The impact of obesity on skeletal muscle strength and structure through adolescence to old age.

Obesity is associated with functional limitations in muscle performance and increased likelihood of developing a functional disability such as mobility, strength, postural and dynamic balance limitations. The consensus is that obese individuals, regardless of age, have a greater absolute maximum muscle strength compared to non-obese persons, suggesting that increased adiposity acts as a chronic overload stimulus on the antigravity muscles (e.g., quadriceps and calf), thus increasing muscle size and strength. However, when maximum muscular strength is normalised to body mass, obese individuals appear weaker. This relative weakness may be caused by reduced mobility, neural adaptations and changes in muscle morphology. Discrepancies in the literature remain for maximal strength normalised to muscle mass (muscle quality) and can potentially be explained through accounting for the measurement protocol contributing to muscle strength capacity that need to be explored in more depth such as antagonist muscle co-activation, muscle architecture, a criterion valid measurement of muscle size and an accurate measurement of physical activity levels. Current evidence demonstrating the effect of obesity on muscle quality is limited. These factors not being recorded in some of the existing literature suggest a potential underestimation of muscle force either in terms of absolute force production or relative to muscle mass; thus the true effect of obesity upon skeletal muscle size, structure and function, including any interactions with ageing effects, remains to be elucidated

Whole-body and segmental analysis of body composition in adult males with achondroplasia using dual X-ray absorptiometry

© 2019 Sims et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Achondroplasia is a condition characterized by a genetic mutation affecting long bone endplate development. Current data suggests that the bone mineral content (BMC) and bone mineral density (BMD) of achondroplasic populations are below age matched individuals of average stature (controls). Due to the disproportionate limb-to-torso length compared to controls however, the lower BMC and BMD may be nullified when appropriately presented. The aim of this study was to measure whole-body and segmental body composition in adult males with achondroplasia (N = 10, 22 ±3 yrs), present data relative to whole-body and whole-limb values and compare all values to age matched controls (N = 17, 22 ±2 yrs). Dual X-ray absorptiometry (DEXA) was used to measure the in vivo mass of the whole-body and 15 segments, from which BMD, BMC, fat free mass (FFM) and body fat mass were measured. BMC of lumbar vertebrae (L1-4) was also measured and presented as a volumetric BMD (BMD VOL ). The achondroplasic group had less BMC, BMD and FFM, and more body fat mass than controls as a whole-body measure. The lower achondroplasic BMC and BMD was somewhat nullified when presented relative to whole-body and whole-limb values respectively. There was no difference in lumbar BMD VOL between groups. Whole-body BMD measures presented the achondroplasic group as ‘osteopenic’. When relative to whole-limb measures however, achondroplasic BMD descriptions were normal. Further work is needed to create a body composition database for achondroplasic population’s, or for clinicians to present achondroplasic body composition values relative to the whole-limb

Oral contraceptive pill use and the susceptibility to markers of exercise-induced muscle damage

© 2017, The Author(s). Purpose: Firstly, to establish whether oral contraceptive pill (OCP) users are more susceptible to muscle damage compared to non-users, and secondly, to establish whether differences can be attributed to differences in patella tendon properties. Methods: Nine female OCP users and 9 female non-users participated in the investigation. Combining dynamometry, electromyography and ultrasonography, patella tendon properties and vastus lateralis architectural properties were measured pre and during the first of 6 sets of 12 maximal voluntary eccentric knee extensions. Serum oestrogen levels were measured on the 7th day of the pill cycle and the 14th day of menstrual cycle in OCP users and non-users, respectively. Maximal voluntary isometric knee extension torque loss, creatine kinase and muscle soreness were measured 48 h pre-damage, post-damage, and 48, 96 and 168 h post-damage. Results: Oestrogen levels were significantly lower in OCP users compared to non-users (209 ± 115 and 433 ± 147 pg/ml, respectively, p = 0.004). Proposed determinants of muscle damage, patella tendon stiffness and maximal eccentric torque did not differ between OCP users and non-users. The change in creatine kinase from pre to peak was significantly higher in OCP users compared to non-users (962 ± 968 and 386 ± 474 Ul, respectively, p = 0.016). There were no other differences in markers of muscle damage. Conclusion: Although our findings suggest that, when compared to non-users, the OCP may augment the creatine kinase response following eccentric exercise, it does not increase the susceptibility to any other markers of muscle damage

Omega-3 fatty acids and vitamin D in immobilisation: Part B- modulation of muscle functional, vascular and activation profiles

Abstract Objectives: This study set out to determine whether two potential protein-sparing modulators (eicosapentaenoic acid and vitamin D) would modulate the anticipated muscle functional and related blood vessels function deleterious effects of immobilisation. Design: The study used a randomised, double-blind, placebo-controlled design. Setting: The study took part in a laboratory setting. Participants: Twenty-four male and female healthy participants, aged 23.0±5.8 years. Intervention: The non-dominant arm was immobilised in a sling for a period of nine waking hours a day over two continuous weeks. Participants were randomly assigned to one of three groups: placebo (n=8, Lecithin, 2400 mg daily), omega-3 (-3) fatty acids (n=8, eicosapentaenoic acid (EPA); 1770 mg, and docosahexaenoic acid (DHA); 390 mg DHA, daily) or vitamin D (n=8, 1,000 IU daily). Measurements: Isometric and isokinetic torque, antagonist muscle co-contraction (activation profile), muscle fatigability indices, and arterial resting blood flow were measured before, at the end of the immobilisation period, and two weeks after re-mobilisation. Results: Muscle elbow flexion and extension isometric and isokinetic torque decreased significantly with limb immobilisation in the placebo group (P0.05) towards attenuating the decreases observed in the placebo group. There was no significant change in muscle fatigue parameters or co-contraction values with immobilisation and no effect of supplementation group (P>0.05). Similarly, this immobilisation model had no impact on the assessed blood flow kinetics. All parameters had returned to baseline values at the re-mobilisation phase of the study. Conclusion: Overall, at the current doses, neither -3 nor vitamin D supplementation significantly attenuated declines in torque associated with immobilisation. It would appear that muscle function (described here in Part B) might not be as useful a marker of the effectiveness of a supplement against the impact of immobilisation compared to tissue composition changes (described in Part A)

Menstrual cycle variations in oestradiol and progesterone have no impact on in vivo medial gastrocnemius tendon mechanical properties

Background: Tendon tissue contains oestrogen receptors and is therefore likely to be responsive to female sex hormones. Here we examine any effect of levels of female sex hormones associated with the menstrual cycle phase on corresponding tendon mechanical properties. Methods: Fifteen healthy females aged 23 (SEM 1.0 years) underwent three assessments of medial gastrocnemius tendon mechanical properties. Assessments were carried out once during days 1–4, 12–14 and 20–23 (with day 1 being the first day of menstruation). Venous blood samples were taken on the same days as tendon properties assessments to quantify serum levels of oestradiol and progesterone. Findings: There was no significant difference in the stiffness of the medial gastrocnemius tendon over the course of the menstrual cycle (days 1–4, 65.08 (SEM 5.16 Nm m-1), days 12–14, 62.73 (SEM 5.82 Nm m-1), days 20–23, 66.74 (SEM 7.14 Nm m-1)). There were also no significant differences in tendon length and cross-sectional area which led to no significant differences in Young’s modulus values. No correlations were found between serum levels of oestradiol and/or progesterone and tendon stiffness and/or Young’s modulus. Interpretation: Acute fluctuations in female sex hormones have no significant effect on medial gastrocnemius tendon mechanical properties. In a context where studies are often limited to selecting only oral contraceptive-users as participants in order to minimise potential noise related to the anticipated effects of menstrual cycle hormones on physical performance, our findings provide the basis for enabling the pooling of female tendon data, regardless of the phase of the menstrual cycle of individual participant

Relaxin affects the in vivo mechanical properties of some but not all tendons in normally menstruating young females.

Background: Relaxin (hRLX) is a hormone reported to affect collagen synthesis. Its effects are also thought to be modulated by other sex hormones, including oestrogen, which has previously been found to be associated with altering in vivo tendon properties. There is thus a potential for hRLX to impact on collagen, which could result in tendon structural and mechanical properties being modified. Aims: The present study therefore aimed to determine any interaction between hRLX and tendon stiffness, in normally menstruating females (n = 12). Methods: Tendon properties were determined using a combination of dynamometry and B mode ultrasound, whilst serum hRLX levels were established by ELISA. Results: Serum hRLX level was seen to be negatively associated with patellar tendon stiffness (r = -0.56; p0.05), or with any of the two tendons CSA (p>0.05). Conclusion: In young, normally menstruating females, hRLX appears to have a significant effect on the patellar but not the gastrocnemius tendon stiffness. Where it has an affect, this appears to be on the intrinsic properties rather than on the dimensions of said tendon. Future work to elucidate the physiological cause for this selectivity in the impact of relaxin will be key to mapping the impact of the endocrine system on the phenotype of tendinous tissue

Polygenic Models Partially Predict Muscle Size and Strength but Not Low Muscle Mass in Older Women

BACKGROUND Heritability explains 45-82% of muscle mass and strength variation, yet polygenic models for muscle phenotypes in older women are scarce. Therefore, the objective of the present study was to (1) assess if total genotype predisposition score (GPS) for a set of polymorphisms differed between older women with low and high muscle mass, and (2) utilise a data-driven GPS (GPS) to predict the variance in muscle size and strength-related phenotypes. METHODS In three-hundred 60- to 91-year-old Caucasian women (70.7 ± 5.7 years), skeletal muscle mass, biceps brachii thickness, vastus lateralis anatomical cross-sectional area (VL), hand grip strength (HGS), and elbow flexion (MVC) and knee extension (MVC) maximum voluntary contraction were measured. Participants were classified as having low muscle mass if the skeletal muscle index (SMI) < 6.76 kg/m or relative skeletal muscle mass (%SMM) < 22.1%. Genotyping was completed for 24 single-nucleotide polymorphisms (SNPs). GPS was calculated from 23 SNPs and compared between the low and high muscle mass groups. A GPS was performed to identify the association of SNPs with other skeletal muscle phenotypes. RESULTS There was no significant difference in GPS between low and high muscle mass groups, irrespective of classification based on SMI or %SMM. The GPS model, using 23 selected SNPs, revealed that 13 SNPs were associated with at least one skeletal muscle phenotype: rs11549465 was associated with four phenotypes and, in descending number of phenotype associations, rs4341 with three; rs7460 and rs2070802 with two; and rs17421511, rs10783485, rs1800169, rs1801131, rs1537516, rs7832552, rs1805086, rs1800012, and rs9939609 with one phenotype. The GPS with age included as a predictor variable explained 1.7% variance of biceps brachii thickness, 12.5% of VL, 19.0% of HGS, 8.2% of MVC, and 9.6% of MVC. CONCLUSIONS In older women, GPS did not differ between low and high muscle mass groups. However, GPS was associated with muscle size and strength phenotypes. Further advancement of polygenic models to understand skeletal muscle function during ageing might become useful in targeting interventions towards older adults most likely to lose physical independence

Influence of exercise intensity in older persons with unchanged habitual nutritional intake: skeletal muscle and endocrine adaptations

Long-term adherence to training programmes is difficult to attain. Yet, the benefits of exercise to general health and well-being are undeniable. Any measure to demonstrate the minimum required exercise for maximal benefit to a person is a promising avenue towards increasing the uptake and adherence to physical activity for the general public. The purpose of this study was to compare the effects of two different intensities of resistance training in healthy older adults. We hypothesised that compared to high-intensity resistance exercise, relatively low training intensity could also improve in vivo markers of healthy physiologic and endocrine functions in previously sedentary older individuals. Thirty (out of a possible 34 recruited) older adults were randomly assigned to low (LowR, i.e. ∼40% one repetition maximum (1RM)) versus high-resistance training (HighR, i.e. ∼80% 1RM) for 12 weeks. Neither intervention significantly impacted upon body composition markers including: body mass index (BMI), waist/hip ratio and bioelectric impedance. Muscle strength data showed an advantage for the HighR protocol with 51 ± 4% and 22.4 ± 10.2% (P < 0.05) improvements in 1RM strength and bilateral knee extension torque, respectively, compared with 17 ± 1% and 10.3 ± 4.7% (P < 0.05) increments in 1RM strength and bilateral torque in the LowR group. Unilateral torque did not change significantly in either group. Quadriceps muscle thickness data also showed a significantly greater benefit of the HighR protocol (5.8 ± 2.6% increase) compared with the LowR protocol (no change). Functional ability tests, including Get-up-and-go (GUG), Standing from lying and the 6-min walk, showed changes of −11.6 ± 4.8%, −15.6% and 8.5 ± 1.7% (P < 0.05), respectively, in HighR compared with only one significant improvement in the LowR, namely a −10.8 ± 3% (P < 0.05) improvement in the GUG test. Overnight fasting serum levels of IGFBP-3 increased, NPY decreased and TNF-α decreased significantly in the LowR group. Serum levels of glucose increased and NPY decreased significantly in HighR. Circulating levels of I, IL-6 and IGF-1 did not change with either intervention. In vivo physiologic changes show functional advantages for older persons carrying out high-resistance training. At the endocrine level, such an advantage is not clear. In fact, in terms of changes in sera levels of fasting glucose, IGFBP-3 and TNF-α, there appears to be an advantage to carrying out the lower intensity exercises for the aged populations where endocrine adaptations are key