Effects of acute and 2‐week administration of oral salbutamol on exercise performance and muscle strength in athletes

Our objective was to investigate effects of acute and 2‐week administration of oral salbutamol on repeated sprint ability, exercise performance, and muscle strength in elite endurance athletes. Twenty male elite athletes [VO_2max: 69.4 ± 1.8 (Mean ± SE) mL/min/kg], aged 25.9 ± 1.4 years, were included in a randomized, double‐blinded and placebo‐controlled parallel study. At baseline, after acute administration, and again after 2‐week administration of the study drugs (8 mg salbutamol or placebo), subjects' maximal voluntary contraction (MVC) of m. quadriceps and isometric endurance of m. deltoideus were measured, followed by three repeated Wingate tests. Exercise performance at 110% of VO_2max was determined on a bike ergometer. Acute administration of salbutamol increased peak power during first Wingate test by 4.1 ± 1.7% (P < 0.05). Two‐week administration of salbutamol increased (P < 0.05) peak power during first and second Wingate test by 6.4 ± 2.0 and 4.2 ± 1.0%. Neither acute nor 2‐week administration of salbutamol had any effect on MVC, exercise performance at 110% of VO_2max or on isometric endurance. No differences were observed in the placebo group. In conclusion, salbutamol benefits athletes' sprint ability. Thus, the present study supports the restriction of oral salbutamol in competitive sports.     

Urinary incontinence and other pelvic floor dysfunctions in female athletes in Brazil: A cross‐sectional study

The pelvic floor (PF) provides support to all pelvic organs, as well as appropriately closure/opening mechanism of the urethra, vagina, and anus. Therefore, it is likely that female athletes involved in high‐impact and in strong‐effort activities are at risk for the occurrence of urinary incontinence (UI). This study aimed to investigate the occurrence of UI and other PF dysfunctions (PFD) [anal incontinence (AI), symptoms of constipation, dyspareunia, vaginal laxity, and pelvic organ prolapse] in 67 amateur athletes (AT) compared with a group 96 of nonathletes (NAT). An ad hoc survey based on questions from reliable and valid instruments was developed to investigate the occurrence of PFD symptoms. The risk of UI was higher in AT group (odds ratio: 2.90; 95% CI: 1.50–5.61), mostly among artistic gymnastics and trampoline, followed by swimming and judo athletes. Whereas, AT group reported less straining to evacuate (OR: 0.46; 95% CI: 0.22–0.96), manual assistance to defecate (OR: 0.24; 95% CI: 0.05–1.12), and a higher stool frequency (OR: 0.29; 95% CI: 0.13–0.64) than NAT group. The occurrence of loss of gas and sexual symptoms was high for both groups when compared with literature, although with no statistical difference between them. Pelvic organ prolapse was only reported by nonathletes. Athletes are at higher risk to develop UI, loss of gas, and sexual dysfunctions, either practicing high‐impact or strong‐effort activities. Thus, pelvic floor must be considered as an entity and addressed as well. Also, women involved in long‐term high‐impact and strengthening sports should be advised of the impact of such activities on pelvic floor function and offered preventive PFD strategies as well.     

Evidence of imbalanced adaptation between muscle and tendon in adolescent athletes

Adolescence may be regarded as a critical phase of tissue plasticity in young growing athletes, as the adaptation process of muscle‐tendon unit is affected by both environmental mechanical stimuli and maturation. The present study investigated potential imbalances of knee extensor muscle strength and patellar tendon properties in adolescent compared with middle‐aged athletes featuring long‐term musculotendinous adaptations. Nineteen adolescent elite volleyball athletes [(A), 15.9 ± 0.6 years] and 18 middle‐aged competitively active former elite volleyball athletes [(MA), 46.9 ± 0.6 years] participated in magnetic resonance imaging and ultrasound‐dynamometry sessions to determine quadriceps femoris muscle strength, vastus lateralis morphology and patellar tendon mechanical and morphological properties. There was no significant age effect on the physiological cross‐sectional area of the vastus lateralis and maximum knee extension moment (P > 0.05) during voluntary isometric contractions. However, the patellar tendon cross‐sectional area was significantly smaller (A: 107.4 ± 27.5 mm²; MA: 121.7 ± 39.8 mm²) and the tendon stress during the maximal contractions was significantly higher in adolescent compared with the middle‐aged athletes (A: 50.0 ± 10.1 MPa; MA: 40.0 ± 9.5 MPa). These findings provide evidence of an imbalanced development of muscle strength and tendon mechanical and morphological properties in adolescent athletes, which may have implications for the risk of tendon overuse injuries.     

The isokinetic rotator cuff strength ratios in overhead athletes: Assessment and exercise effect

ObjectiveMuscle strength imbalance in the shoulder region can be considered as a predisposing factor in the development of movement dysfunctions, possibly leading to overuse injuries. Repetitive overhead throwing, performed in sports, may result in muscle imbalance between the external (ER) and internal (IR) rotators. Muscle strength measured with an isokinetic device, is reported as a concentric (CON) or eccentric (ECC) force. The balance between an agonist and an antagonist is mentioned as a ratio (CON/CON or ECC/CON). The aim of this systematic literature review is to provide an overview of the existing evidence considering the isokinetic muscle strength ratios of ER and IR of the shoulder in healthy overhead athletes. In addition, the effect of exercise programs on these ratios was investigated.MethodsTwo online databases (Web of Science and PubMed) were consulted using different search strategies. Articles were selected based on inclusion and exclusion criteria. All included articles were assessed on their methodological quality.Results and conclusionsThere is moderate evidence for a lower functional deceleration ratio (ECC ER/CON IR) at the dominant side. This lower ratio is due to a large overweight of CON IR strength on that side. There is no consensus about which exercise program is the most effective in altering the shoulder isokinetic strength ratios.     

Reference values of hip abductor torque among youth athletes: Influence of age,sex and sports

Objective(1) To determine the reference values of hip abductor torque in youth athletes; (2) To investigate the influence of sex, age and sports on hip abductors torque.DesignCross-sectional.SettingSports clubs.Subjects301 volleyball, basketball and futsal athletes between 10 and 19 years of age.Main outcome measuresMean value of three maximal isometric hip abductor torques, evaluated using a hand-held dynamometer.ResultsThe mean values of maximal isometric hip abductor torque ranged from 1.03 to 1.50 Nm/kg. The dominant hip abductor torque values were greater in 15–19 years old (1.41 ± 0.27 Nm/kg) than in 10–14 years old (1.12 ± 0.31 Nm/kg). In addition, the hip abductor torque values were smaller in basketball players (1.15 ± 0.31 Nm/kg) than futsal (1.34 ± 0.37 Nm/kg) and volleyball players (1.28 ± 0.25 Nm/kg). The comparison of hip abductor torque between futsal and volleyball players revealed no difference. The hip abductor torque values were greater in male volleyball athletes (1.28 ± 0.25 Nm/kg) than female volleyball athletes (1.13 ± 0.22 Nm/kg).ConclusionThis study established reference values for maximal isometric hip abductor torque in youth volleyball, basketball and futsal athletes. In addition, the results demonstrated that sex, age and sports influenced hip abductor torque.     

Measurements from image‐based three dimensional pelvic floor reconstruction: A study of inter‐ and intraobserver reliability

Purpose

To describe inter‐ and intraobserver reliability of 3D measurements of female pelvic floor structures.

Materials and Methods

Twenty reconstructed MR datasets of primiparas at 6–12 months postpartum were analyzed. Pelvic organ measurements were independently made twice by three radiologists blinded to dataset order. A “within‐reader” analysis, a “between‐reader” analysis, and the intraclass correlation (ICC), and standard deviation ratio (SDR) were computed for each parameter. Fifteen continuous variables and one categorical variable were measured.

Results

Eight continuous parameters showed excellent agreement (ICC >0.85 / SDR <0.40), five parameters showed relatively good agreement (ICC >0.70 / SDR ≥0.40, <0.60). Two parameters showed poor agreement (ICC ≤0.70 and/or SDR ≥0.60). The categorical variable showed poor agreement.

Conclusion

Agreement was best where landmark edges were well defined, acceptable where more “reader judgment” was needed, and poor where levator defects made landmarks difficult to identify. Automated measurement algorithms are under study and may improve agreement in the future. J. Magn. Reson. Imaging 2009;30:344–350. © 2009 Wiley‐Liss, Inc.     

Jump-land characteristics and muscle strength development in young athletes: a gender comparison of 1140 athletes 9 to 17 years of age

BACKGROUND: Many authors have speculated that altered neuromuscular control and strength of the lower extremity are responsible for the gender disparity in knee ligament injury rates. HYPOTHESIS: Significant increases in normalized quadriceps and hamstrings strength and limb symmetry on single-legged hop test occur with age. No gender differences in strength occur until age 14 years, after which boys generate greater peak torques than do girls. Age and gender do not influence lower limb alignment on a drop-jump test. STUDY DESIGN: Cross-sectional study; Level of evidence, 3. METHODS: We studied the effects of age and gender in 1140 athletes, 9 to 17 years old, on muscle strength and neuromuscular control during functional activities. Isokinetic quadriceps and hamstrings strength was measured at 300 deg/s. Limb symmetry was assessed with single-legged hop tests. A video drop-jump test determined lower limb alignment in the coronal plane. RESULTS: Extension peak torques significantly increased with age; maximum strength was noted in girls at age 13 years and in boys at age 14 years (P < .001). Although maximum flexion strength occurred in boys at age 14 years (P < .001), girls had only slight increases from ages 9 to 11 years (P = not significant). Boys aged 14 to 17 years had significantly greater normalized isokinetic strength than did age-matched girls. No age or gender effects existed in limb alignment on the drop-jump test or limb symmetry on single-legged hop testing. CONCLUSION: Maximum hamstrings strength was noted in female athletes by age 11 years, compared with age 14 years in male athletes, and a distinct lower limb valgus alignment existed in the majority of all athletes on landing. The absence of a gender difference in lower limb alignment on landing suggests other factors may be responsible for the gender disparity in knee ligament injury rates.     

Kinematic,strength, and stiffness adaptations after a short‐term sled towing training in athletes

One of the most frequently used methods for training the sprint‐specific strength is the sled towing. To date, no studies have been conducted to explore the effects of this method after a training period in well‐trained athletes. The purpose of this study was to determine the effects of 4 weeks of resisted sprint training with sled towing. Twenty‐two trained athletes experienced in the use of weighted sled (WS) participated in the study. They conducted the same 3‐week training to level their initial condition. After that they were distributed in two groups, unresisted (UR) and WS training. They carried out the same 4‐week, 2 days/week sprint‐specific training, only differing in that the experimental group performed sprints with a (WS) which caused a reduction of 7.5% of their maximum velocity. Pre‐ and posttest were conducted which included the measurement of sprint kinematics, muscular strength (including isoinertial, isokinetic, and jump measurements), and sprinting stiffness (leg and vertical). Results show different adaptations in the groups although no interaction effect was found. The WS group improved the velocity in the transition phase, while the UR group improved the velocity in the maximum velocity phase. No improvements in the height of the jump tests were found.     

The association between lower extremity strength ratios and the history of injury in collegiate athletes

ContextStrength ratios are important because imbalances in opposing muscle groups can cause articular instability and subsequently increase the risk of musculoskeletal injury (MSKI). Therefore, the purpose of this study was to evaluate the association between lower extremity (LE) musculoskeletal isometric strength ratios and the history of LE MSKI.ParticipantsOne hundred eighty-two NCAA Division 1 soccer, football, volleyball, and basketball athletes.InterventionsAll isometric strength assessments were measured bilaterally using a handheld dynamometer. Strength assessments included: ankle inversion/eversion, ankle dorsiflexion/plantarflexion, knee flexion/extension, hip abduction/adduction, and hip external/internal rotation. LE MSKI history was collected through self-report; a report of the LE MSKI sustained in the one year prior to testing were collected.ResultsThe hip external/internal rotation ratio was statistically significant for side to side differences in the non-injured (NINJ) group (p = 0.001). The dominant leg of the NINJ group had a mean external/internal rotation ratio of 1.109 ± 0.221, and the non-dominant leg had a mean ratio of 1.177 ± 0.208.ConclusionsThere were no statistically significant differences between the injured (INJ) and NINJ groups. This could indicate that injury history does not play a role in current strength ratios and could suggest that the athletes in the INJ group are performing successful rehabilitation for their injuries.     

Quadriceps strength changes across the continuum of care in adolescent male and female athletes with anterior cruciate ligament injury and reconstruction

ObjectivesTo examine the quadriceps strength (QUADS) on the surgical (SURG) and non-surgical (Non-SURG) limbs in adolescent male and female athletes at pre-operative (PRE), 12 weeks post-operative (12WK), and return to sport (RTS) time points following ACL injury and reconstruction.DesignProspective cohort study design.SettingClinical Research Laboratory.Participants66 adolescent athletes.Main outcome measuresIsokinetic QUADS of the SURG and Non-SURG limbs at the PRE, 12WK, and RTS time points were assessed and compared between each time point.ResultsBoth male and female participants had significantly lower 12 WK QUADS in the SURG limb than the PRE QUADS, but the RTS QUADS was significantly greater than the 12WK QUAD (p < 0.05). However, only female participants had greater RTS QUADS as compared to the PRE QUADS (p < 0.001). For the Non-SURG limb, only male participants had a significant improvement over time (PRE vs RTS; p < 0.001).ConclusionAdolescent males and females differ in their QUADS recovery across the continuum of care following ACLR. Clinicians should consider this pattern of recovery when treating adolescent males and females.     

Effects of contract‐relax vs static stretching on stretch‐induced strength loss and length–tension relationship

The purpose of this study was to determine the acute effects of contract‐relax stretching (CRS) vs static stretching (SS) on strength loss and the length‐tension relationship. We hypothesized that there would be a greater muscle length‐specific effect of CRS vs SS. Isometric hamstring strength was measured in 20 healthy people at four knee joint angles (90°, 70°, 50°, 30°) before and after stretching. One leg received SS, the contralateral received CRS. Both stretching techniques resulted in significant strength loss, which was most apparent at short muscle lengths [SS: P = 0.025; stretching × angle P < 0.001; 11.7% at 90° P < 0.01; 5.6% at 70° nonsignificant (ns); 1.3% at 50° ns; ?3.7% at 30° ns. CRS: P < 0.001; stretching × angle P < 0.001; 17.7% at 90°, 13.4% at 70°, 11.4% at 50°, all P < 0.01, 4.3% at 30° ns]. The overall stretch‐induced strength loss was greater (P = 0.015) after CRS (11.7%) vs SS (3.7%). The muscle length effect on strength loss was not different between CRS and SS (stretching × angle × stretching technique P = 0.43). Contrary to the hypothesis, CRS did not result in a greater shift in the length–tension relationship, and in fact, resulted in greater overall strength loss compared with SS. These results support the use of SS for stretching the hamstrings.     

Effects of high‐intensity interval cycling performed after resistance training on muscle strength and hypertrophy

Aim of the study was to investigate whether high‐intensity interval cycling performed immediately after resistance training would inhibit muscle strength increase and hypertrophy expected from resistance training per se. Twenty‐two young men were assigned into either resistance training (RE; N = 11) or resistance training plus high‐intensity interval cycling (REC; N = 11). Lower body muscle strength and rate of force development (RFD), quadriceps cross‐sectional area (CSA) and vastus lateralis muscle architecture, muscle fiber type composition and capillarization, and estimated aerobic capacity were evaluated before and after 8 weeks of training (2 times per week). Muscle strength and quadriceps CSA were significantly and similarly increased after both interventions. Fiber CSA increased significantly and similarly after both RE (type I: 13.6 ± 3.7%, type IIA: 17.6 ± 4.4%, type IIX: 23.2 ± 5.7%, P < 0.05) and REC (type I: 10.0 ± 2.7%, type IIA: 14.8 ± 4.3% type IIX: 20.8 ± 6.0%, P < 0.05). In contrast, RFD decreased and fascicle angle increased (P < 0.05) only after REC. Capillary density and estimated aerobic capacity increased (P < 0.05) only after REC. These results suggest that high‐intensity interval cycling performed after heavy‐resistance exercise may not inhibit resistance exercise‐induced muscle strength/hypertrophy after 2 months of training, while it prompts aerobic capacity and muscle capillarization. The addition of high‐intensity cycling after heavy‐resistance exercise may decrease RFD partly due to muscle architectural changes.     

Heritability estimates of muscle strength‐related phenotypes: A systematic review and meta‐analysis

The purpose of this study was to clarify the heritability estimates of human muscle strength‐related phenotypes (H²‐msp). A systematic literature search was conducted using PubMed (through August 22, 2016). Studies reporting the H²‐msp for healthy subjects in a sedentary state were included. Random‐effects models were used to calculate the weighted mean heritability estimates. Moreover, subgroup analyses were performed based on phenotypic categories (eg, grip strength, isotonic strength, jumping ability). Sensitivity analyses were also conducted to investigate potential sources of heterogeneity of H²‐msp, which included age and sex. Twenty‐four articles including 58 measurements were included in the meta‐analysis. The weighted mean H²‐msp for all 58 measurements was 0.52 (95% confidence intervals [CI]: 0.48–0.56), with high heterogeneity (I²=91.0%, P<.001). Subgroup analysis showed that the heritability of isometric grip strength, other isometric strength, isotonic strength, isokinetic strength, jumping ability, and other power measurements was 0.56 (95% CI: 0.46–0.67), 0.49 (0.47–0.52), 0.49 (0.32–0.67), 0.49 (0.37–0.61), 0.55 (0.45–0.65), and 0.51 (0.31–0.70), respectively. The H²‐msp decreased with age (P<.05). In conclusion, our results indicate that the influence of genetic and environmental factors on muscle strength‐related phenotypes is comparable. Moreover, the role of environmental factors increased with age. These findings may contribute toward an understanding of muscle strength‐related phenotypes.     

Effects of resistance training with moderate vs heavy loads on muscle mass and strength in the elderly: A meta‐analysis

The purpose of the present study was to perform a meta‐analysis to compare the efficacy of heavy (～80% of one repetition maximum, 1RM) vs light‐moderate load (～45% 1RM) resistance training (RT) programs in inducing strength gains and skeletal muscle hypertrophy in elderly people. To assess the role of training volumes, studies in which training protocols were matched for mechanical work were independently analyzed. In all 15 studies included (448 subjects, age 67.8 years), when comparing heavy with light‐moderate loads, strength gains tended to be larger following RT with higher intensities of load, with the resulting total population effect being μ = 0.430 (P = 0.060). Effect sizes were substantially smaller in “work‐matched” studies (μ = 0.297, P = 0.003). Training with higher loads also provoked marginally larger gains in muscle size, although the degree of training‐induced muscle hypertrophy was generally small (0.056 < μ < 0.136). To conclude, provided a sufficient number of repetitions is performed, RT at lower than traditionally recommended intensities of load may suffice to induce substantial gains in muscle strength in elderly cohorts.     

Knee isokinetic muscle strength and balance ratio in female soccer players of different age groups: a cross-sectional study

ABSTRACT

Background: As a consequence of years of soccer training and sexual maturation, there is an increase in lower body muscle mass and strength especially in the knee extensors and flexors muscles. In this context, the lack of knee joint stability, resulting from strength imbalance between knee extensor and flexors muscles, has been associated with knee injuries. The aim of this study was to compare the knee flexor and extensor muscle peak torque, average power, contralateral deficit, conventional and functional balance ratios of female soccer players from different age groups.

Methods: Sixty-six female soccer players were divided into four groups: under 13 (U13), under 15 (U15), under 17 (U17) years old and professional (PRO). Flexor and extensor knee muscle strength in concentric and eccentric actions of both limbs were assessed using isokinetic dynamometer.

Results: For the dominant limb, the knee concentric extensor muscles peak torques, assessed at 60 and at 240 deg/sec, and the average power of U15 group were significantly higher than U13 group. Extensor muscle average power of the PRO group was higher than U17. Dominant knee flexor average power of U15 was significantly higher than the U13 group. Peak torque at 60 deg/sec and 240 deg/sec and average power of the PRO group were higher than the U17 group. No differences were found regarding the eccentric action for flexor and extensor muscles. Conventional and functional balance ratios were similar among all age group, except for U13, which presented higher values than the U15 group for the dominant limb.

Conclusions: The greatest improvement in muscular performance occur when the athlete starts practicing soccer (after U13) and when they become professional (after U17) and the balance ratios, and muscle balance ratios remain stable in all age groups, although they are below the recommended level in the literature, which may increase the risk for lower limb injury.     

Effects of hamstring‐emphasized neuromuscular training on strength and sprinting mechanics in football players

The objective of this study was to examine the effects of a neuromuscular training program combining eccentric hamstring muscle strength, plyometrics, and free/resisted sprinting exercises on knee extensor/flexor muscle strength, sprinting performance, and horizontal mechanical properties of sprint running in football (soccer) players. Sixty footballers were randomly assigned to an experimental group (EG) or a control group (CG). Twenty‐seven players completed the EG and 24 players the CG. Both groups performed regular football training while the EG performed also a neuromuscular training during a 7‐week period. The EG showed a small increases in concentric quadriceps strength (ES = 0.38/0.58), a moderate to large increase in concentric (ES = 0.70/0.74) and eccentric (ES = 0.66/0.87) hamstring strength, and a small improvement in 5‐m sprint performance (ES = 0.32). By contrast, the CG presented lower magnitude changes in quadriceps (ES = 0.04/0.29) and hamstring (ES = 0.27/0.34) concentric muscle strength and no changes in hamstring eccentric muscle strength (ES = ?0.02/0.11). Thus, in contrast to the CG (ES = ?0.27/0.14), the EG showed an almost certain increase in the hamstring/quadriceps strength functional ratio (ES = 0.32/0.75). Moreover, the CG showed small magnitude impairments in sprinting performance (ES = ?0.35/?0.11). Horizontal mechanical properties of sprint running remained typically unchanged in both groups. These results indicate that a neuromuscular training program can induce positive hamstring strength and maintain sprinting performance, which might help in preventing hamstring strains in football players.     

Higher psycho‐physiological refinement in world‐class Norwegian athletes: brain measures of performance capacity

This study tested the hypothesis that the degree of psycho‐physiological development is related to performance level in world‐class athletes. We compared physiological and psychological patterns of 33 Norwegian world‐class athletes to patterns in 33 average performing athletes. The subjects were matched for gender, age, and type of sport. Electroencephalography activity was recorded to measure brain integration; skin conductance was recorded to measure habituation to a loud stimulus; and paper‐and‐pencil tests were given to assess self‐development, moral development, and frequency of peak experiences. A factor analysis (varimax rotation) reduced the eight variables to three factors that together accounted for 65.3% of the total variance: (1) physiological integration – brain integration and habituation rates, (2) self‐ and moral development, and (3) peak experiences. A MANOVA conducted on the factor scores showed a significant main effect for the experimental group collapsing across the three factors (P<0.0001). Individual ANOVAs showed significantly higher values for development (P=0.021) and physiological integration (P<0.0001) factor scores for the world‐class athletes. The above measures can be seen as different expressions of an underlying dimension – human development. These data support the concept that higher psycho‐physiological growth underlies higher performance.     

Analysis of sex‐specific injury patterns and risk factors in young high‐level athletes

This study analyzed sex‐specific injury patterns and risk factors in young athletes (n=256) from 12 sport disciplines practicing at the national or the international level in the Grand‐Duchy of Luxembourg. Injury occurrence as a result of sport practice was analyzed retrospectively over the year 2006 using a standardized self‐administered questionnaire. Overall incidence was not different between girls and boys (1.20 and 1.21 injuries/1000 athlete‐hours, respectively), but in the context of team sport competition girls tended to be at a greater risk (rate ratio 2.05, P=0.053). Girls had a higher proportion of injuries in the ankle/foot region compared with boys (34.8% vs 16.8%). No sex‐related differences were found regarding injury severity. Multivariate logistic regression (controlling for age and practice volume) revealed that girls' team sports were associated with a greater injury risk compared with individual sports [odds ratio (OR) of 4.76], while in boys this was observed for racket sports (OR=3.31). Furthermore, physical or emotional stress tended to be a specific risk factor in girls. There was a tendency for injury outside sports to be coupled to a higher injury risk in girls and boys. Consideration of sex‐specific injury patterns and risk factors could be of importance for effective injury prevention.