Allometric scaling of isometric biceps strength in adult females and the effect of body mass index

The purposes of this study were to (1) derive and test allometric scaling models of biceps isometric strength using body mass (BM) and muscle cross-sectional area (CSA) as the scaling variables, (2) assess the influence of body mass index (BMI) by separating the cohort by BMI (normal <25 kg/m² vs. overweight/obese ≥25 kg/m²) and repeating step 1, and (3) assess the effect of BMI on isometric strength allometrically adjusted for differences in CSA by comparing scaled strength between normal weight versus overweight/obese women. The participants were 183 women (18–39 years old) who reported no strength training in the prior year. Isometric strength and CSA of the biceps were assessed on the non-dominant arm. The CSA allometric model met all statistical criteria and produced a scaling exponent of 0.44. The BM model did not meet these criteria until the entire cohort was separated by BMI. The scaling exponents for normal weight and overweight/obese women were 1.48 and 0.35, respectively. These data suggest that BMI exerted an influence on the relationship between BM and allometrically scaled isometric strength and may be explained by previous studies demonstrating greater contribution of fat mass (FM) versus fat-free mass (FFM) to BMI in overweight/obese women. As such, allometric scaling models of isometric strength, especially in populations that are heterogeneous with regard to body composition, must be carefully tested and examined across the range of BMI. Isometric strength relative to CSA was not significantly different between groups. However, allometrically scaled strength, using CSA as the criterion variable, was significantly greater in overweight/obese women compared to those of normal weight. These data suggest that isometric strength in women is not completely determined by CSA and other factors such as intramuscular fat and muscle fiber type may be confounding or contributing factors.     

Changes in body fat percentage during body weight stable conditions of increased daily protein intake vs. control

Objective

The objective of this study was to examine if increased protein intake vs. control influences body fat percentage during stable body weight.

Design

Body composition was assessed before and after a 3-month isoenergetic dietary intervention of 2MJ/d supplements exchanged with 2MJ/d of habitual ad libitum energy intake. The parallel design consisted of protein-rich supplements in the protein group (n = 12) and an isoenergetic combination of carbohydrate and fat supplements in the control group (n = 12). Daily protein intake was calculated from a 24 h urinary nitrogen. Body composition was measured by a combination of underwater-weighing technique, deuterium-dilution technique and whole-body dual-energy X-ray absorptiometry (DXA), a method that allows for estimation of 4-body compartments (fat and lean; water, bone and rest).

Results

Subjects were weight stable and did not change their habitual physical activity. Daily protein intake increased in the protein group during the intervention compared to baseline with + 11 ± 14 g (P < 0.05) vs. the control group that did not change their protein intake − 1 ± 15 g. This resulted in a significant difference in protein intake during the intervention of 80 ± 21 g of the protein group vs. 59 ± 11 g of the control group (P < 0.01). Change in body fat percentage showed a significant group × time interaction of decreased body fat percentage of − 1.0 ± 1.1% of the protein group vs. 0.1 ± 0.6% of the control group (P < 0.05). The group × time interaction of change in fat mass was significant (P < 0.05), and change in fat-free mass was a trend (P = 0.05). Fat-free mass of the protein group had increased with + 0.9 ± 0.6 kg (P < 0.01), and fat mass had decreased with − 0.6 ± 0.8 kg (P < 0.05), while the control group had not changed.

Conclusion

During increased daily protein intake vs. control body fat percentage decreased with unchanged physical activity during 3 months of stable body weight.     

Muscle strength and body composition as determinants of blood pressure in young men

Summary The correlations of blood pressure to various indices of muscularity and fatness were studied in 183 young healthy men (mean age 19.7, SD 2.1 years). Systolic pressure showed significant positive correlations with body fat percentage, isometric strength of trunk extensors, body mass index, lean body mass, strength of leg extensors, heart rate, and the sum of four skinfolds. Diastolic pressure had significant positive correlations with body mass index, lean body mass, body fat percentage, sum of skinfolds, strength of leg extensors, strength of trunk extensors, and age. A stepwise selective multiple regression analysis for systolic pressure resulted in four significantly correlating variables: body fat percentage (p<0.001), heart rate (p<0.01), lean body mass (p< 0.05), and strength of trunk extensors per kg body weight (p<0.05). For diastolic pressure the analysis resulted in two explaining variables: body mass index (p<0.001) and age (p<0.05). In a regression equation with 13 variables the strength of trunk flexors was negatively correlated with diastolic pressure.It is concluded that both fatness and muscularity are factors related to blood pressure in young men. The muscularity effect is more clearly associated with trunk and leg extensor strength.     

Differences in quadriceps muscle strength and fatigue between lean and obese subjects

The present study aimed to compare quadriceps femoris muscle strength and fatigue between obese (grade II and III) and nonobese adults. Ten obese (mean age: 25 years; mean BMI: 41 kg/m2) and ten lean (mean age: 27 years; mean BMI: 23 kg/m2) men were tested. Quadriceps muscle fatigue was quantified as the (percent) torque loss during a voluntary isokinetic (50 maximal contractions at 180°/s) and an electrostimulated (40 Hz) isometric protocol (5 min, 10% of the maximal torque). Maximal voluntary isometric and isokinetic torque and power were also measured. Voluntary torque loss was significantly higher (P < 0.05) in obese (−63.5%) than in lean subjects (−50.6%). Stimulated torque decreased significantly (P < 0.05) but equally in the two subject groups. Obese subjects displayed higher absolute (+20%; P < 0.01) but lower relative (i.e., normalized to body mass) (−32%; P < 0.001) muscle torque and power than their lean counterparts. Obese individuals demonstrated lower fatigue resistance during voluntary but not during stimulated knee extensions compared to their nonobese counterparts. Peripheral mechanisms of muscle fatigue—at least those associated to the present stimulated test—were not influenced by obesity. The observed quadriceps muscle function impairments (voluntary fatigue and relative strength) probably contribute to the reduced functional capacity of obese subjects during daily living activities.     

Evaluation of Margaria staircase test: the effect of body size

The purpose of this study was to evaluate the methodology of Margaria staircase test (MT) for assessment of muscle anaerobic power. Specifically, we hypothesized that due to the scaling effects the outcome of MT calculated using the standard formula that suggests the power output to be proportional to body mass [P = (m · g · h)/T; P = power output, m = body mass, g = 9.81 m/s², h = height of stairs climbed, T = running time] overestimates the effect of body size on the calculated muscle power output. Young and physically active subjects (N = 111) were tested and the relationship between P and body size (S; either body mass or height) was assessed by standard allometric model (i.e., P = a · S ^b ; where a and b were the constant multiplier and allometric parameter, respectively). The results supported the hypothesized relationship by revealing b = 0.66 (95%CI = 0.49–0.83; r = 0.59; P < 0.001) and b = 1.13 (95%CI = 0.49–0.83; r = 0.34; P < 0.001) for body mass and body height, respectively. The obtained values of b (i.e., b < 1 for body mass and b < 3 for body height) suggest that the standard formula of MT overestimates the power output of larger subjects and underestimates the power of smaller ones. Since the results were mainly in line with both the experimental findings and theoretical predictions regarding the general effects of scale on human muscle power, we propose a modified formula that provides normalized power: P _n = P/m ^0.67 = [(m · g · h)/T]/m ^0.67 = (m ^0.33 · g · h)/T. The modified formula could provide a body size independent index of muscle power that would both allow for establishing standards and enable comparison of individuals and groups of individuals of different body dimensions.     

Assessment of human knee extensor muscles stress from in vivo physiological cross-sectional area and strength measurements

Summary The physiological cross-sectional areas (CSAp) of the vastus lateralis (VL), vastus intermedius (VI), vastus medialis (VM) and rectus femoris (RF) were obtained, in vivo, from the reconstructed muscle volumes, angles of pennation and distance between tendons of six healthy male volunteers by nuclear magnetic resonance imaging (MRI). In all subjects, the isometric maximum voluntary contraction strength (MVC) was measured at the optimum angle at which peak force occurred. The MVC developed at the ankle was 746.0 (SD 141.8) N and its tendon component (F _t) given by a mechanical advantage of 0.117 (SD 0.010), was 6.367 (SD 1.113) kN. To calculate the force acting along the fibres (F _f) of each muscle, F _t was divided by the cosine of the angle of pennation and multiplied for (CSAp · CSAp^–1), where CSAp was the sum of CSAp of the four muscles. The resulting F _f values of VL, VI, VM and RF were: 1.452 (SD 0.531) kN, 1.997 (SD 0.187) kN, 1.914 (SD 0.827) kN, and 1.601 (SD 0.306) kN, respectively. The stress of each muscle was obtained by dividing these forces for the respective CSAp which was: 6.24 × 10^–3 (SD 2.54 × 10^–3) m² for VL, 8.35 × 10^–3 (SD 1.17 × 10^–3) m² for VI, 6.80 × 10^–3 (SD 2.66 × 10^–3) m² for VM and 6.62 × 10^–3 (SD 1.21 × 10^–3) m² for RE The mean value of stress of VL, VI, VM and RF was 250 (SD 19) kN m²; this value is in good agreement with data on animal muscle and those on human parallel-fibred muscle.     

湖南侗族青少年身高、体重及体表面积研究

目的了解湖南侗族青少年学生身高、体重及体表面积的发育情况。方法调查了982例(男486例,女496例)7～17岁的侗族青少年学生的身高、体重,计算出每位学生的体表面积和体重指数,并与全国青少年平均值进行比较。结果侗族青少年学生的身高、体重、体重指数及体表面积随年龄增长而增长,男生11～15岁为快速增长期,女生10～14岁为快速增长期。体重指数在14岁后出现明显的性别差异;9岁开始女生体表面积值超过男生,14岁开始男生体表面积值又超过女生,15岁以后,男女生体表面积之差逐渐加大。结论湖南侗族青少年的身高、体重及其体重指数和体表面积的发育水平均不及全国青少年的平均水平。     

Body weight as an indicator of fat-free mass in active elderly women

Objective

Fat-free mass (FFM) reduction and the tendency for a reduction in surrounding fatty issue and increase in the middle are a natural consequence of growing old and should be studied in order to gain a better understanding of the aging process. This study set out to find the FFM differences between active elderly women in two age groups (60–69 and 70–80 years) and to determine which of the anthropometric measurements, body weight (BW), abdominal circumference (AC), or body mass index (BMI) are the best predictors of FFM variation within the group.

Methods

Eighty-one (n = 81) active elderly women of the Third Age willingly signed up to participate in the research during the activities at the University of the Third Age (UTA) in Brazil. The research was approved by the Research Ethics Committee of the Faculty of Medical Sciences of the State University of Campinas (UNICAMP). Body weight (BW), height (H) and the BMI were measured according to the international standards. The AC was measured in centimetres at the H of the navel and body composition was ascertained using bioimpedance analysis. The SAS program was used to perform the statistical analysis of independent samples and parametric data.

Results

The results showed FFM values with significant differences between the two groups, with the lowest values occurring among the women who were over 70 years of age. In the analysis, the Pearson's Correlation Coefficient for each measured independent variable was ascertained, with the BW measurement showing the highest ratio (0.900).

Conclusions

The BW measurement was regarded as reliable, low-cost and easy to use for monitoring FFM in elderly women who engage in physical activities.     

The scaling of motor noise with muscle strength and motor unit number in humans

Understanding the origin of noise, or variability, in the motor system is an important step towards understanding how accurate movements are performed. Variability of joint torque during voluntary activation is affected by many factors such as the precision of the descending motor commands, the number of muscles that cross the joint, their size and the number of motor units in each. To investigate the relationship between the peripheral factors and motor noise, the maximum voluntary torque produced at a joint and the coefficient of variation of joint torque were recorded from six adult human subjects for four muscle/joint groups in the arm. It was found that the coefficient of variation of torque decreases systematically as the maximum voluntary torque increases. This decreasing coefficient of variation means that a given torque or force can be more accurately generated by a stronger muscle than a weaker muscle. Simulations demonstrated that muscles with different strengths and different numbers of motor units could account for the experimental data. In the simulations, the magnitude of the coefficient of variation of muscle force depended primarily on the number of motor units innervating the muscle, which relates positively to muscle strength. This result can be generalised to the situation where more than one muscle is available to perform a task, and a muscle activation pattern must be selected. The optimal muscle activation pattern required to generate a target torque using a group of muscles, while minimizing the consequences of signal dependent noise, is derived.     

川北医学院大学生拳头体积与身高关系研究

目的初步探索拳头体积与身高的关系。方法按照整群抽样的方法,在川北医学院男、女生宿舍楼分别随机抽取三个楼层的同学进行身高、体重和优势手拳头体积的测量与记录,用简单线性回归分析拳头体积与身高的关系。结果本研究共调查754人,身高为(164.12±8.96)cm,体重为(56.13±8.83)kg,BMI值为(20.78±2.27)kg/m2,拳头体积为(274.98±52.01)cm3。拳头体积与身高回归分析的决定系数(R2)为0.629(P<0.01)。除了肥胖对象(BMI≥28.0)外,消瘦、正常、超重对象的拳头体积与身高之间的R2均较高(0.646、0.669、0.649,P<0.01);男、女生分别分析,决定系数相对较低(0.238、0.180,P<0.01)。结论拳头体积与身高可能存在一定相关性,值得进一步研究。     

Body Composition Characteristics of a Load-Capacity Model: Age-Dependent and Sex-Specific Percentiles in 5- to 17-Year-Old Children

IntroductionBody composition assessment is superior to the use of body mass index (BMI) to characterize the nutritional status in pediatric populations. For data interpretation, suitable reference data are needed; hence, we aimed to generate age-dependent and sex-specific body composition reference data in a larger population of children and adolescents in Germany.MethodsThis is a cross-sectional study on a representative group of 15,392 5- to 17-year-old children and adolescents. Body composition was assessed by bioelectrical impedance analysis using a population-specific algorithm validated against air displacement plethysmography. Age- and sex-specific percentiles for BMI, fat mass index (FMI), fat-free mass index (FFMI), and a “load-capacity model” (characterized by the ratios of fat mass [FM]/ fatt-free mass [FFM] and FM/FFM²) were modeled using the LMS method.ResultsBMI, FMI, FFMI, FM/FFM, and FM/FFM² curves showed similar shapes between boys and girls with steady increases in BMI, FMI, and FFMI, while FM/FFM²-centiles decreased during early childhood and adolescence. Sex differences were observed in FMI and FM/FFM percentiles with increases in FMI up to age 9 years followed by a steady decrease in FM/FFM during and after puberty with a fast-growing FFMI up to age 17 in boys. The prevalence of low FFM relative to FM reached more than 60% in overweight children and adolescents.ConclusionThese pediatric body composition reference data enable physicians and public health scientists to monitor body composition during growth and development and to interpret individual data. The data point out to an early risk of sarcopenia in overweight children and adolescents.     

Plasma oestrone,oestradiol and androstenedione levels in post-menopausal women: Relation to body weight and height

To study the relation between body weight and height and the plasma sex-hormone levels we measured the plasma levels of oestrone (E₁), oestradiol (E₂) and androstenedione (A) in a group of healthy post-menopausal women with a wide range of body weight.The sex hormones were measured by radioimmunoassay with highly specific antisera after purification of the plasma extract by column chromatography.Our findings show that there is significant positive correlation between the E₁ level and body weight as well as A level and, to a lesser extent, between the E₁ level and Quetelet index. For E₂ there is no correlation with these parameters. There is also a very slight correlation between A level, body weight and Quetelet index.Calculation of the partial correlation coefficient shows that E₁ correlates to the same degree with body weight and A level, whereas the A level does not correlate with body weight at a fixed value for the E₁ level. We conclude that variation in the E₁ level depends to the same degree on the variation in body weight as well as the variation in A level.     

A cross-sectional study of the size and strength of the lower leg muscles during growth

The influences of age and sex on the cross-sectional area (CSA) and isometric strength of the ankle dorsiflexors and plantarflexors (PF) were investigated in four age groups of 121 boys and 121 girls aged: 7–9, 10–12, 13–15, and 16–18 years. A single anatomical cross-section was determined at 30% of the distance from the articular cleft between the femur and tibiacondyles by using an ultrasonic apparatus. In both sexes, the increase in age was associated with significant increases in the CSA and strength (ST) of these opposing muscle groups. The sex differences became apparent in the 13–15 year group for CSA and in the 16–18 year group for ST but the differences reduced considerably when CSA and ST were expressed per unit of the second power of the lower leg length (CSA·LL ^–2) and the product of CSA and the lower leg length (ST·CSA ^–1·LL ^–1), respectively. However,CSA·LL ^–2 of both muscles had a tendency to be increased at and over the age of 10–12 years, and was the highest at 16–18 years, andST·CSA ^–1·LL ^–1 of PF showed higher values in the older boys than in the younger. Thus, it appeared that, at least in the reciprocal muscle groups of the ankle joint, the sex differences in muscle CSA and ST during growth could be accounted for by differences in LL and muscle mass, respectively. However, other factors must also be involved to explain completely the age differences in these variables.     

Obesity and body size perceptions in a Spanish Roma population

Background: Roma people are particularly vulnerable to developing overweight and obesity. Self-perception of body image may influence the prevalence of obesity in this ethnic minority.

Aim: The objectives of this study are to estimate the prevalence of obesity, to analyse body size perceptions and preferences and to assess the relationship between body size perceptions and obesity in the Roma population.

Subjects and methods: The analyses were carried out on 372 men, women and children from the Roma population residing in the Greater Bilbao region (Basque Country, Spain). In adults, a standard figural scale was used to analyse body size perceptions and preferences in this ethnic minority.

Results: Overall 51.7% of adult and 24.4% of minor Roma individuals were obese. Both Roma men and women had inaccurate self-perceptions of their body size. Significant differences on body size perceptions were detected based on age, sex, nutritional status and socioeconomic characteristics.

Conclusion: This Roma population presents one of the highest rates of obesity worldwide. Although a certain awareness of the correct weight status was appreciated, the inability of Roma individuals to see themselves as overweight or obese may be a significant factor on the high prevalence of obesity in this population.     

Muscle strength,power and adaptations to resistance training in older people

Muscle strength and, to a greater extent, power inexorably decline with ageing. Quantitative loss of muscle mass, referred to as sarcopenia, is the most important factor underlying this phenomenon. However, qualitative changes of muscle fibres and tendons, such as selective atrophy of fast-twitch fibres and reduced tendon stiffness, and neural changes, such as lower activation of the agonist muscles and higher coactivation of the antagonist muscles, also account for the age-related decline in muscle function. The selective atrophy of fast-twitch fibres has been ascribed to the progressive loss of motoneurons in the spinal cord with initial denervation of fast-twitch fibres, which is often accompanied by reinnervation of these fibres by axonal sprouting from adjacent slow-twitch motor units (MUs). In addition, single fibres of older muscles containing myosin heavy chains of both type I and II show lower tension and shortening velocity with respect to the fibres of young muscles. Changes in central activation capacity are still controversial. At the peripheral level, the rate of decline in parameters of the surface-electromyogram power spectrum and in the action-potential conduction velocity has been shown to be lower in older muscle. Therefore, the older muscle seems to be more resistant to isometric fatigue (fatigue-paradox), which can be ascribed to the selective atrophy of fast-twitch fibres, slowing in the contractile properties and lower MU firing rates. Finally, specific training programmes can dramatically improve the muscle strength, power and functional abilities of older individuals, which will be examined in the second part of this review.     

Markers of inflammation and their association with muscle strength and mass: A systematic review and meta-analysis

BackgroundChronic inflammation has been associated with sarcopenia and its components skeletal muscle strength and muscle mass. The aim of this systematic review and meta-analysis was to determine the relationship between systemic inflammation, muscle strength and/or muscle mass in adults.MethodsAn electronic search using keywords such as ‘acute phase proteins, cytokines and sarcopenia, muscle mass, muscle strength’ was conducted via Pubmed, Web of Science and Embase from inception until the 30th of June 2020. A meta-analysis using correlation data was performed to determine the overall relationship between inflammation and muscle strength and muscle mass in adults.ResultsOverall, 168 articles; 149 cross-sectional articles (n = 76,899 participants, 47.0 % male) and 19 longitudinal articles (n = 12,295 participants, 31.9 % male) met inclusion criteria. Independent of disease state, higher levels of C reactive protein (CRP), Interleukin (IL)-6 and Tumor necrosis factor (TNF)α were associated with lower handgrip and knee extension strength (CRP; r = −0.10, p < 0.001, IL-6; r = −0.13, p < 0.001, TNFα; r = −0.08, p < 0.001 and CRP; r = −0.18, p < 0.001, IL-6; r = −0.11, p < 0.001, TNFα; r = −0.13, p < 0.001 respectively) and muscle mass (CRP; r = −0.12, p < 0.001, IL-6; r = −0.09, p < 0.001, TNFα; r = −0.15, p < 0.001). Furthermore, higher levels of systemic inflammatory markers appeared to be associated with lower muscle strength and muscle mass over time.ConclusionHigher levels of circulating inflammatory markers are significantly associated with lower skeletal muscle strength and muscle mass.     

Scaling of muscle power to body size: the effect of stretch-shortening cycle

The present study investigates the relationship between muscle power recorded in vertical jumps and body size, and explores possible differences in this relationship between the concentric (CON) and stretch-shortening cycle (SSC) muscle action. Physical education students (N = 159) were tested with the performance of various CON and SSC maximum vertical jumps. The relationship between muscle power (P) and body size (S) was assessed by P=aS^b where a and b were the constant multiplayer and scaling exponent, respectively. With respect to body mass and fat-free mass, the scaling exponents b for mean muscle power (calculated from the ground reaction force) in CON and SSC jumps were within the range 0.69–0.82 and 0.90–1.15, respectively. With respect to body height, the scaling exponent was higher (0.76–0.97 and 1.23–1.79, respectively), but the observed relationship proved to be relatively weak. However, when jump height was used as an index of muscle power, the same exponents were close to zero (suggesting no relationship with any of the indices of body size) in all the jumps except an SSC based hopping jump that demonstrated a weak but positive relation to body size. In conclusion, muscle power could scale to body size at a higher rate than predicted by geometric similarity (i.e. b = 0.67), while larger individuals could gain more when switching from CON to SSC muscle action. These findings could be based on a non-geometric scaling of transversal with respect to longitudinal dimensions and/or on different scaling rates of muscles and tendons.     

A longitudinal study of changes in body composition and basal metabolism in physically active elderly men

Ageing in the elderly is usually characterised by loss of fat-free mass (FFM) and reduction in basal metabolic rate (BMR). These age-related changes probably vary in rate, timing and extent between subjects in response to differences in leisure or occupational physical activity, disease and several other factors. Information on rates of change in BMR and FFM is limited by study design (most published work is cross-sectional rather than longitudinal), and possibly by methodology (use of imprecise and/or biased methods for assessment of changes in body composition). In the present study BMR and body composition were first measured in 22 physically active elderly men (mean age 62) in good health and measurements were repeated 6.5 years later. Changes in BMR, FFM and percentage body fat were small and not statistically significant over the time period (pairedt,P > 0.05). The study suggests that physically active elderly men in good health in this age range can show very small age-related declines in BMR and FFM.     

Effect of whole body vibration exercise on muscle strength and proprioception in females with knee osteoarthritis

The purpose of this study was to assess the effect of whole body vibration (WBV) exercise on muscle strength and proprioception in female patients with osteoarthritis in the knee (knee-OA). A single blinded, randomised, controlled trial was performed in an outpatient clinic on 52 female patients diagnosed with knee-OA (mean age 60.4 years ± 9.6). They were randomly assigned to one of 3 groups: 1. WBV-exercise on a stable platform (VibM; n = 17 (mean age, 61.5 ± 9.2)), WBV-exercise on a balance board (VibF; n = 18 (mean age, 58.7 ± 11.0)), or control group (Con; n = 18 (mean age, 61.1 ± 8.5)).The WBV groups trained twice a week for 8 weeks, with a progressively increasing intensity. The WBV groups performed unloaded static WBV exercise.The following were measured: knee muscle strength (extension/flexion) and proprioception (threshold for detection of passive movement (TDPM)). Self-reported disease status was measured using WOMAC.It was found that muscle strength increased significantly (p < 0.001) in VibM compared to Con. Isometric knee-extension significantly increased (p = 0.021) in VibM compared to Con. TDPM was significantly improved (p = 0.033) in VibF compared to Con, while there was a tendency (p = 0.051) for VibM to perform better compared to Con. There were no effects in the self-reported disease status measures.This study showed that the WBV-exercise regime on a stable platform (VibM) yielded increased muscle strength, while the WBV-exercise on a balance board (VibF) showed improved TDPM. The WBV-exercise is a time-saving and safe method for rehabilitation of women with knee-OA.