Rapid Muscle Activation Changes Across a Competitive Collegiate Female Soccer Season

Objective: The purpose of this study was to examine the effects of a competitive soccer season on rapid activation properties of the knee extensors and flexors in Division II female soccer players. Methods: Eighteen collegiate female soccer players participated in the present study, however, due to injuries during the season a final sample of 16 players were included for study analysis. Participants performed two maximal voluntary isometric contractions (MVICs) of the knee extensors and flexors before, during, and at the end of a competitive college soccer season. Electromyography root mean square (EMG RMS; μV), rate of EMG rise (RER; %Peak EMG•s-1), and electromechanical delay (EMD; ms) were examined on both legs for the knee extensors and flexors. Results: EMG RMS at early time intervals (0-50, 0-100, and 50-100 ms) and RER at 0-75 ms for the knee extensors and flexors significantly increased from the pre-season to the end of the season (P ≤ 0.010-0.026, η2=0.36-0.81). EMD of the knee flexors significantly decreased at the mid-season and the end of the season compared to the pre-season (P \u3c 0.001, η2=0.95). Conclusions: These findings may have important implications for monitoring improvements on thigh neuromuscular activation and developing lower extremity injury prevention strategies during a competitive collegiate female soccer season

The relationship between muscular strength and work performance in blue-collar workers

Objective: The present study examined the influence of workplace manual labor on measures of muscular fitness, with a secondary aim to investigate the relationship between muscular fitness and work performance in blue-collar (BC) workers. Methods: Leg extension isokinetic strength at slow and fast velocities, hamstring and hip-flexor flexibility, and low back muscular endurance were examined in young and older BC workers and white-collar (WC) controls, while work performance was examined in the BC cohort. Results: There were no differences in muscular fitness variables between BC and WC groups; however, the older men had lower low back muscular endurance (−43.0%) and strength at slow (−9.4%) and fast (−12.7%) velocities. Work performance was associated with strength at fast velocities (r = 0.633) in the older BC workers. Conclusions: Leg strength may influence work performance, with higher velocities becoming more important in older workers

Effects of age and muscle action type on acute strength and power recovery following fatigue of the leg flexors

Short-term strength and power recovery patterns following fatigue have received little research attention, particularly as they pertain to age-specific responses, and the leg flexors (i.e., hamstrings) muscle group. Thus, research is warranted addressing these issues because both age-related alterations in the neuromuscular system and mode of muscle action (e.g., eccentric, concentric, isometric) may differentially influence recovery responses from fatigue. The aim of this study was to investigate the strength and power recovery responses for eccentric, concentric, and isometric muscle actions of the leg flexors in young and older men following an isometric, intermittent fatigue-inducing protocol. Nineteen young (age = 25 ± 3 years) and nineteen older (71 ± 4) men performed maximal voluntary contractions (MVCs) for eccentric, concentric, and isometric muscle actions followed by a fatigue protocol of intermittent (0.6 duty cycle) isometric contractions of the leg flexors at 60 % of isometric MVC. MVCs of each muscle action were performed at 0, 7, 15, and 30 min following fatigue. Peak torque (PT) and mean power values were calculated from the MVCs and the eccentric/concentric ratio (ECR) was derived. For PT and mean power, young men showed incomplete recovery at all time phases, whereas the older men had recovered by 7 min. Eccentric and isometric muscle actions showed incomplete recovery at all time phases, but concentric recovered by 7 min, independent of age. The ECR was depressed for up to 30 min following fatigue. More rapid and pronounced recovery in older men and concentric contractions may be related to physiological differences specific to aging and muscle action motor unit patterns. Individuals and clinicians may use these time course responses as a guide for recovery following activity-induced fatigue

Development and examination of a functional reactive agility test for older adults

Background Reactive agility tests have become popular in sport for talent identification; however, the ability of these tests to evaluate physical function and falls risk in clinical populations warrants future study. Aim To examine the reliability and construct validity of a novel functional reactive agility test (FRAT) across the lifespan. Methods Forty-three young (24 ± 2 years), 32 middle-aged (50 ± 2 years), and 19 old (66 ± 4 years) men performed a FRAT that included a rapid lateral movement (1.5 m) in response to a randomly delayed visual stimulus. Test–retest reliability and minimum difference (MD) scores were determined from a subset of participants. Results There was no systematic error (P \u3e 0.087) between testing days, and the intraclass correlation coefficients, standard error of measurement (% of the mean), and MD values for decision time, movement time, and total time ranged from 0.876 to 0.949, 4.16–9.24%, and 0.128–0.138 s, respectively. The young men had faster decision times (P = 0.027) when compared to the older men and faster total times when compared to the middle-aged and older men (P \u3c 0.001). Discussion The FRAT demonstrated acceptable reliability and construct validity between different age groups. Conclusion Due to its limited space requirements, the FRAT may serve as a useful tool in future studies examining clinical populations

Age related differences in maximal and rapid torque characteristics of the leg extensors and flexors in young, middle-aged and old men

The decline in maximal and rapid isometric torque characteristics may compromise functional living abilities in aging adults while loco-motor muscle groups, such as the leg extensors and flexors, may exhibit different torque–time age related decreases. The purpose of the present study was to examine the age-related differences in maximal and rapid torque characteristics of the leg extensor and flexor muscle groups in young, middle-aged, and old men. Sixty-five healthy men were categorized by age as young (n = 25; mean ± SD age = 24.9 ± 3.0 years), middle-aged (n = 22; age = 50.6 ± 4.0 years), and old (n = 18; age = 66.8 ± 4.5 years). Participants performed maximal voluntary contractions (MVCs) of the leg extensors and flexors and an estimated thigh cross sectional area (eThighCSA) assessment. Peak torque (PT), peak rate of torque development (RTDpeak), absolute RTD and the contractile impulse (IMPULSE) were calculated at time intervals of 30, 50, 100 and 200 ms from the torque–time curve. Relative RTD was calculated at 10, 20, 30, 40 and 50% of MVC from the normalized torque–time curves. PT, RTDpeak and later rapid torque variables (RTD100, RTD200, and IMPULSE200) were greater (P ≤ 0.05) in the young and middle-aged when compared to the old men for both muscle groups. Early (RTD30,50; IMPULSE30,50) and late (IMPULSE100) rapid torque variables were greater (P ≤ 0.05) for the young and middle-aged than the old men for the leg extensors but not the leg flexors, except for RTD30, in which there was no difference between young and old. There were no differences for all relative RTD variables between age groups (P \u3e 0.05). eThighCSA was lower in the old compared to the young (P = 0.001) and middle-aged (P = 0.016) men. Maximal and rapid torque characteristics were preserved in middle-aged men but greatly reduced in older men with differential effects at early and late portions of the torque–time curve between the leg extensors and flexors. Significant decreases in absolute maximal and rapid torque production with no change in relative RTD across age groups and lower eThighCSA in old men may suggest that the loss of rapid torque producing capacities observed in older men may be largely a function of mechanisms associated with loss of muscle strength and muscle mass

The influence of age on the viscoelastic stretch response

Passive stretching is commonly recommended to help reduce passive stiffness in older adults, yet their acute viscoelastic stretch responses are still unclear. The purpose of this study was to determine the influence of age on the acute viscoelastic responses to a practical stretching intervention. Twenty-two younger (24 ± 3 years) and 14 older (67 ± 3 years) males performed four 30-second passive stretches of the plantar flexors at a predetermined torque threshold. The absolute and relative change in stress relaxation (decline in torque during each 30-second stretch) and creep (increase in ankle joint angle across the 4 stretches) were recorded. Passive stiffness was calculated as the slope of the angle-torque curve at 10° angle of dorsiflexion. There were no differences for the absolute stress relaxation responses (p ≥ 0.118); however, the relative change in stress relaxation was greater (p = 0.010) for the younger vs. older men at stretch 1 (13.0 vs. 8.6%) and decreased across stretches for the younger men (stretch 1 \u3e 3 and 4; p ≤ 0.018), whereas the older men demonstrated a similar relative change across all 4 stretches (p = 0.917). No age related differences were found for either the absolute or relative creep responses (p ≥ 0.072). Passive stiffness was also greater in the older men (p = 0.044). These results suggest that the younger men displayed a greater initial relative stress relaxation response that diminished across the repeated stretches, whereas the older men experienced a smaller relative response that remained constant across the four 30-second stretches. However, the increase in range of motion for a given stretch torque (creep) across all 4 stretches was similar between groups despite differences in passive stiffness

Occupational differences for nutrient intake and physical-activity levels in young and middle-aged men

BACKGROUND: Physical demands may vary between white collar and blue collar occupations when evaluating specific physiological differences such as one’s weight, body mass index and body fat percentage. OBJECTIVE: To explore nutritional, anthropometric, and physical-activity differences between young and middle-aged WC and BC workers. METHODS: Ninety-one male participants aged 19–64 that were either WC and/or BC workers completed a 3-day food recall, modified Baecke Questionnaire, and had their height, weight, body mass index and body fat percentage measured. Participants were classified as: young-white-collar, young-blue-collar, middle-white-collar or middle-blue-collar workers. RESULTS: No nutritional differences within ages or between occupations were reported. Body mass index and body fat percentage were lower for young vs. middle-aged workers. Lastly, physical-activity at work was higher for young and middle-aged Blue collar workers, while White collar workers participated in more physical activity outside of work. CONCLUSIONS: The present findings suggest that the observed increases in body fat percentage and body mass index with age, are independent of occupation

Effects of maximal versus submaximal intensity fatigue-protocols on maximal torque responses of the leg extensors

Recent studieshaverevealed that neuromuscularfatigue leads toincreased electromechanical delay (EMD), and that differential recoverypatternsare exhibited betweenthe leg extensorand flexormuscle groups, whichmay adversely affectperformance and possibly increaselower extremity injury risks. However,it is unknownwhetherthese effects are influenced by theintensity levelofthefatigueprotocol. PURPOSE: Thepurposeofthis study was to investigate theeffectsofafatigue-inducing bout ofsubmaximal,andmaximal intermittent isometric contractions on the electromechanicaldelay ofthe legextensorsand flexors incollege-aged females.METHODS: Twenty young (age=21.23±1.41years) recreationally activefemalesparticipatedinafamiliarizationtrial followed byfour experimental fatigue sessions,separated byseven(±1) days. All sessionsbegan with participants performing maximal voluntary contractions(MVCs)followed by arandomly assigned fatigue-inducing protocol consisting of intermittent isometric contractions ofthe leg extensorsorflexorsusing a 0.6 duty cycle (6s contraction,4s relaxation)ateither 50% or 100%ofMVCuntil volitionalfatigue. MVCs were again performedat 0,7, 15,and 30 min post fatigue. RESULTS:Athree-wayrepeatedmeasures ANOVA (muscle[legextensorsvs.leg flexors]× intensity [submaximal vs.maximal]× time[Pre-vs.Post0vs.Post7vs.Post15vs.Post30]) wasusedto analyze the EMD data. There was nosignificant three-way interaction (P=0.134), nora two-way interaction formuscle × time (P=0.778),intensity × time (P=.072), ormuscle × intensity(P=0.842). However,there was a maineffect fortime (P=0.0001) where theEMD ofthe legextensorsand flexorswas greateratall postfatigue time periods comparedto Pre-,and Post0 was greatercomparedtoall other post time periods(P=0.001). Additionally,the EMD ofthe leg flexorswas greater(P=0.011) comparedtothe legextensors.CONCLUSIONS:Thesefindings showsimilar fatigue-inducedEMDeffectsand recoverypatternsbetweenthe legextensorsand flexorsat both maximal and submaximal intensities. ThesustainedincreasedEMD of the extensors and flexors during recovery may have important injury and performance implications inavarietyof populationsand settings; and theseeffects may be similarly incurred at bothsubmaximal and maximal contractionintensitie