The Trp64Arg Polymorphism of the β3‐Adrenergic Receptor Gene Is Not Associated with Training‐Induced Changes in Body Composition: The HERITAGE Family Study

Objective: To investigate the association between the Trp64Arg polymorphism of the β3‐adrenergic receptor gene and changes in body composition in response to endurance training. Research Methods and Procedures: Adult sedentary white and black subjects participating in the HERITAGE Family Study were measured before and after 20 weeks on endurance training for the body mass index, fat mass, percentage of body fat, fat‐free mass, sum of eight skinfolds, and subcutaneous, visceral, and total abdominal fat areas. The association between the Trp64Arg polymorphism and the response phenotypes, computed as the difference between pre‐ and post‐training values, was tested by analysis of covariance separately in men and women. The gene by race interaction term was also tested. Results: No race differences were observed for allelic and genotype frequencies. Training resulted in significant reduction of body fat in both men and women. No association of the Trp64Arg polymorphism was observed with training‐induced changes for any of the body composition phenotypes in both men and women. Discussion: These results suggest that the Trp64Arg polymorphism of the β3‐adrenergic receptor gene is not related to changes in body composition in response to exercise training.     

Enthalpy efficiency of the soleus muscle contributes to improvements in running economy

During human running, the soleus, as the main plantar flexor muscle, generates the majority of the mechanical work through active shortening. The fraction of chemical energy that is converted into muscular work (enthalpy efficiency) depends on the muscle shortening velocity. Here, we investigated the soleus muscle fascicle behaviour during running with respect to the enthalpy efficiency as a mechanism that could contribute to improvements in running economy after exercise-induced increases of plantar flexor strength and Achilles tendon (AT) stiffness. Using a controlled longitudinal study design (n = 23) featuring a specific 14-week muscle–tendon training, increases in muscle strength (10%) and tendon stiffness (31%) and reduced metabolic cost of running (4%) were found only in the intervention group (n = 13, p < 0.05). Following training, the soleus fascicles operated at higher enthalpy efficiency during the phase of muscle–tendon unit (MTU) lengthening (15%) and in average over stance (7%, p < 0.05). Thus, improvements in energetic cost following increases in plantar flexor strength and AT stiffness seem attributed to increased enthalpy efficiency of the operating soleus muscle. The results further imply that the soleus energy production in the first part of stance, when the MTU is lengthening, may be crucial for the overall metabolic energy cost of running.     

Normative data for strength and flexibility of women throughout life

Previously established normative data for muscular strength, endurance and the flexibility of women have recently been criticized as being unreliable. Furthermore, no normative data for the muscular fitness of women over 70 years of age are established. The purpose of this study was to derive normative data for muscular fitness in women 20–70+ years old, and to compare these data to the most recently published norms of the American College of Sports Medicine (ACSM). A total of 304 independent-living women were evaluated for maximal performance of bench press, leg press, modified push-ups, grip strength, and sit-and-reach. Tables of normative values for each measurement were generated along with percentile rankings. Large discrepancies were found between these new data and those of the ACSM norms. Bench press norms from ACSM are comparatively high so that the average woman in this current sample scored below the 10th percentile of the ACSM rankings. Similarly, the average woman in our sample ranked in either the poor or fair category of the ACSM norms for modified push-ups, and in the poor ACSM category for sit-and-reach. In contrast, leg press scores for the average woman in this study fell within the good or excellent category of the ACSM norms, suggesting that the ACSM norms are too low. Grip strength for the middle-aged women in this study was higher than that in previous norms. These newly established norms are better suited for interpreting women's fitness test results than previously published norms. Accepted: 12 December 1997     

Fatigue- and training-related changes in ‘beta’ intermuscular interactions between agonist muscles

The synchronous activation of the muscles involved in force production is crucial for the neuromuscular performance, but the underlying mechanisms remain to be fully elucidated. Our aim was thus to contribute to understand the mechanisms involved in the synergistic activation of agonist muscles. Through wavelet-based time–frequency analysis, this study investigated the modulation of ‘beta’ intermuscular interactions (IM) during maximum isometric knee extensions performed before and after repetitive submaximal fatiguing contractions. Three groups of participants were included: 9 untrained subjects (control group, CO), 10 elite rugby league players (strength-trained group, ST) and 7 trail runners (endurance-trained group, ED), engaged for 5+ years in intense strength and endurance training, respectively. Before fatigue, CO showed higher IM when compared to ED, and a trend to higher IM when compared to ST. Following fatiguing contractions, all groups showed a decline in neuromuscular performance concomitant with a change (decline) in IM values for CO only. No differences were found between ST and ED regarding to IM either before or after fatiguing contractions. These findings suggested both a form of optimization of intermuscular coupling in trained individuals and the functional importance of intermuscular coupling as a mechanism responsible for the maintenance of the neuromuscular performance.     

State-dependent male mating tactics in the grey seal: the importance of body size

The purpose of this study was to examine the importance of bodysize and body composition as determinants of conditional matingtactics exhibited in male grey seals. We combined behavioralobservations with measures of energy expenditure and successon 42 known-age individuals during the breeding seasons of 1997–2001at Sable Island, Canada. Males with a large body mass arrivedat the breeding grounds with more body fat and body energy andcatabolized less body protein than smaller males. Males consumed1.9 ± 0.2 MJ day^–1, and those with a smaller percentageof body fat had higher rates of food energy intake. The amountof body energy on arrival was positively correlated with theduration of the breeding period. Males that exhibited the primarymating tactic of consortship were heavier, had absolutely morebody fat and body energy, and sustained breeding longer thanthose males that did not exhibit the primary tactic. Amongstall males, body mass showed a quadratic relationship with thenumber of female consorts mated and the estimated number ofpups sired. Thus, intermediate-sized males mated with the mostconsorts and achieved the highest success. Intermediate bodysize may be optimal during breeding due to greater agility inmale combat. Body size was an important determinant of matingtactics used by male grey seals. A large body size providedan energetic advantage of greater endurance while an intermediatebody size may provide greater competitive ability in acquiringconsortships.     

Physiological Performance and Stream Microhabitat use by the Centrarchids Lepomis megalotis and Lepomis macrochirus

Two centrarchids, Lepomis megalotis and L. macrochirus, were compared in laboratory studies of prey capture success, swimming endurance, morphology, hydrodynamic drag, and thermal tolerance, as well as field observations of focal point velocity and depth. For both species, capture of planktonic prey declined as current velocity increased, but L. megalotis was more efficient than L. macrochirus at higher current velocities. Capture of floating prey was not influenced by current velocity, but L. megalotis was more efficient overall at all velocities. Of the two species, L. megalotis was significantly more streamlined, had relatively lower hydrodynamic drag, and had higher swimming endurance in current. Both species had significantly higher critical thermal maxima (CTMax) in summer than in winter, but variance in CTMax was greater for L. megalotis than for L. macrochirus in both summer and winter. Differences between L. megalotis and L. macrochirus in performance and morphology may have direct influence on their relative abundances in small streams. Field observations showed L. megalotis was more common than L. macrochirus in faster, shallower microhabitats.     

Glycogen phosphorylase is involved in stress endurance and biofilm formation in Azospirillum brasilense Sp7

Here we report the identification of a glycogen phosphorylase ( glgP ) gene in the plant growth-promoting rhizobacterium Azospirillum brasilense , Sp7, and the characterization of a glgP marker exchange mutant of this strain. The glgP mutant showed a twofold reduction of glycogen phosphorylase activity and an increased glycogen accumulation as compared with wild-type Sp7, indicating that the identified gene indeed encodes a protein with glycogen phosphorylase activity. Interestingly, the glgP mutant had higher survival rates than the wild type after exposure to starvation, desiccation and osmotic pressure. The mutant was shown to be compromised in its biofilm formation ability. Analysis of the exopolysaccharide sugar composition of the glgP mutant revealed a decrease in the amount of glucose, accompanied by increases in rhamnose, fucose and ribose, as compared with the Sp7 exopolysaccharide. To the best of our knowledge, this is the first study that demonstrates GlgP activity in A. brasilense , and shows that glycogen accumulation may play an important role in the stress endurance of this bacterium.     

Isometric strength and occupational muscle disorders

In two longitudinal studies, initial muscle strength and endurance of the shoulder-forearm muscles were related to deterioration of shoulder-neck-arm disorders after one year. Group I (n = 32) worked in the automobile industry assembling car motors. Their work was performed when standing and walking, and implied varied postures and exertion of external forces. Group II (n = 96) worked in the electronics industry assembling printed circuit boards. They worked sitting down and were exposed mainly to postural static loads. Muscle strength was negatively related to deterioration in group I but no such relationship was found in group II. The mechanism of occupational muscular injury is discussed, and it is suggested that mechanical overstress of the musculoskeletal system causes injury in occupations where external forces are exerted. The mechanism of injury in static, postural loads remains to be explained.