Nutrient Intake, Performance, and Body Composition of Preseason Wrestlers

College athletes, especially in weight class sports, often experience energy deficits. Athletes competing in weight class sports such as wrestling are at greatest risk for deficiencies and little is known about the relationships between body composition, nutrient intake, and performance in these athletes. The purposes of this study were to (1) quantify macronutrient and micronutrient intake of pre-season male collegiate wrestlers and compare to estimated needs, and (2) examine relationships among nutritional intakes, body composition, and performance measurements of strength and anaerobic capacity. Male Division I wrestlers (n = 11, age: 21.3 ± 1.7 years, wrestling experience: 14.9 ± 2.5 years) were recruited during pre-season. Nutrient intake was collected from a 3-day food diary. A 7-site skinfold assessment determined fat-free mass (FFM) to estimate total daily energy expenditure (eTEE). Isokinetic and isometric strength were evaluated by a Biodex dynamometer. Anaerobic capacity was tested on a stationary cycle ergometer. Eight of eleven wrestlers were energy deficient based on estimated needs. Mean intake of four micronutrients fell below the Recommended Dietary Allowances (RDA). Significant correlations were found between dietary intake, strength and anaerobic performance variables (r = 0.603 - 0.902, p = 0.0001 - 0.05). However, after accounting for FFM, these relationships were no longer significant. Nutrient intake in tandem with body composition affects performance for weight class athletes. Achieving high FFM during the preseason may be advantageous for wrestling performance. Nutrient intake and body composition should be monitored so coaches and health professionals can create individualized recommendations to help athletes optimize performance.

Sex Differences in Test-Retest Reliability of Near-Infrared Spectroscopy During Postocclusive Reactive Hyperemia of the Vastus Lateralis

ABSTRACT

Shoemaker, ME, Smith, CM, Gillen, ZM, and Cramer, JT. Sex differences in test-retest reliability of near-infrared spectroscopy during postocclusive reactive hyperemia of the vastus lateralis. J Strength Cond Res 38(2): e40-e48, 2024-The purpose of this study was to determine test-retest reliability for vascular reactivity measures and ranges for normalization of near-infrared spectroscopy (NIRS) variables from the vastus lateralis using postocclusive reactive hyperemia (PORH) procedure in male subjects, female subjects, and combined. Concentrations of oxygenated hemoglobin (Hb) + myoglobin (Mb) (O 2 Hb) and deoxygenated Hb + Mb (HHb) to derive total Hb + Mb (THb), difference in Hb + Mb signal (Hbdiff), and muscle tissue oxygen saturation (StO 2 ) from the vastus lateralis were measured during the PORH in 12 male subjects (age: 23.17 ± 1.77 years; stature: 180.88 ± 4.59 cm; and mass: 81.47 ± 9.68 kg) and 10 female subjects (age: 23.80 ± 2.07 years; stature: 165.95 ± 4.92 cm; and mass: 70.93 ± 10.55 kg) on 2 separate days. Adipose tissue thickness at the NIRS site was measured with ultrasonography. There were no significant differences between the mean values from visit 1 to visit 2 ( p > 0.076-0.985). In the composite sample, intraclass correlation coefficient (ICC) and coefficient of variation (CV) ranged from 0.35 to 0.91 and 4.74 to 39.18%, respectively. In male subjects, ICC and CV values ranged from 0.57 to 0.89 and 2.44 to 28.55%, respectively. In female subjects, ICC and CV values ranged from -0.05 to 0.75 and 7.83 to 61.19%, respectively. Although NIRS variables were overall reliable during PORH, when separated by sex, reliability in male subjects generally increased, whereas female subjects were not reliable, suggesting adipose tissue thickness may be a contributing factor. Understanding sex differences in reliability is important when using this technique for normalization or examining vascular reactivity during athletic performance. With greater utilization of NIRS monitoring in athletes to examine training adaptations, it is important for practitioners to understand the capabilities and potential limitations of the tool.

Metabolic Flexibility and Inflexibility: Pathology Underlying Metabolism Dysfunction

Metabolic flexibility can be defined as the ability of the skeletal muscle to adjust its utilization of substrate pathways [...].

Contributions from incumbent police officer's physical activity and body composition to occupational assessment performance

Introduction

Police officers must perform various tasks in unpredictable work environments and potentially volatile situations. This study aimed to determine if cardiovascular fitness, body composition, and physical activity levels could predict performance in a Midwest Police Department's Physical Readiness Assessment (PRA).

Methods

Researchers collected data from thirty incumbent police officers (33.9 ± 8.3 years, female = 5). Anthropometric data included height, body mass, body fat percentage (BF%), fat-free mass (FFM), and maximal hand grip strength. The police officers also completed a physical activity rating (PA-R) scale to estimate maximal oxygen consumption (V ˙ O2max) and the International Physical Activity Questionnaire (IPAQ). Police officers then conducted their department's PRA. Stepwise linear regression analyses were used to determine the relationship between predictor variables and PRA performance. Pearson's product-moment correlations investigated relationships between anthropometric, physical fitness, and physical activity variables and PRA performance using SPSS (v.28). The significance level was set at p < 0.05.

Results

Descriptive data for the sample includes BF%: 27.85 ± 7.57%, FFM: 65.73 ± 10.72 kg, hand grip strength: 55.51 ± 11.07 kg, weekday sedentary time (WST): 328 ± 28.26 min, weekend day sedentary time (WDST): 310 ± 28.92 min, daily moderate-to-vigorous physical activity (MVPA): 29.02 ± 39.41 min, PRA: 273.6 ± 51.4 s and estimated V ˙ O2max: 43.26 ± 6.35 mL kg-1 min-1. The stepwise regression analyses indicated that BF% was predictive of PRA time (R2 = 0.32, p < 0.01); estimated V ˙ O2max predictive of PRA time (R2 = 0.45, p < 0.001). There were significant correlations between BF % and PRA time (r = 0.57, p < 0.001), PA-R and MVPA (r = 0.71, p < 0.001), %BF % and WDST (r = -0.606, p < 0.001), hand grip and FFM (r = 0.602, p < 0.001) and PA-R and PRA time (r = -0.36, p < 0.05).

Discussion

The results of this exploratory study highlight that higher estimated V ˙ O2max and lower BF% were the best predictors for faster PRA completion times, accounting for 45% and 32% of the variance, respectively. The findings of this study support the need for wellness and fitness initiatives in law enforcement agencies focused on increasing cardiovascular fitness and physical activity while decreasing BF% to ensure optimal performance in policing and overall health.

Immunomodulatory Effects of Vitamin D and Prevention of Respiratory Tract Infections and COVID-19

Little is known about potential protective factors for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), referred to as COVID-19. Suboptimal vitamin D status is a risk factor for immune dysfunction, respiratory tract infections (RTIs), and viral infections. Supplementation of vitamin D (2000-4000 IU) has decreased incidence and complications from RTIs, respiratory distress syndrome, and pneumonia and may be beneficial in high-risk populations. Given the possible link between low vitamin D status and RTIs, such as COVID-19, this review examined whether vitamin D supplementation can be supported as a nutritional strategy for reducing risk of infection, complications, and mortality from COVID-19 and found that the relationship between vitamin D and RTIs warrants further exploration.

Differences in muscle energy metabolism and metabolic flexibility between sarcopenic and nonsarcopenic older adults

BACKGROUND

Metabolic flexibility is the ability of skeletal muscle to adapt fuel utilization to the demand for fuel sources [carbohydrates (CHO) and fats (FAT)]. The purpose of this study was to explore muscle energy metabolism and metabolic flexibility under various conditions in sarcopenic (S) versus nonsarcopenic (NS) older adults.

METHODS

Twenty-two older adults aged 65 years or older were categorized as NS [n = 11; mean ± standard deviation (SD); age = 73.5 ± 6.0 years (males, n = 5; females, n = 6)] or S [n = 11; 81.2 ± 10.5 years (males, n = 6; females, n = 5) based on handgrip strength, body composition and physical performance. Indirect calorimetry was recorded before and after consumption of a high-CHO meal and during aerobic and anaerobic exercise. Respiratory quotient (RQ), CHO and FAT oxidation were assessed. Venous blood samples were collected for glucose and insulin concentrations.

RESULTS

At rest, compared with NS, S exhibited a 5-8% higher RQ at 0 (0.72 vs. 0.76) and 120 (0.77 vs. 0.82), 150 (0.76 vs. 0.80), and 180 min (0.74 vs. 0.80) (P = 0.002-0.025); 59-195% higher CHO oxidation at 0, 120, and 180 min (0.0004-0.002 vs. 0.001-0.002 g·min^-1 ·kg^-1) (P = 0.010-0.047); and 20-31% lower FAT oxidation at 0, 15, and 90-180 min (0.0009-0.0022 vs. 0.0011-0.002 g·min^-1 ·kg^-1 ) (P = 0.004-0.038). Glucose levels were significantly elevated in S versus NS at 0, 60 and 75 min (144.64-202.78 vs. 107.70-134.20 mg·dL^-1 ) but not insulin. During aerobic exercise, RQ was 5% greater (0.90 vs. 0.86) (P = 0.039), and FAT oxidation was 35% lower at 6-8 min (0.003 vs. 0.005 g·min^-1 ·kg^-1 ) (P = 0.033) in S versus NS. During anaerobic exercise, CHO oxidation was 31% greater in NS versus S at 60-80% time to exhaustion (0.011 vs. 0.007 g·min^-1 ·kg^-1 ) (P = 0.015). Per cent contribution to energy expenditure was greater in S for CHO but lower for FAT at 0 (CHO: 22% vs. 10%; FAT: 78% vs. 91%) and 120-180 min (CHO: 35-42% vs. 17-25%; FAT: 58-65% vs. 75%-84%) (P = 0.003-0.046) at rest and 6-8 min during aerobic exercise (CHO: 70% vs. 57%; FAT: 30% vs. 45%) (P = 0.046).

CONCLUSIONS

The data show differences in skeletal muscle energy metabolism and substrate utilization between S and NS at rest, transitioning from fasted to fed state, and during exercise. Compared with NS, S displayed a diminished ability to adapt fuel utilization in response to feeding and exercise, reflecting metabolic inflexibility. Impaired metabolic flexibility could be a mechanism underlying the losses of strength and physical function accompanying sarcopenia.

Comparing the torque- and power-velocity relationships between children and adolescents during isokinetic leg extension muscle actions

The purpose of this study was to use polynomial regression analyses to examine the torque- and power-velocity relationships and calculate and compare the vertices of these nonlinear models, and how they relate to measurements of muscle size and maximal strength, between male and female children and adolescents during maximal isokinetic leg extension muscle actions. Sixteen children (n = 8 males, n = 8 females) and 22 adolescents (n = 11 males, n = 11 females) participated in this study. Measurements of growth included age, maturity offset, height, body mass, fat-free mass, and quadriceps femoris muscle cross-sectional area (CSA). Participants completed maximal voluntary isometric contractions (MVICs) of the leg extensors and maximal voluntary isokinetic leg extensions at 60, 120, 180, 240, and 300°·s^-1. Variables calculated during all leg extension muscle actions included peak torque (PT, Nm) and mean power (MP, W). Polynomial regression analyses determined the model of best fit for the PT- and MP-velocity relationships. For each participant, the vertex from the PT- and MP-velocity quadratic models were quantified as the predicted maximum velocity of last measurable torque (V_PT) and the predicted velocity of maximum mean power (V_MP), respectively. Measurements of growth, PT and MP at all velocities, V_PT, and V_MP were greater in the adolescents than children. When normalized to CSA, V_PT and V_MP remained greater for adolescents than children, and exhibited low to very high relationships with measurements of growth. When normalized to MVIC strength, V_PT and V_MP were no longer different between children and adolescents and exhibited negligible to low relationships with measurements of growth. The results of the present study suggest that the ability to produce torque and power at high velocities may be more dependent on muscle strength than muscle size, which suggests that mechanisms other than muscular hypertrophy affect torque and power production at high velocities in young males and females.

Test-Retest Reliability of Static and Countermovement Power Push-Up Tests in Young Male Athletes

Bohannon, NA, Gillen, ZM, Shoemaker, ME, McKay, BD, Gibson, SM, Cramer, JT. Test-Retest Reliability of Static and Counter-Movement Power Push-Up Tests in Young Male Athletes. J Strength Cond Res 34(9): 2456-2464, 2020-The primary purpose of this study was to evaluate test-retest reliability of the static (SP) and countermovement (CMP) power push-up test in young male athletes. The secondary purpose was to compare the reliability of vertical ground reaction forces versus torque measurements during the power push-up tests. Twenty boys (age = 11.60 ± 1.15 years) performed SPs and CMPs on force plates with the knees as the fulcrum on 2 laboratory visits separated by 2-7 days. Performance measurements included peak force (PF), peak rate of force development (pRFD), peak torque (PT), peak rate of torque development (pRTD), peak power (PP), average power (AP), eccentric impulse (ECC), and concentric impulse (CON) for both power push-up techniques. Age, maturity offset, height, body mass, fat-free mass, and estimated arm cross sectional area were obtained as measurements of growth. Intraclass correlation coefficients (ICC), SEM, coefficients of variation, and minimum detectable changes (MDC) were reported. Only PF (ICC = 0.87-0.88, SEM = 59-84 N) and PT (ICC = 0.89-0.90, SEM = 60-88 N·m) showed acceptable reliability. Neither pRFD, pRTD, PP, AP, ECC, or CON were reliable outcomes. There were no meaningful differences between force-time and torque-time curve measurements. The SP showed slightly lower CVs (33-34%) than the CMP (CVs = 39-40%). Coaches and practitioners would need to see 58-71% increases in upper-body strength measurements evaluated via power push-up on force plates to be 95% confident that the improvements exceeded the measurement variability.

Endogenous versus exogenous carbohydrate oxidation measured by stable isotopes in pre-pubescent children plus 13C abundances in foods consumed three days prior

PURPOSE

The purposes of the present study were to (a) examine resting metabolism, substrate utilization, and endogenous versus exogenous carbohydrate (CHO) oxidation before and after 30-g rapidly-digesting carbohydrate (RDC) ingestion using indirect calorimetry and breath test analysis of stable isotope concentrations in pre-pubescent children and (b) report the 13C abundances in foods consumed for three days prior.

METHODS

Nineteen children (n = 10 boys, n = 9 girls) at Tanner stage I or II participated (mean age ± 95% CI = 9.84 ± 0.77 y) in this study. Food was administered to the children for three days preceding their scheduled breath tests. Breath tests and indirect calorimetry were performed after an 8-h fast before and 60 min following consumption of a 30-g simple RDC drink consisting of maltodextrin and sucrose. Open circuit spirometry and indirect calorimetry monitored resting metabolism and CHO oxidation. Separate breath samples were taken every 15 min. Samples of all foods and breath samples were analyzed for 13C and 12C abundances with a stable-isotope mass spectrometer.

RESULTS

13C in expired breath samples were -23.81 ± 1.64‰ at baseline and increased every 15 min after consumption of the CHO drink (p < 0.001-0.009). Cumulative total, endogenous, and exogenous CHO utilization increased during the post-prandial period (p < 0.001). Endogenous CHO oxidation was consistently greater than exogenous CHO oxidation (p < 0.001-0.002).Blood glucose was elevated from baseline at 30- and 60-min post-prandial (p < 0.001). Insulin did not change over time (p = 0.184).

CONCLUSIONS

The foods provided during the 3-day controlled diet effectively minimized 13C variation prior to metabolic testing. The 13C abundances of foods reported herein should serve as practical recommendations to reduce 13C intake before breath tests. While endogenous CHO oxidation remained greater in proportion to exogenous CHO oxidation, these findings suggest that even a relatively small amount of RDC can increase exogenous CHO oxidation and blood glucose in normal-weight children. To further examine shifts in endogenous versus exogenous CHO utilization, we recommend that future studies take steps to minimize 13C variation before breath tests and examine changes in substrate metabolism at rest and during exercise in normal weight and overweight pre-pubescent children.

CLINICAL TRIAL REGISTRATION NUMBER

NCT03185884.

Peak Torque Explains More Unique Variability in Growth Measurements than Rate of Torque Development in Young Boys and Girls

Gillen, ZM, Shoemaker, ME, McKay, BD, Bohannon, NA, Gibson, SM, and Cramer, JT. Peak torque explains more unique variability in growth measurements than rate of torque development in young boys and girls. J Strength Cond Res 34(9): 2507-2514, 2020-This study reported test-retest reliability and evaluated collinearity for isometric leg extension and flexion peak torque (PT) and rate of torque development (RTD) in young boys and girls. Measurements of growth included height, body mass, fat-free mass, maturity offset, and leg extensor and flexor muscle cross-sectional area. Maximal isometric contractions quantified PT and RTD. Intraclass correlation coefficients (ICCs), SEM, coefficients of variation, and minimum detectable changes quantified test-retest reliability. Zero-order correlations and first-order partial correlations evaluated collinearity. Peak torque from leg extension and flexion exhibited ICCs ≥ 0.90, RTD from leg extension and flexion exhibited ICCs ≥ 0.38. Partialing out leg flexion PT reduced the relationships between leg extension PT and growth (rPText, growth.PTflex = 0.392-0.605). Partialing out leg extension PT eliminated the relationships between leg flexion PT and growth (rPTflex, growth.PText = 0.098-0.263). Partialing out leg extension RTD reduced the relationships between PT and growth (rPText, growth.RTDext = 0.516-0.775). Partialing out leg extension PT eliminated the relationships between RTD and growth (|rRTDext, growth.PText| = 0.001-0.148). Leg extension PT was more reliable and explained the most unique variability in growth among young boys and girls. In contrast, RTD was less reliable and was fully accounted for by PT, indicating that RTD may be an unnecessary measurement in studies of young boys and girls.

Influences of the Stretch-Shortening Cycle and Arm Swing on Vertical Jump Performance in Children and Adolescents

Gillen, ZM, Shoemaker, ME, McKay, BD, Bohannon, NA, Gibson, SM, and Cramer, JT. Influences of the stretch-shortening cycle and arm swing on vertical jump performance in children and adolescents. J Strength Cond Res XX(X): 000-000, 2020-This study compared the influences of the stretch-shortening cycle and arm swing on vertical jump performance during static jumps (SJs), counter-movement jumps (CMJs), and CMJs with arm swing (CMJAs) in young male and female athletes. Twenty-one boys (age = 12.1 ± 1.1 years) and 21 girls (age = 12.1 ± 1.1 years) performed SJs, CMJs, and CMJAs on force plates that sampled at 1 kHz. Measurements included peak force, rate of force development, peak power (PP), eccentric impulse (ECC), concentric impulse (CON), estimated jump height (JH), and changes in PP and JH across vertical jumps. Measurements of growth included age, maturity offset, height, body mass, fat-free mass, and thigh muscle cross-sectional area. Analyses of variance were used to analyze growth measurements across sex, as well as vertical jump outcome measures. Pearson product moment correlation coefficients were used to determine the relationships between changes in PP and JH across vertical jumps and growth measurements. There were differences in PP and JH such that SJ < CMJ < CMJA (p < 0.001), and ECC such that SJ < CMJA < CMJ (p ≤ 0.048). Changes in PP were greater from the SJ to CMJ than CMJ to CMJA (p ≤ 0.001). The change in PP from the SJ to CMJ exhibited moderate-to-high relationships with growth measurements for boys and girls (r = 0.543-0.803). Because young children may not have the skeletal musculature or strength necessary to absorb and reapply large eccentric preloading forces, future studies should consider using the CMJA, rather than the CMJ, to maximize vertical jump performance and minimize ECC. Coaches and practitioners can expect approximately 27-33% greater PP and 15-17% greater estimated JH when an arm swing is included during the CMJ.

Sex-specific relationships among iron status biomarkers, athletic performance, maturity, and dietary intakes in pre-adolescent and adolescent athletes

Background

The purpose of this study was to examine relationships among biomarkers of iron status, athletic performance, growth and development, and dietary intakes in pre-adolescent and adolescent male and female athletes.

Methods

Two-hundred and forty-nine male (n = 179) (mean ± standard deviation for age = 12.0 ± 2.1 years, height = 156.3 ± 13.9 cm, and weight = 49.1 ± 16.5 kg) and female (n = 70) (12.0 ± 2.2 years, 152.4 ± 12.3 cm, 45.3 ± 14.5 kg) athletes volunteered for capillary blood sample, anthropometric, athletic performance, and dietary intake assessments. Outcomes included maturity offset from peak height velocity, percent body fat, estimated muscle cross-sectional areas, vertical jump height (VJ), broad jump distance (BJ), pro-agility time (PA), L-cone time, 20-yard dash time (20YD), power push up (PPU) force, dietary intakes, and ferritin, soluble transferrin receptor (sTfR), and hemoglobin (Hb) concentrations.

Results

Athletic performance was consistently correlated with Hb in males (r = .237–.375, p < 0.001–0.05) and with sTfR (r = .521–.649, p < 0.001–0.004) and iron intake (r = .397–.568, p = 0.001–0.027) in females. There were no relationships between dietary intakes and ferritin, sTfR, or Hb (p > 0.05). After partialing out age and height, VJ, PA, LC, and 20YD remained correlated with Hb in males (|r_Hb,y.Age| = .208–.322, p = 0.001–0.041; |r_Hb,y.Height| = .211–.321, p = 0.001–0.038). After partialing out iron intake, PA and LC remained correlated with sTfR in females (|r_{sTfR,y.ironintake}| = .516–.569, p = 0.014–0.028).

Conclusions

Iron status biomarkers demonstrated sex-specific relationships with anaerobic exercise performance in youth athletes, which may be more dependent on maturity status and dietary intake than age. Moderate relationships between sTfR and athletic performance in adolescent female athletes emphasizes the importance of iron intake in this demographic.

High Prevalence of Poor Iron Status Among 8- to 16-Year-Old Youth Athletes: Interactions Among Biomarkers of Iron, Dietary Intakes, and Biological Maturity

Objective: The purpose of this study was to determine the prevalence of poor iron status in young athletes throughout the stages of iron deficiency and assess sex differences with iron deficiency in relation to growth and development and dietary intake.Methods: A cross-sectional analysis evaluated young male and female athletes (n = 91) between the ages 8 and 16 years. Anthropometric assessments, body composition, dietary intakes, and blood samples measuring ferritin, soluble transferrin receptor (sTfR), and hemoglobin (Hb) were examined. Prevalence was calculated as percentages, and independent samples t tests examined sex differences. Pearson product-moment correlation coefficient analyses quantified relationships among variables for the composite sample and each sex separately.Results: Iron depletion (low ferritin) was present in 65% and 86%, low iron levels (sTfR) in 51% and 68%, and anemia (low Hb) in 46% and 53% of the males and females, respectively. As iron deficiency progressed from low ferritin to high sTfR to anemia, prevalence decreased in both sexes, but always remained higher in females. Males were greater than females for weight, arm muscle size, and ferritin concentrations, while females were greater than males for biological maturity (p ≤ 0.05). Dietary iron intake was moderately to highly correlated (r = 0.543-0.723, p ≤ 0.05) with growth and development in females, but not males.Conclusions: Prevalence of poor iron status was higher than expected, particularly in adolescent females. Since rapid growth combined with sports participation may create high demands for iron bioavailability, emphasis may need to be placed on dietary iron intake for young athletes, particularly females.

Performance Differences between National Football League and High School American Football Combine Participants

PURPOSE

The purpose of this study was to determine magnitudes of differences for anthropometric and athletic performance scores between high school and elite college-level American football players.

METHOD

Participants included high school-age (n = 3,666) athletes who participated in American football combines, as well as elite college-level (n = 5,537) athletes who participated in the National Football League (NFL) scouting combine. Combine data included position; height; weight; 10-, 20-, and 40-yard dash; pro-agility (PA); L-cone drill (LC); vertical jump (VJ); and broad jump (BJ). Athletes were separated into their respective position group, defensive back (DB), wide receiver (WR), linebacker (LB), quarterback (QB), running back (RB), tight end (TE), defensive line (DL), and offensive line (OL) for analysis of performance differences. Percent differences for each dependent variable were calculated to quantify magnitudes of differences.

RESULTS

NFL combine participants scored 3% to 25% better on all measurements, with the largest differences between weight and VJ (14%-25%).

CONCLUSION

The largest measurement-specific differences between high school-age and elite college-level American football players were body size and power. Although it may seem intuitive that elite college-level players would perform better, these data provide a unique perspective to high school players, parents, and coaches, giving new information to use when designing measurement-specific athletic development programs. Thus, strength and conditioning professionals may benefit from emphasizing increases in muscle mass and power output in strength and conditioning programs.

Muscle strength, size, and neuromuscular function before and during adolescence

PURPOSE

To compare measurements of muscle strength, size, and neuromuscular function among pre-adolescent and adolescent boys and girls with distinctly different strength capabilities.

METHODS

Fifteen boys (mean age ± confidence interval: 13.0 ± 1.0 years) and 13 girls (12.9 ± 1.1 years) were categorized as low strength (LS, n = 14) or high strength (HS, n = 14) based on isometric maximal voluntary contraction strength of the leg extensors. Height (HT), seated height, and weight (WT) determined maturity offset, while percent body fat and fat-free mass (FFM) were estimated from skinfold measurements. Quadriceps femoris muscle cross-sectional area (CSA) was assessed from ultrasound images. Isometric ramp contractions of the leg extensors were performed while surface electromyographic amplitude (EMG_RMS) and mechanomyographic amplitude (MMG_RMS) were recorded for the vastus lateralis (VL). Neuromuscular efficiency from the EMG and MMG signals (NME_EMG and NME_MMG, respectively) and log-transformed EMG and MMG vs. torque relationships were also used to examine neuromuscular responses.

RESULTS

HS was 99-117% stronger, 2.3-2.8  years older, 14.0-15.7 cm taller, 20.9-22.3 kg heavier, 2.3-2.4 years more biologically mature, and exhibited 39-43% greater CSA than LS (p ≤ 0.001). HS exhibited 74-81% higher NME_EMG than LS (p ≤ 0.022), while HS girls exhibited the highest NME_MMG (p ≤ 0.045). Even after scaling for HT, WT, CSA, and FFM, strength was still 36-90% greater for HS than LS (p ≤ 0.031). The MMG_RMS patterns in the LS group displayed more type I motor unit characteristics.

CONCLUSIONS

Neuromuscular adaptations likely influence strength increases from pre-adolescence to adolescence, particularly when examining large, force-producing muscles and large strength differences explained by biological maturity, rather than simply age.

Uvulitis and Hemophilus influenzae b bacteremia

Uvulitis and Hemophilus influenzae b (HIb) bacteremia occurred in two infants. Uvulitis may be associated with HIb bacteremia, with or without epiglottitis. An acutely inflamed uvula in a febrile infant should alert the physician to the possibility of HIb bacteremia and potentially serious sequelae. Hospitalization and parenteral antibiotic therapy are recommended.