Absolute Muscle Strength Research Articles

Adiposity Alters Muscle Strength and Size Responses to Resistance Training in Healthy Men and Women

2386 PURPOSE: The influence of adiposity on muscle strength and size responses to resistance training (RT) is unclear. We compared changes in biceps strength and size of the non-dominant arm in response to RT between normal weight (NW) and overweight (OW) healthy adults. METHODS: Subjects were 140 NW (mean ± SEM) (22.1 ± 0.2 kg/m2, 24.1 ± 0.4 yr) and 81 OW (29.0 ± 0.5 kg/m2, 26.1 ± 0.7 yr) Caucasian men (n = 89) and women (n = 132) who had not performed RT for 1 yr. Subjects underwent 12 wk (2 d/wk) of RT on the non-dominant arm. Biceps muscle strength (kg) was assessed by 1 repetition maximum (1RM) using the single arm curl. Biceps muscle cross sectional area (cm2) was measured using magnetic resonance imaging. Multivariate ANOVA was used to detect differences in muscle strength and size alterations between NW and OW groups. RESULTS: OW volunteers had greater pre-RT absolute biceps strength (10.2 ± 0.3 vs 8.9 ± 0.2kg) and size (20.56 ± 0.42 vs 17.40 ± 0.33cm2) than NW volunteers (p<0.05). Similarly, OW had greater post-RT absolute biceps strength (14.0 ± 0.3 vs 12.8 ± 0.3kg) and size measures (24.27 ± 0.50 vs 20.78 ± 0.39 cm2) than NW subjects, respectively (p<0.05). In contrast, when allometric scaling was applied, NW had greater pre- to post- RT muscle strength gains than OW, 0.31 ± 0.01 vs 0.25 ± 0.01 kg·kg-0.67, respectively (p<0.05). Adjusting muscle size changes for initial values, NW persons tended to have larger pre- to post- RT gains than OW persons, 19.6 ± 0.8 vs 17.9 ± 1.1%, respectively, but these differences did not achieve statistical significance (p≥0.05). CONCLUSION: OW subjects had greater pre- and post- RT absolute muscle strength and size as a result of RT than NW subjects; however, NW experienced greater gains in muscle strength and size than the OW when these responses were adjusted for body weight and initial values, respectively. Our findings suggest excess overall adiposity may attenuate the muscle strength and size responses to RT in apparently healthy, young men and women. Supported by NIH – NINDS RO1 NS40606-02

Functional improvement of dystrophic muscle by myostatin blockade.

Mice and cattle with mutations in the myostatin (GDF8) gene show a marked increase in body weight and muscle mass, indicating that this new member of the TGF-beta superfamily is a negative regulator of skeletal muscle growth. Inhibition of the myostatin gene product is predicted to increase muscle mass and improve the disease phenotype in a variety of primary and secondary myopathies. We tested the ability of inhibition of myostatin in vivo to ameliorate the dystrophic phenotype in the mdx mouse model of Duchenne muscular dystrophy (DMD). Blockade of endogenous myostatin by using intraperitoneal injections of blocking antibodies for three months resulted in an increase in body weight, muscle mass, muscle size and absolute muscle strength in mdx mouse muscle along with a significant decrease in muscle degeneration and concentrations of serum creatine kinase. The functional improvement of dystrophic muscle by myostatin blockade provides a novel, pharmacological strategy for treatment of diseases associated with muscle wasting such as DMD, and circumvents the major problems associated with conventional gene therapy in these disorders.

Morphological and histochemical studies of the genioglossus muscle.

The purpose of this preliminary study was to assess the histo-anatomic composition of the genioglossus muscle fibers. The genioglossus muscles were obtained from 4 cadavers and 1 autopsy specimen. On morphological study, the average diameters of the muscle fibers were seen to gradually increase, from the fibers that ran anteriorly to the dorsum of the tongue, to the fibers that ran posteriorly to the root of the tongue. Histochemical study revealed that type II fibers were significantly predominant in the anterior portion; there was no dominant fiber type in the posterior portion. Gradual changes in diameter were independent of fiber type. These findings may suggest that the fibers of the anterior portion are suitable for phasic action, and that the posterior is relatively tonic; and the posterior has larger absolute muscle strength than the anterior. It is thought that the fibers of the posterior portion might contribute to the maintenance of the mesopharyngeal airway and to vowel production, and that the anterior fibers might contribute to some fine movements and to consonant production.

Muscle strength and hormonal levels in adolescents: gender related differences.

The purpose of the present investigation was to study muscle strength in adolescents and its relationship to serum levels of testosterone and growth hormone in both genders. Thirty active adolescents (15 boys; age range 11 -12 y/o) participated in the first study. Isokinetic muscle strength of the dominant knee extensors (KE) was determined at 0, 12, 20, 30, 120, 180 and 240 deg/sec using a Cybex 340 dynamometer. The assessment of pubertal status was accomplished using the criteria of Tanner. Serum levels of total testosterone (T) and growth hormone (GH) were determined using radioimmunoassay techniques. Boys had higher (p< 0.001) T levels but no differences in muscle strength were detected between genders. Fifty-seven additional subjects representing three age groups (11-12 y/o, n=18; 13-14, n=21; 17-18, n=18) participated in the second study. A significant increase in peak torque (absolute and corrected for body weight) with age was observed in both genders. There were no significant gender differences in strength for the two youngest age groups, but boys were stronger than girls in the oldest age group (group 3). Testosterone and GH levels increased with age in boys but not in girls. Gender related differences in T were found in groups 2 and 3. A positive correlation (r=0,64 boys; r=0.46 girls) between testosterone levels and absolute muscle strength was seen in both genders. Our results suggest that increases in anabolic hormones precede muscle strength gains in adolescent males. In addition, gender related differences in muscle strength during adolescents cannot be explained solely on the basis of difference in body size or T levels.

A new concept for isokinetic hamstring: quadriceps muscle strength ratio.

Conventionally, the hamstring:quadriceps strength ratio is calculated by dividing the maximal knee flexor (hamstring) moment by the maximal knee extensor (quadriceps) moment measured at identical angular velocity and contraction mode. The agonist-antagonist strength relationship for knee extension and flexion may, however, be better described by the more functional ratios of eccentric hamstring to concentric quadriceps moments (extension), and concentric hamstring to eccentric quadriceps moments (flexion). We compared functional and conventional isokinetic hamstring: quadriceps strength ratios and examined their relation to knee joint angle and joint angular velocity. Peak and angle-specific (50 degrees, 40 degrees, and 30 degrees of knee flexion) moments were determined during maximal concentric and eccentric muscle contractions (10 degrees to 90 degrees of motion; 30 and 240 deg/sec). Across movement speeds and contraction modes the functional ratios for different moments varied between 0.3 and 1.0 (peak and 50 degrees), 0.4 and 1.1 (40 degrees), and 0.4 and 1.4 (30 degrees). In contrast, conventional hamstring:quadriceps ratios were 0.5 to 0.6 based on peak and 50 degrees moments, 0.6 to 0.7 based on 40 degrees moment, and 0.6 to 0.8 based on 30 degrees moment. The functional hamstring:quadriceps ratio for fast knee extension yielded a 1:1 relationship, which increased with extended knee joint position, indicating a significant capacity of the hamstring muscles to provide dynamic knee joint stability in these conditions. The evaluation of knee joint function by use of isokinetic dynamometry should comprise data on functional and conventional hamstring:quadriceps ratios as well as data on absolute muscle strength.

Bone Mineral and Muscle Strength Characteristics in Children with Turner Syndrome

Absolute total body (TB) and regional spine (RS) bone mineral content (BMC) measured by dual photon absorptiometry were lower (p &lt; .05) in Turner syndrome (TS) girls compared to a cohort of younger (by 2 years) but taller and heavier prepubertal girls. Maximal voluntary strength (MVC) of the elbow flexors, knee extensors, and plantar flexors were also consistently and, in most cases, significantly lower in TS girls. Differences between groups in absolute bone mineral and muscle strength disappeared, however, when normalized for skeletal cross-sectional area (areal density) and for the product of muscle cross-sectional area and estimated moment arm, respectively. Maximal voluntary strength and body mass correlated moderately strongly with the bone mineral measures, but only body mass contributed significantly to the variance in total body and regional spine bone mineral measures. Bone mineral and muscle strength appear appropriate for body size and for skeletal and muscle morphology in young TS girls.

Isometric and isokinetic muscle strength, anthropometry and physical activity in 8 and 13 year old Swedish children.

Isometric muscle strength of the hand-grip and of trunk flexion and extension, and isokinetic torque of elbow and knee flexion and knee extension were assessed in a random sample of 8 and 13 year old Swedish children. The results were compared with respect to sex and age in absolute terms and relative to weight, height2 and estimates of lean body mass and cross-sectional muscle area. Daily physical activity was also estimated. The muscle strength variables were in general found to be very similar in the 8 year old boys and girls. In the 13 year old group the boys were generally stronger than the girls, in both absolute and relative terms, except for similar torque values during knee extension. The absolute and relative muscle strength and torque values were higher in the older than in the younger children, with the exception of trunk strength per unit of body weight and of lean body mass, which were similar in boys of both ages and significantly lower in the older than in the younger girls. No significant correlation was found between the estimates of physical activity and isometric and isokinetic muscle strength and torque.

絶対筋力におよぼす静的および動的筋力トレーニングの影響

The purpose of this study was to observe the difference of training effect on the absolute muscle strength between static and dynamic strength training. The subjects were 14 adult males of whom 7 were exposed to static training and others to dynamic training. All subjects were trained every day for 12 weeks except Sundays. Training intensity was two-thirds of maximum isometric strength in static training group (S-group) and two-thirds of one repetition maximum (1RM) in dynamic training group (D-group). In S-group muscle strength was exerted statically for 1O seconds on the right angle of the elbow joint. In D-group the elbow joint was flexed between 75 and 105 degrees of the angle of elbow joint with the rhythm of one repetition in two seconds using audiovisual metronome, and it was repeated five times in a set. All training exercises for both groups were given three sets in a day. The cross-sectional area of elbow flexor muscle was measured at the extended position of the elbow joint before and after training by means of ultrasonic method, and the absolute muscle strength was calculated. The results were as follows: 1)Maximum isometric strength significantly increased (p < 0.001) by 25.9±4.2% (mean ± standard error) in S-group and 30.7±3.8% in D-group. No significant difference of strength increase was observed between dynamic and static training group. 2)The dynamic strength, measured as 1RM significantly increased (p < 0.001) by 22.7±1.1% in S-group and by 33.1±4.0% in D-group. The increase of 1RM in D-group was significantly higher than that in S-group. 3)1RM was about 70% of isometric maximum strength, which value was not affected by both training programs. 4)Cross-sectional area of muscle increased significantly by 5.4±1.4% (p < 0.01) in S-group and 3.2±1.3% (p < 0.05) in D-group. No significant difference in increase of muscle area was observed between S- and D-group. 5)Absolute muscle strength increased by training up to about 9.7kg/cm^2 (muscle area measured at extended position of elbow joint) in both training groups.