Muscle determinants of bone mass, geometry and strength in prepubertal girls

Purpose: The aim of this study was to compare the relative contribution of peak muscle force (isokinetic peak torque) with surrogate estimates of muscle force, including leg lean tissue mass (LTM) and vertical jump height (VJH), on bone mass, geometry and strength in healthy prepubertal girls (n = 103).

Methods: Total leg and FN BMC and leg LTM were measured by DXA; the hip strength analysis program was used to assess FN diameter, cross-sectional area (CSA) and section modulus (Z). Isokinetic peak torque of the knee extensors and flexors (60°·s-1) were used as direct measures of peak muscle force. VJH was measured as an estimate of neuromuscular function. Total leg length or femoral length was used as a surrogate measure of moment arm length.

Results: All estimates of muscle function, except VJH, were positively associated with leg BMC (r = 0.72 - 0.90) and FN BMC, geometry and strength (r = 0.35-0.65) (all, P < 0.001). Multiple linear regression analyses revealed that leg LTM and isokinetic peak torque were independently and equally predictive of leg BMC and FN BMC, bone geometry and strength, explaining 8 to 28% of the variance in each of the bone traits after accounting for moment arm length. When isokinetic peak torque was corrected for both leg LTM and moment arm length, it remained an independent predictor of BMC, CSA and Z, but only accounted for an additional 2 to 5% of the variance.

Conclusion: These data suggest that DXA-derived leg LTM can be used as a reasonable surrogate for isokinetic peak muscle forces when assessing bone strength in relation to muscular function in healthy pre-pubertal girls.

Association between changes in habitual physical activity and changes in bone density, muscle strength, and functional performance in elderly men and women

OBJECTIVES: To investigate the long-term effects of habitual physical activity on changes in musculoskeletal health, functional performance, and fracture risk in elderly men and women.

DESIGN: Ten-year prospective population-based study.

SETTING: Malmö-Sjöbo Prospective Study, Sweden.

PARTICIPANTS: Participants were 152 men and 206 women aged 50, 60, 70, and 80 who were followed for 10 years.

MEASUREMENTS: Distal radius bone mineral density (BMD) (single photon absorptiometry), upper limb muscle (grip) strength, balance, gait velocity, occupational and leisure-time activity, and fractures (interview-administered questionnaire) were reassessed after 10 years. Annual changes for all measures were compared between participants with varying habitual physical activity histories at baseline and follow-up: inactive–inactive (n=202), active–inactive (n=47), inactive–active (n=49), and active–active (n=60). Data for men and women were pooled, because there were no sex-by-activity group interactions. To detect possible differences in fracture incidence between the varying habitual activity groups, participants were classified into two activity groups based on their activity classification at baseline and follow-up: inactive:less active versus active:more active.

RESULTS: The annual rate of bone loss was 0.6% per year less in individuals classified as active at both time points than in those classified as inactive at both time points (P<.01). Similar results were observed for balance, but there was no effect of varying habitual activity on changes in muscle strength or gait velocity. There were also no differences in fracture incidence between individuals categorized as active:more active and those categorized as inactive:less active during the follow-up (adjusted hazard ratio=0.90, 95% confidence interval (CI)=0.42–1.90).

CONCLUSION: This study showed that elderly men and women who maintained a habitually active lifestyle over 10 years had lower bone loss and retained better balance than those who remained habitually inactive.

Independent and combined effects of exercise and vitamin D on muscle morphology, function and falls in the elderly

Regular exercise, particularly progressive resistance training (PRT), is recognized as one of the most effective strategies to prevent age-related muscle loss (sarcopenia), but its effects on muscle function are mixed. However, emerging data indicates that high velocity PRT (fast concentric muscle contractions) is more effective for improving functional outcomes than traditional PRT. In terms of falls prevention, high-challenging balance training programs appear to be most effective. There is also compelling evidence that supplemental vitamin D is an effective therapeutic option for falls prevention. The findings from a recent meta-analysis revealed that supplemental vitamin D at a dose of at least 700–1,000 IU/d or an achieved serum 25(OH)D level of at least 60 nmol/L was associated with reduced falls risk among older individuals. Based on these findings, it is possible that the combination of exercise and vitamin D could have a synergistic effect on muscle morphology and function, particularly since both interventions have been shown to have beneficial effects on type II “fast twitch” muscle fibers and systemic inflammation, which have both been linked to losses in muscle mass and function. Unfortunately however, the findings from the limited number of factorial 2 × 2 design RCTs indicate that additional vitamin D does not enhance the effects of exercise on measures of muscle morphology, function or falls risk. However, none of these trials were adequately powered to detect a “synergistic” effect between the two treatment strategies, but it is likely that if an exercise-by-vitamin D interaction does exist, it may be limited to situations when vitamin D deficiency/insufficiency is corrected. Further targeted research in “high risk” groups is still needed to address this question, and evaluate whether there is a threshold level of serum 25(OH)D to maximize the effects of exercise on muscle and falls risk.

Altered movement patterns but not muscle recruitment in moderately trained triathletes during running after cycling

Previous studies have shown that cycling can directly influence neuromuscular control during subsequent running in some highly trained triathletes, despite these triathletes' years of practice of the cycle-run transition. The aim of this study was to determine whether cycling has the same direct influence on neuromuscular control during running in moderately trained triathletes. Fifteen moderately trained triathletes participated. Kinematics of the pelvis and lower limbs and recruitment of 11 leg and thigh muscles were compared between a control run (no prior exercise) and a 30 min run that was preceded by a 15 min cycle (transition run). Muscle recruitment was different between control and transition runs in only one of 15 triathletes (<7%). Changes in joint position (mean difference of 3°) were evident in five triathletes, which persisted beyond 5 min of running in one triathlete. Our findings suggest that some moderately trained triathletes have difficulty reproducing their pre-cycling movement patterns for running initially after cycling, but cycling appears to have little influence on running muscle recruitment in moderately trained triathletes.

NUCLEIC ACID EXPRESSED IN THE HYPOTHALAMUS OR MUSCLE TISSUE IN OBESE ANIMALS

An isolated nucleic acid molecule comprising a sequence of nucleotides encoding or complimentary to a sequence encoding a molecule or derivative or homologue thereof wherein said nucleic acid molecule is expressed in a large r amount in one or both hypothalamus tissue or muscle tissue of obese animals compared to lean animals or in fed animals compared to fasted animals. Nucle ic acid sequences are disclosed. It is proposed to use the expression products of such nucleic acids as modulators and/or monitors of physiological processes associated with obesity, anorexia, weight maintenance, impaired muscle development, diabetes and/or metabolic energy levels.

Nucleic acid expressed in hypothalamus or muscle tissue in obese animals

An isolated nucleic acid molecule comprising a sequence of nucleotides encoding or complimentary to a sequence encoding a molecule or derivative or homologue thereof wherein said nucleic acid molecule is expressed in a larger amount in one or both hypothalamus tissue or muscle tissue of obese animals compared to lean animals or in fed animals compared to fasted animals. Nucleic acid sequences are disclosed. It is proposed to use the expression products of such nucleic acids as modulators and/or monitors of physiological processes associated with obesity, anorexia, weight maintenance, impaired muscle development, diabetes and/or metabolic energy levels.

NUCLEIC ACID EXPRESSED IN THE HYPOTHALAMUS OR MUSCLE TISSUE IN OBESE ANIMALS

An isolated nucleic acid molecule comprising a sequence of nucleotides encoding or complimentary to a sequence encoding a molecule or derivative or homologue thereof wherein said nucleic acid molecule is expressed in a larger amount in one or both hypothalamus tissue or muscle tissue of obese animals compared to lean animals or in fed animals compared to fasted animals. Nucleic acid sequences are disclosed. It is proposed to use the expression products of such nucleic acids as modulators and/or monitors of physiological processes associated with obesity, anorexia, weight maintenance, impaired muscle development, diabetes and/or metabolic energy levels.

NUCLEIC ACID EXPRESSED IN THE HYPOTHALAMUS OR MUSCLE TISSUE IN OBESE ANIMALS

An isolated nucleic acid molecule comprising a sequence of nucleotides encoding or complimentary to a sequence encoding a molecule or derivative or homologue thereof wherein said nucleic acid molecule is expressed in a larger amount in one or both hypothalamus tissue or muscle tissue of obese animals compared to lean animals or in fed animals compared to fasted animals. Nucleic acid sequences are disclosed. It is proposed to use the expression products of such nucleic acids as modulators and/or monitors of physiological processes associated with obesity, anorexia, weight maintenance, impaired muscle development, diabetes and/or metabolic energy levels.

Innervation zone shift at different levels of isometric contraction in the biceps brachii muscle

Experiments were carried out to examine whether innervation zone (IZ) location remains stable at different levels of isometric contraction in the biceps brachii muscle (BB), and to determine how the proximity of the IZ affects common surface electromyography (sEMG) parameters. Twelve subjects performed maximal (MVC) and submaximal voluntary isometric contractions at 10%, 20%, 30%, 40%, 50% and 75% of MVC. sEMG signals were recorded with a 13 rows  5 columns grid of electrodes from the short head of BB. The IZ shifted in the proximal direction by up to 2.4 cm, depending upon the subject and electrode column. The mean shift of all the columns was 0.6 ± 0.4 cm (10% vs. 100% MVC, P < 0.001). This shift biased the average values of mean frequency (+21.8 ± 9.9 Hz, P < 0.001), root mean square (0.16 ± 0.15 mV, P < 0.05) and conduction velocity (1.15 ± 0.93 m/s, P < 0.01) in the channels immediately proximal to the IZ. The shift in IZ could be explained by shortening of the muscle fibers, and thus lengthening of the (distal) tendon due to increasing force. These results underline the importance of individual investigation of IZ locations before the placement of sEMG electrodes, even in isometric contractions.

Anabolic signalling in skeletal muscle : impact of diet and disease

This thesis examines the role of dietary proteins on the maintenance of skeletal muscle mass in men who may or may not be insulin-resistant. It identified that dairy foods are powerful stimulators of muscle growth however this response is reduced during insulin-resistance.

Body image, weight loss and muscle building among Tongan adolescents in Tonga and New Zealand

This study examined body image and associated behaviours among 48 adolescents (24 males, 24 females) in Tonga, as well as 48 Tongan adolescents (24 males, 24 females) living in New Zealand (NZ). There was a lack of focus on body weight and shape among adolescents in both countries. Males evidenced a high focus on muscles. Females wanted to lose weight and obtain a soft round body. There were very few differences in the body image or body change strategies of Tongan adolescents in Tonga or NZ. Sociocultural messages need to be explored further in order to better understand these findings.