% in summer to 24.4 ± 24.4% ( P = 0.0244) during hibernation. The shortening velocities of individual hybrid fibers remained unchanged from that of pure slow and fast fibers, indicating low content of the minority myosins. Slow and fast fibers in winter bears exhibited elevated specific tension (kN/m²; 22%, P = 0.0161 and 11%, P = 0.0404, respectively) and maintained normalized power. The relative stability of fiber type percentage and size, fiber size-to-body mass ratio, myosin heavy chain isoform content, shortening velocity, power output, and elevated specific tension during hibernation validates the ability of the black bear to preserve the biochemical and performance characteristics of the soleus muscle during prolonged hibernation.

Skeletal muscle plasticity with marathon training in novice runners

The purpose of this study was to investigate leg muscle adaptation in runners preparing for their first marathon. Soleus and vastus lateralis (VL) biopsies were obtained from six recreational runners (23 ± 1 years, 61 ± 3 kg) before (T1), after 13 weeks of run training (T2), and after 3 weeks of taper and marathon (T3). Single muscle fiber size, contractile function (strength, speed, and power) and oxidative enzyme activity [citrate synthase (CS)] were measured at all three time points, and fiber type distribution was determined before and after the 16-week intervention. Training increased VO(2max) ∼9% (P<0.05). All soleus parameters were unchanged. VL MHC I fiber diameter increased (+8%; P<0.05) from T1 to T2. VL MHC I V(o) (-12%), MHC I power (-22%) and MHC IIa power (-29%) were reduced from T1 to T2 (P<0.05). No changes in VL single fiber contractile properties were observed from T2 to T3. No change was observed in soleus CS activity, whereas VL CS activity increased 66% (P<0.05). Our observations indicate that modest marathon training elicits very specific skeletal muscle adaptations that likely support the ability to perform 42.2 km of continuous running - further strengthening the existing body of evidence for skeletal muscle specificity.

Effects of 84-days of bedrest and resistance training on single muscle fibre myosin heavy chain distribution in human vastus lateralis and soleus muscles

AIM

This investigation determined the effects of 84 days of bedrest on the composition of myosin heavy chain (MHC) in single skeletal muscle fibres with and without a resistance-training countermeasure programme.

METHODS

Muscle biopsies were obtained from the m. vastus lateralis (VL) and m. soleus (SOL) before and after 84 days of bedrest. While control (BR) subjects (VL n = 9; SOL n = 3) refrained from exercise, BRE subjects (VL n = 8; SOL n = 3) performed knee extensor and plantar flexor resistance exercise every third day. Approximately 110 fibres per sample were analysed for MHC composition using SDS-PAGE.

RESULTS

BR-VL had 16 and 14% decreases (P < 0.05) in MHC I and IIa fibres, respectively. There were 10% increases (P < 0.05) in MHC I/IIa, IIa/IIx, I/IIa/IIx, and a approximately 30% increase (P < 0.05) in total hybrid fibres. BRE-VL showed a 15% reduction (P < 0.05) in MHC I fibres, no change in MHC IIa fibres, and a 13% increase (P < 0.05) in total hybrids. BR-SOL had a 19% decrease (P < 0.05) in MHC I fibres with a 22% increase in total hybrids. BRE-SOL showed no change in MHC composition across all fibre types.

CONCLUSION

These data suggest that the exercise countermeasures programme prevented MHC shifts in the SOL and mitigated MHC shifts in the VL. Furthermore, in the VL it appears that the resistance training programme employed in this investigation during bedrest, emphasized the use of MHC IIa phenotype muscle fibres.

Mitogen-activated protein kinase (MAPK) pathway activation: effects of age and acute exercise on human skeletal muscle

The purpose of this investigation was to examine the activation (phosphorylation) and total protein content of MAPK signalling cascade proteins (ERK 1/2, p90RSK, Mnk 1, eIF4E, p38 MAPK, JNK/SAPK, MKP 1) at rest and following exercise, in sedentary young and old men. Eight young (22 +/- 1 years; YM) and eight old (79 +/- 3 years; OM) men underwent a resting muscle biopsy of the vastus lateralis; they then performed a knee extensor resistance exercise session (29 contractions at approximately 70 % of max), followed by a post-exercise biopsy. Western immunoblot analysis demonstrated that the OM had higher resting phosphorylation of ERK 1/2, p90RSK, Mnk 1, p38 MAPK and JNK/SAPK proteins versus YM (P < 0.05). The resistance exercise bout caused an increase in phosphorylation of the ERK 1/2, p90RSK and Mnk 1 proteins (P < 0.05) in the YM. Conversely, the OM had a decrease in ERK 1/2, p90RSK, Mnk 1, p38 MAPK and JNK/SAPK phosphorylation (P < 0.05) after the exercise bout. Neither group showed a change in eIF4E phosphorylation. The total amount of protein expression of the MAPK signalling proteins was not different between the YM and OM, except that there was a higher (P < 0.05) MKP 1 protein content in the OM. This investigation is the first to provide evidence that MAPK proteins are differentially activated at rest and in response to a bout of resistance exercise in skeletal muscle of young and old men. These findings may have implications for other processes (e.g. transcription and translation) involved in skeletal muscle type and growth, when examining the changes occurring with ageing muscle before and after resistance exercise/training.

Master athletes

Over the past 3 decades, there has been a continued increase in the number of "older" participants in sporting events such as running, swimming, cycling, rowing, and weightlifting. Some master athletes come from a background with years of training and competition experience, while others have only begun to compete as they approach middle-aged and older. The majority of what we currently know about master athletes and aging has been gained from both cross-sectional and longitudinal testing and re-testing master athletes and recreational athletes. The focus of this paper is on the physiological profile of athletes and individuals performing regular exercise training. Physiological data from elite and non-elite, recreational, sedentary, and senior athletes clearly indicate that human skeletal muscle has a high degree of plasticity that is maintained late into life. Muscle fiber protein expression and single muscle fiber contractile properties are greatly influenced by exercise training. It appears that skeletal muscle can quickly adapt to accommodate a wide range of functionality to meet the demands (or lack of demands) placed upon it.

Production of tissue plasminogen activator (t-PA) in Aspergillus niger

A protease-deficient strain of Aspergillus niger has been used as a host for the production of human tissue plasminogen activator (t-PA). In defined medium, up to 0.07 mg t-PA (g biomass)(-1) was produced in batch and fed-batch cultures and production was increased two- to threefold in two-phase batch cultures in which additional glucose was provided as a single pulse at the end of the first batch growth phase. Production was increased [up to 1.9 mg t-PA (g biomass)(-1)] by the addition of soy peptone to the defined medium. The rate of t-PA production in batch cultures supplemented with soy peptone (0.2 to 0.6 mg t-PA L(-1) h(-1)) was comparable to rates observed previously in high-producing mammalian or insect cell cultures. In glucose-limited chemostat culture supplemented with soy peptone, t-PA was produced at a rate of 0.7 mg t-PA L(-1) h(-1). Expression of t-PA in A. niger resulted in increased expression of genes (bipA, pdiA, and cypB) involved in the unfolded protein response (UPR). However, when cypB was overexpressed in a t-PA-producing strain, t-PA production was not increased. The t-PA produced in A. niger was cleaved into two chains of similar molecular weight to two-chain human melanoma t-PA. The two chains appeared to be stable for at least 16 h in culture supernatant of the host strain. However, in general, <1% of the t-PA produced in A. niger was active, and active t-PA disappeared from the culture supernatant during the stationary phase of batch cultures, suggesting that the two-chain t-PA may have been incorrectly processed or that initial proteolytic cleavage occurred within the proteolytic domain of the protein. Total t-PA (detected by enzyme-linked immunoassay) also eventually disappeared from culture supernatants, confirming significant extracellular proteolytic activity, even though the host strain was protease-deficient.

The effect of pH on glucoamylase production, glycosylation and chemostat evolution of Aspergillus niger

The effect of ambient pH on production and glycosylation of glucoamylase (GAM) and on the generation of a morphological mutant produced by Aspergillus niger strain B1 (a transformant containing an additional 20 copies of the homologous GAM glaA gene) was studied. We have shown that a change in the pH from 4 to 5.4 during continuous cultivation of the A. niger B1 strain instigates or accelerates the spontaneous generation of a morphological mutant (LB). This mutant strain produced approx. 50% less extracellular protein and GAM during both chemostat and batch cultivation compared to another strain with parental-type morphology (PS). The intracellular levels of GAM were also lower in the LB strain. In addition, cultivation of the original parent B1 strain in a batch-pulse bioreactor at pH 5.5 resulted in a 9-fold drop in GAM production and a 5-fold drop in extracellular protein compared to that obtained at pH 4. Glycosylation analysis of the glucoamylases purified from shake-flask cultivation showed that both principal forms of GAM secreted by the LB strain possessed enhanced galactosylation (2-fold), compared to those of the PS. Four diagnostic methods (immunostaining, mild methanolysis, mild acid hydrolysis and beta-galactofuranosidase digestion) provided evidence that the majority of this galactose was of the furanoic conformation. The GAMs produced during batch-pulse cultivation at pH 5.5 similarly showed an approx. 2-fold increase in galactofuranosylation compared to pH 4. Interestingly, in both cases the increased galactofuranosylation appears primarily restricted to the O-linked glycan component. Ambient pH therefore regulates both GAM production and influences its glycosylation.

Resistance training improves single muscle fiber contractile function in older women

The purpose of this study was to 1) examine single cell contractile mechanics of skeletal muscle before and after 12 wk of progressive resistance training (PRT) in older women (n = 7; 74 +/- 2 yr) and 2) to compare these results to our previously completed single cell PRT work with older men (n = 7; 74 +/- 2 yr) (Trappe S, Williamson D, Godard M, Porter D, Rowden G, and Costill D. J Applied Physiol 89:143--152, 2000). Knee extensor PRT was performed 3 days/wk at 80% of one-repetition maximum. Muscle biopsies were obtained from the vastus lateralis before and after the PRT. Chemically skinned single muscle fibers (n = 313) were studied at 15 degrees C for peak tension (P(o)), unloaded shortening velocity (V(o)), and power. Due to the low number of hybrid fibers identified post-PRT, direct comparisons were limited to MHC I and IIa fibers. Muscle fiber diameter increased 24% (90 +/- 2 to 112 +/- 6 microm; P < 0.05) in MHC I fibers with no change in MHC IIa fibers. P(o) increased (P < 0.05) 33% in MHC I (0.76 +/- 0.04 to 1.01 +/- 0.09 mN) and 14% in MHC IIa (0.73 +/- 0.04 to 0.83 +/- 0.05 mN) fibers. Muscle fiber V(o) was unaltered in both fiber types with PRT. MHC I and IIa fiber power increased (P < 0.05) 50% [11 +/- 2 to 17 +/- 2 microN. fiber length (FL). s(-1)] and 25% (40 +/- 8 to 51 +/- 6 microN. FL. s(-1)), respectively. However, when peak power was normalized to cell size, no pre- to postimprovements were observed. These data indicate that PRT in elderly women increases muscle cell size, strength, and peak power in both slow and fast muscle fibers, which was similar to the older men. However, in contrast to the older men, no change in fiber V(o) or normalized power was observed in the older women. These data suggest that older men and women respond differently at the muscle cell level to the same resistance-training stimulus.

Effect of swim taper on whole muscle and single muscle fiber contractile properties

PURPOSE

To examine the changes in whole muscle function and single cell contractile properties of Type I and II muscle fibers from the deltoid muscle of highly trained swimmers before and after a 21-d reduction in training volume (taper).

METHODS

Six college male swimmers (age, 20+/-1 yr; height, 187+/-2 cm, weight, 79+/-3 kg, fat, 7+/-1%) who had been, on average, swimming 6200 m x d(-1) for 5 months before the taper participated in this investigation.

RESULTS

Whole muscle power increased (P < 0.05) 17% and 13% on the swim bench and swim power tests, respectively. Swim times improved by 4% (range: 3.0-4.7%; P < 0.05). There was no change in Type I fiber diameter, whereas Type IIa fibers were 11% larger (P < 0.05) after taper. Peak force (Po) of the Type I fibers was unaffected by the taper but increased (P < 0.05) from 0.63+/-0.02 to 0.82+/-0.05 mN in the IIa fibers. However, the specific force (Po/CSA) of the IIa fibers was unchanged. Shortening velocity (Vo) was 32% and 67% faster (P < 0.05) in the Type I and IIa fibers, respectively. Although Type I fiber power was unaltered, the IIa fibers increased 2.5-fold from 24.6+/-2.8 to 56.2+/-3.9 microN x FL x s(-1). When power was normalized for cell size, the power was still elevated twofold.

CONCLUSIONS

These data suggest that tapering induces alterations in the contractile properties of single muscle fibers. Further, it appears that the Type IIa fibers are more affected than the Type I fibers by the taper. The increased size, strength, velocity, and power of the IIa fibers may be responsible for the improvements in whole muscle strength and power after the taper.

beta-hydroxy-beta-methylbutyrate (HMB) supplementation in humans is safe and may decrease cardiovascular risk factors

The leucine metabolite, beta-hydroxy-beta-methylbutyrate (HMB) enhances the effects of exercise on muscle size and strength. Although several reports in animals and humans indicate that HMB is safe, quantitative safety data in humans have not been reported definitively. The objective of this work was to summarize safety data collected in nine studies in which humans were fed 3 g HMB/d. The studies were from 3 to 8 wk in duration, included both males and females, young and old, exercising or nonexercising. Organ and tissue function was assessed by blood chemistry and hematology; subtle effects on emotional perception were measured with an emotional profile test (Circumplex), and tolerance of HMB was assessed with a battery of 32 health-related questions. HMB did not adversely affect any surrogate marker of tissue health and function. The Circumplex emotion profile indicated that HMB significantly decreased (improved) one indicator of negative mood (Unactivated Unpleasant Affect category, P < 0.05). No untoward effects of HMB were indicated. Compared with the placebo, HMB supplementation resulted in a net decrease in total cholesterol (5.8%, P < 0.03), a decrease in LDL cholesterol (7.3%, P < 0.01) and a decrease in systolic blood pressure (4.4 mm Hg, P < 0.05). These effects of HMB on surrogate markers of cardiovascular health could result in a decrease in the risk of heart attack and stroke. In conclusion, the objective data collected across nine experiments indicate that HMB can be taken safely as an ergogenic aid for exercise and that objective measures of health and perception of well-being are generally enhanced.

Effect of resistance training on single muscle fiber contractile function in older men

The purpose of this study was to examine single cell contractile mechanics of skeletal muscle before and after 12 wk of progressive resistance training (PRT) in older men (n = 7; age = 74 +/- 2 yr and weight = 75 +/- 5 kg). Knee extensor PRT was performed 3 days/wk at 80% of one-repetition maximum. Muscle biopsy samples were obtained from the vastus lateralis before and after PRT (pre- and post-PRT, respectively). For analysis, chemically skinned single muscle fibers were studied at 15 degrees C for peak tension [the maximal isometric force (P(o))], unloaded shortening velocity (V(o)), and force-velocity parameters. In this study, a total of 199 (89 pre- and 110 post-PRT) myosin heavy chain (MHC) I and 99 (55 pre- and 44 post-PRT) MHC IIa fibers were reported. Because of the minimal number of hybrid fibers identified post-PRT, direct comparisons were limited to MHC I and IIa fibers. Muscle fiber diameter increased 20% (83 +/- 1 to 100 +/- 1 microm) and 13% (86 +/- 1 to 97 +/- 2 microm) in MHC I and IIa fibers, respectively (P < 0.05). P(o) was higher (P < 0.05) in MHC I (0.58 +/- 0.02 to 0.90 +/- 0.02 mN) and IIa (0.68 +/- 0.02 to 0.85 +/- 0.03 mN) fibers. Muscle fiber V(o) was elevated 75% (MHC I) and 45% (MHC IIa) after PRT (P < 0.05). MHC I and IIa fiber power increased (P < 0.05) from 7.7 +/- 0.5 to 17.6 +/- 0.9 microN. fiber lengths. s(-1) and from 25.5 to 41.1 microN. fiber lengths. s(-1), respectively. These data indicate that PRT in elderly men increases muscle cell size, strength, contractile velocity, and power in both slow- and fast-twitch muscle fibers. However, it appears that these changes are more pronounced in the MHC I muscle fibers.