Gladys Onambele-Pearson

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.

Gender differences in fascicular lengthening during eccentric contractions: the role of the patella tendon stiffness

Elastic tendons have been suggested to attenuate fascicle lengthening during eccentric contractions; however, there is no in vivo evidence to support this hypothesis. Therefore, the aim of this study was to determine whether patella tendon stiffness modulates vastus lateralis (VL) fascicle lengthening during eccentric contractions in males and females.

A review of facial protective equipment use in sport and the impact on injury incidence

Sporting activities have an inherent risk of facial injury from traumatic impacts from fellow competitors, projectiles, and collisions with posts or the ground. This retrospective review systematically describes the interplay between the type of sport (including the level at which specific sports are played), the sex of the players and their musculoskeletal characteristics, the technology behind the materials used, the protective devices commonly used, the anatomical site, and the regularity of incidence of fractures. We describe how variations in sporting activities induce different orofacial fracture patterns, and critically consider the methods used to test protective headgear against more contemporary techniques. Facial injuries can have a profound psychological effect on those injured, can take a long time to heal, and have been known to end promising careers. Use of properly fitted protective head or facial equipment could reduce the number of facial fractures commonly seen in sports. We recommend that individual sports should have full risk assessments, and that mandatory standards should be agreed about protective devices that would be appropriate.

Effect of Foot and Ankle Immobilization on Leg and Thigh Muscles' Volume and Morphology: A Case Study Using Magnetic Resonance Imaging

Our aim was to determine the time course of any changes in muscle volume and shape in the lower limbs following immobilization. A healthy young woman (29 years) had suffered a fracture of the fifth metatarsal of the right foot. MRI scanning of her right thigh and calf muscles had been performed 1 month before the injury (Pre) during a scan initially planned as a teaching tool, 2 days following a 4‐week immobilization period (Post), and after a 2‐month recovery period (Post+2). The results show muscle volume decrements in the triceps surae (TS), quadriceps (Quad), and hamstring (Ham) of 21.9%, 24.1%, and 6.5%, respectively, between the Pre and Post measurements. At Post+2, the Quad and TS muscle volumes were still 5.2% and 9.5% lower, compared with the Pre data. The Ham muscle volume, however, was 2.7% greater than at the Pre phase. Following recovery, the increase in individual TS muscles volume was limited to both proximal and medial (with respect to the knee joint) segments of the muscles. These results indicate very substantial and rapid losses in muscle volumes, both proximally and distally to the immobilization site. The results also show that recovery is far from complete up to 2 months post cast removal. The results have implications for the requirements for rehabilitation for orthopedic patients. Anat Rec, 2008.

HRT affects skeletal muscle contractile characteristics: a definitive answer?

In this context, Ronkainen and colleagues (9) have cleverly used a design that minimizes the potential of genetic and/or physiological differences between users and nonusers (by using monozygotic twins), while optimizing the ability to tease out any HRT effects. The presented results are in favor of HRT having a significant positive impact on skeletal muscle functioning, given the strong relationship between muscle performance and HRT usage reported here. Through the robust design adopted here, this study therefore incrementally advances the field and in fact tips the balance toward a positive and measurable impact of HRT: HRT users have five times the levels of estrogen, walk 7% faster, jump 16% higher, and exhibit 8% greater relative lean tissue content and 5% smaller relative fatty tissue content compared with their nonusing counterparts.

Is there a morning-to-evening difference in the acute IL-6 and cortisol responses to resistance exercise?

Exercise training is known to induce a molecular adaptation process involving inflammatory responses. However any time-of-day effect of exercise on inflammatory responses remains unknown. The aim of the present study was to investigate whether acute bouts of intense exercise performed at different times of the day would affect the release Interleukin-6 (IL-6), one of the most abundant cytokines in mammalian endocrine response to exercise. Cortisol levels were measured as a confirmation of correct timing of exercise and to determine any impact it may have on the cytokine release. Twelve healthy male participants carried out 30 min of intense exercise (3 sets of 8-12 repetitions for 4 resistance exercises at 70% of 1RM) in morning (08:15-09:00 h), and evening (18:15-19:00 h) sessions. An 8h fasting period was required before each exercise session. Blood samples were taken immediately pre and post each exercise sessions to determine IL-6 and cortisol levels. Our data show that whilst the training group showed no post-exercise changes in serum_IL-6 levels (P>0.05), the control group on the other hand showed significant time-of-day modifications in serum_IL-6 levels (P=0.008). Moreover, a significant interaction between intervention phase (pre-post training, AM vs. PM) and group (Exercise vs. Control) is evidenced in terms of serum_IL-6 levels (P=0.014). This interaction however was nullified when the between group differences at baseline were partialled out in a covariate analysis (P>0.05). We also found that the main effect of experimental phase on Cortisol was present in both the trained (P=0.004) and control groups (p<0.001) with no significant interaction (P>0.05). Based on the current data, we would propose that exercise and/or time-of-day would not interfere with clinical endocrine profiling of IL-6 in a population.

The human patellar tendon moment arm assessed in vivo using dual-energy X-ray absorptiometry

Accurate assessment of muscle-tendon forces in vivo requires knowledge of the muscle-tendon moment arm. Dual-energy X-ray absorptiometry (DXA) can produce 2D images suitable for visualising both tendon and bone, thereby potentially allowing the moment arm to be measured but there is currently no validated DXA method for this purpose. The aims of this study were (i) to compare in vivo measurements of the patellar tendon moment arm (dPT) assessed from 2D DXA and magnetic resonance (MR) images and (ii) to compare the reliability of the two methods. Twelve healthy adults (mean ± SD: 31.4 ± 9.5 yr; 174.0 ± 9.5 cm; 76.2 ± 16.6 kg) underwent two DXA and two MR scans of the fully extended knee at rest. The tibiofemoral contact point (TFCP) was used as the centre of joint rotation in both techniques, and the dPT was defined as the perpendicular distance from the patellar tendon axis to the TFCP. The dPT was consistently longer when assessed via DXA compared to MRI (+3.79 ± 1.25 mm or +9.78 ± 3.31%; P<0.001). The test-retest reliability of the DXA [CV=2.13%; ICC=0.94; ratio limits of agreement (RLA)=1.01 (*/÷1.07)] and MR [(CV=2.27%; ICC=0.96; RLA=1.00 (*/÷1.07)] methods was very high and comparable between techniques. Moreover, the RLA between the mean DXA and MRI dPT values [1.097 (*/÷1.061)] demonstrated very strong agreement between the two methods. In conclusion, highly reproducible dPT measurements can be determined from DXA imaging with the knee fully extended at rest. This has implications for the calculation of patellar tendon forces in vivo where MR equipment is not available.

The manipulation of strain, when stress is controlled, modulates in vivo tendon mechanical properties but not systemic TGF-β1 levels

Modulators of loading‐induced in vivo adaptations in muscle–tendon complex (MTC) mechanical properties remain unclear. Similarly contentious, is whether changes in MTC characteristics are associated with growth factor levels. Four groups were subjected to varying magnitudes of stress/strain: Group 1 trained with the MTC at a shortened position (MTCS; n = 10); Group 2 at a lengthened position (MTCL; n = 11; stress levels matched to MTCS); Group 3 over a wide range of motion (MTCX; n = 11); and Group 4 (n = 10) was the control population (no training). Patella tendon Stiffness (P < 0.001), Youngs modulus, and quadriceps torque (P < 0.05) increments (only seen in the training groups), showed MTCL and MTCX groups responses to be superior to those of MTCS (P < 0.05). In addition, MTCL and MTCX better maintained adaptations compared to MTCS (P < 0.05) following detraining, with a pattern of slower loss of improvements at the early phase of detraining in all training groups. There were no significant changes (P > 0.05) in antagonist cocontraction, patella tendon dimensions or circulating transforming growth factor beta (TGF‐β1) levels following training or detraining in any of the groups. We conclude that chronically loading the MTC in a relatively lengthened position (which involves greater strains) enhances its mechanical properties, more so than loading in a shortened position. This is true even after normalizing for internal stress. The underlying endocrine mechanisms do not appear to be mediated via TGF‐β1, at least not at the systemic level. Our findings have implications with regard to the effectiveness of eccentric loading on improved tendon structural and mechanical properties.

The differential hormonal milieu of morning versus evening, may have an impact on muscle hypertrophic potential

Substantial gains in muscle strength and hypertrophy are clearly associated with the routine performance of resistance training. What is less evident is the optimal timing of the resistance training stimulus to elicit these significant functional and structural skeletal muscle changes. Therefore, this investigation determined the impact of a single bout of resistance training performed either in the morning or evening upon acute anabolic signalling (insulin-like growth factor-binding protein-3 (IGFBP-3), myogenic index and differentiation) and catabolic processes (cortisol). Twenty-four male participants (age 21.4±1.9yrs, mass 83.7±13.7kg) with no sustained resistance training experience were allocated to a resistance exercise group (REP). Sixteen of the 24 participants were randomly selected to perform an additional non-exercising control group (CP) protocol. REP performed two bouts of resistance exercise (80% 1RM) in the morning (AM: 0800 hrs) and evening (PM: 1800 hrs), with the sessions separated by a minimum of 72 hours. Venous blood was collected immediately prior to, and 5 min after, each resistance exercise and control sessions. Serum cortisol and IGFBP-3 levels, myogenic index, myotube width, were determined at each sampling period. All data are reported as mean ± SEM, statistical significance was set at P≤0.05. As expected a significant reduction in evening cortisol concentration was observed at pre (AM: 98.4±10.5, PM: 49.8±4.4 ng/ml, P<0.001) and post (AM: 98.0±9.0, PM: 52.7±6.0 ng/ml, P<0.001) exercise. Interestingly, individual cortisol differences pre vs post exercise indicate a time-of-day effect (AM difference: -2±2.6%, PM difference: 14.0±6.7%, P = 0.03). A time-of-day related elevation in serum IGFBP-3 (AM: 3274.9 ± 345.2, PM: 3605.1 ± 367.5, p = 0.032) was also evident. Pre exercise myogenic index (AM: 8.0±0.6%, PM: 16.8±1.1%) and myotube width (AM: 48.0±3.0, PM: 71.6±1.9 μm) were significantly elevated (P<0.001) in the evening. Post exercise myogenic index was greater AM (11.5±1.6%) compared with PM (4.6±0.9%). No difference was observed in myotube width (AM: 48.5±1.5, PM: 47.8±1.8 μm) (P>0.05). Timing of resistance training regimen in the evening appears to augment some markers of hypertrophic potential, with elevated IGFBP-3, suppressed cortisol and a superior cellular environment. Further investigation, to further elucidate the time course of peak anabolic signalling in morning vs evening training conditions, are timely.

Genetic Variation, Protein Composition and Potential Influences on Tendon Properties in Humans

Sequence variations in genes that code for proteins involved in homeostatic processes within tendons may influence tendon mechanical properties. Since variants of the four genes COL5A1, TNC, MMP3 and GDF5 have been implicated in the aetiopathogenesis of tendinopathies, which is ultimately characterised by abnormal structural and regulatory processes, sequence variations in these four genes may also influence how the tendon functions mechanically, even in the absence of tendinopathy. For example, two reports of association between variation in the COL5A1 gene and measures of flexibility complement reported associations between genotype and incidence of tendinopathy. Non-genetic factors such as age, body mass and physical activity status influence risk of tendon injury and physical performance potential independently from genomics, and also in gene-environment interactions. However, these non-genetic factors are often not considered in genetic association studies, probably due to their retrospective nature. Further research examining COL5A1, TNC, MMP3 and GDF5, as well as other genes that may influence the maintenance of tendon homeostasis such as COL1A1 which regulates the production of collagen type 1, the most abundant structural component of tendon is encouraged. Establishing the genetic basis of tendon properties in asymptomatic populations may advance understanding of some aspects relevant to physical performance and of the aetiology of tendinopathies. To improve understanding, accurate and reproducible assessments of tendon properties are required. However, no valid and reliable assessments of tendon properties, such as those involving in vivo ultrasound imaging techniques, have yet been applied to genetic association studies in humans.