Influence of muscle strength, power, and rapid force capacity on maximal club head speed in male national level golfers.

This study investigated the relationships between maximal club head speed (CHS) and physiological and anthropometric parameters in 21 national-level male golfers (age: 21.9 ± 3.9 years; handicap: +1.1 ± 1.7). Maximal isometric strength (MVC) was measured during isometric mid-thigh pull and bench press, while MVC and rate of force development (RFD) were measured during isometric leg press. Power, lower limb stiffness, positive impulse, jump height and RFDdyn were measured during countermovement jump (CMJ). Moreover, rotational trunk power, active range of motion (AROM) and anthropometrics were determined. Comparisons were made between participants with high (FTG) and low (STG) CHS, respectively. FTG demonstrated greater isometric mid-thigh pull and isometric bench press MVC, leg press RFD, rotational trunk power, and CMJ parameters (except RFDdyn) as well as reduced hip AROM compared to STG (P < 0.01). CHS was positively correlated to isometric mid-thigh pull and isometric bench press MVC, leg press RFD, rotational trunk power and CMJ parameters (P < 0.01). In conclusion, strong positive correlations were observed between maximal CHS and maximal strength and power parameters. Consequently, improving maximal neuromuscular strength and power may be considered of importance for golfers, as greater CHS and accompanying driving distance may lead to competitive advantages.

First-time anterior cruciate ligament injury in adolescent female elite athletes: a prospective cohort study to identify modifiable risk factors.

PURPOSE: To identify modifiable biomechanical and neuromuscular anterior cruciate ligament (ACL) injury risk factors for first-time ACL injury in adolescent female elite football and team handball players. METHODS: Adolescent female elite football and handball players with no previous ACL injury participated in the present study. At baseline, players were tested during side-cutting manoeuvres performed in a 3-dimensional motion analysis laboratory with concomitant electromyography (EMG) measurements. Maximal isometric lower limb muscle strength was assessed by handheld dynamometry. Players were prospectively followed for 2 years after baseline testing, and all magnetic resonance imaging (MRI) verified ACL injuries were registered. The effect of 16 risk factor candidates on the relative risk (RR) of ACL injury was estimated using Poisson regression analysis. RESULTS: Ninety players (age 16.9 ± 1.2 years) were included in the analyses. Nine first-time ACL injuries (injury incidence 10.0% (95% confidence interval (CI) 5.4-18.6%)) were registered during the 2-year follow-up period. Four risk factor candidates were significantly associated with the risk of ACL injury: (1) hip flexion angle at initial contact (IC) [RR 0.56, 95% confidence interval (CI) 0.34-0.92], (2) internal knee rotation angle at IC [RR 1.13, 95% CI 1.08-1.19], (3) semitendinosus EMG activity 50 ms prior to IC [RR: 0.62, 95% CI 0.43-0.89], and (4) external hip rotator strength [RR: 0.77, 95% CI 0.66-0.89]. CONCLUSION: Four distinct ACL injury risk factors related to the side-cutting manoeuvre were identified in a population of adolescent female elite football and team handball players with no previous ACL injury. As ACL injury typically occur during side-cutting, intervention programmes to modify these risk factors pose a promising strategy for ACL injury prevention in adolescent female elite football and team handball. LEVEL OF EVIDENCE: II.

Blood-flow restricted resistance training in patients with sporadic inclusion body myositis: a randomized controlled trial.

OBJECTIVES: To investigate the effect of 12 weeks of low-load blood-flow restricted resistance (BFR) training on self-reported and objective physical function, and maximal muscle strength in patients with sporadic inclusion body myositis (sIBM). METHOD: Twenty-two patients with sIBM were randomized into a training group (BFR group) or a non-exercising control group, according to CONsolidated Standards Of Reporting Trials (CONSORT) guidelines. The BFR group performed 12 weeks of BFR training twice per week. The primary outcome was the physical function domain of the 36-item Short Form Health Survey (pf-SF-36), which was used to measure self-reported physical function. All patients performed physical function tests (2-Minute Walk Test, Timed Up and Go, and 30-Second Chair Stand), completed the Inclusion Body Myositis Functional Rating Scale (IBMFRS), and were tested for isolated knee extensor muscle strength. RESULTS: No effects of the training intervention were observed for pf-SF-36 or the objective physical function tests. Leg muscle strength decreased in controls (-9.2%, p = 0.02), but was unaltered in the BFR group (+0.9%, p = 0.87), resulting in a between-group difference in the per-protocol analysis (p = 0.026). Between-group differences in baseline to follow-up changes emerged for IBMFRS, in favour of the BFR group (p = 0.018). CONCLUSION: Twelve weeks of BFR training did not improve self-reported or objective physical function in these sIBM patients. However, the training protocol had a preventive (retaining) effect on the disease-related decline in leg muscle strength, which may aid the long-term preservation of physical function and postpone the need for healthcare assistance.

Community perspective on the INSIGHT Strategic Timing of AntiRetroviral Treatment (START) trial.

Determining when to start antiretroviral treatment (ART) is vitally important for people living with HIV. Yet the optimal point at which to start to maximize clinical benefit remains unknown. In the absence of randomized studies, current guidelines rely on conflicting observational data and expert opinion, and consequently diverge on this point. In the USA, ART is recommended irrespective of CD4 cell count. The World Health Organization now recommends starting ART at a CD4 cell count of 500 cells/µL, while the threshold for the UK and South Africa remains at 350 cells/µL. The Strategic Timing of AntiRetroviral Treatment (START) study, one of the largest clinical trials on the treatment of HIV infection, will answer this question. START compares two treatment strategies: immediate treatment at a CD4 cell count of 500 cells/µL or higher versus deferring treatment until the CD4 cell count decreases to 350 cells/µL or until AIDS develops. START includes seven substudies, five of which will clarify the relative contributions of HIV and ART in common comorbidities. START is fully enrolled and expected to be completed in 2016. HIV advocates support the study's design and have been involved from inception to enrolment. The trial will produce rigorous data on the benefits and risks of earlier treatment. It will inform policy and treatment advocacy globally, benefitting the health of HIV-positive people.

Lower limb asymmetry in mechanical muscle function: A comparison between ski racers with and without ACL reconstruction.

Due to a high incidence of anterior cruciate ligament (ACL) re-injury in alpine ski racers, this study aims to assess functional asymmetry in the countermovement jump (CMJ), squat jump (SJ), and leg muscle mass in elite ski racers with and without anterior cruciate ligament reconstruction (ACL-R). Elite alpine skiers with ACL-R (n = 9; 26.2 ± 11.8 months post-op) and uninjured skiers (n = 9) participated in neuromuscular screening. Vertical ground reaction force during the CMJ and SJ was assessed using dual force plate methodology to obtain phase-specific bilateral asymmetry indices (AIs) for kinetic impulse (CMJ and SJ phase-specific kinetic impulse AI). Dual x-ray absorptiometry scanning was used to assess asymmetry in lower body muscle mass. Compared with controls, ACL-R skiers had increased AI in muscle mass (P < 0.001), kinetic impulse AI in the CMJ concentric phase (P < 0.05), and the final phase of the SJ (P < 0.05). Positive associations were observed between muscle mass and AI in the CMJ concentric phase (r = 0.57, P < 0.01) as well as in the late SJ phase (r = 0.66, P < 0.01). Future research is required to assess the role of the CMJ and SJ phase-specific kinetic impulse AI as a part of a multifaceted approach for improving outcome following ACL-R in elite ski racers.

Alterations in molecular muscle mass regulators after 8 days immobilizing Special Forces mission.

In military operations, declined physical capacity can endanger the life of soldiers. During special support and reconnaissance (SSR) missions, Special Forces soldiers sustain 1-2 weeks full-body horizontal immobilization, which impairs muscle strength and performance. Adequate muscle mass and strength are necessary in combat or evacuation situations, which prompt for improved understanding of muscle mass modulation during SSR missions. To explore the molecular regulation of myofiber size during a simulated SSR operation, nine male Special Forces soldiers were biopsied in m. vastus lateralis pre and post 8 days immobilizing restricted prone position. After immobilization, total mammalian target of rapamycin protein was reduced by 42% (P < 0.05), whereas total and phosphorylated protein levels of Akt, ribosomal protein S6k, 4E-BP1, and glycogen synthase kinase3ß were unchanged. Messenger RNA (mRNA) levels of the atrogenes forkhead box O3 (FoxO3), atrogin1, and muscle ring finger protein1 (MuRF1) increased by 36%, 53%, and 71% (P < 0.01), MuRF1 protein by 51% (P = 0.05), whereas FoxO1 and peroxisome proliferator-activated receptor γ coactivator-1 ß mRNAs decreased by 29% and 40% (P < 0.01). In conclusion, occupational immobilization in Special Forces soldiers led to modulations in molecular muscle mass regulators during 8 days prone SSR mission, which likely contribute to muscle loss observed in such operations. The present data expand our knowledge of human muscle mass regulation during short-term immobilization.

The influence of physical activity during youth on structural and functional properties of the Achilles tendon.

Achilles tendinopathy is a highly prevalent sports injury. Animal studies show a growth response in tendons in response to loading in the immature phase but not after puberty maturation. The aim of this investigation was to examine the structural and material properties in long distance runners who were either physically active (HAY) or inactive (LAY) in young age. Twelve men in HAY group and eight men in LAY group participated. Structural, functional, and biochemical properties of Achilles tendon were estimated from magnetic resonance imaging, ultrasound video recordings, mechanical tests, and tendon biopsies, respectively. There was no difference between the groups with respect to tendon cross-sectional area or tendon free length. There was no difference between the groups with respect to maximal force or mechanical properties. The collagen content, enzymatic and nonenzymatic cross-link density did not differ between the groups, nor did collagen fibril density, diameter, and area. There was a correlation between age and pentosidine/collagen within the groups [(HAY: P < 0.05 and r(2) = 0.47) and (LAY: P < 0.05 and r(2) = 0.52)]. The data suggest that high or low activity during youth did not appreciably influence the mechanical, structural, or biochemical properties of the Achilles tendon in adult long distance runners.

Physiological capacity and physical testing in male elite team handball.

AIM: The aim of the present study was to examine the physical demands placed on male elite team handball players in relation to playing position. METHODS: Male elite team handball field players were evaluated during match-play over a six season time span using physiological measurements and by subsequent physical testing. RESULTS: Mean heart rate and relative workload during match-play (N.=41) were 163 ± 5 beats·min⁻¹ (group means±SD) and 70.9 ± 6.0% of VO(2-max), respectively. Relative workload was lower (P<0.01) in the second half vs. the first (66.3 ± 5.9% vs. 75.4 ± 5.6% of VO(2-max)). Post-match blood lactate concentration was 4.8 ± 1.9 mM (range: 2.8-10.8 mM). Mean fluid loss was 0.81 ± 0.41 l pr. match. Mean VO(2max) was 5.18 ± 0.66 l O2·min-1 corresponding to 57.0 ± 4.1 mL O2·min⁻¹·kg⁻¹. Mean total running distance in the Yo-Yo intermittent recovery test (level 2) was 895 ± 184 m (range: 520-1360 m), which was greater in wing players (975 ± 123 m) than backcourt players (897 ± 108 m) and pivots (827 ± 264 m) (P<0.05). Fastest 30-m sprint time was 4.09 ± 0.12 s (range: 3.87-4.28 s). The repeated sprint test (7 x 30 m) yielded a mean fatigue index of -8.1 ± 2.7 %. Maximal jumping height in "Jump and Reach" testing was 0.71 ± 0.08 m (range: 0.61-0.86 m). Maximal ball throwing speed was observed using the set shot with 3-step run-up (92.8 ± 5.3 km·h⁻¹, range: 75.8-108.2 km·h⁻¹). CONCLUSION: Modern male elite team handball imposes moderate-to-high demands on the aerobic energy system and high demands on the anaerobic energy systems during certain periods of the match. Indications of temporary fatigue and a subsequent decline in performance were observed, since the relative workload decreased both in the first and in the second half of the match. Physiological profiles and physical test results differed between playing positions, with wing players covering a greater total distance in the Yo-Yo test and showing superior jumping performance and repeated sprint running capacity than backcourt players and pivots.

Stretch-shortening cycle muscle power in women and men aged 18-81 years: Influence of age and gender.

This study explored the age-related deterioration in stretch-shortening cycle (SSC) muscle power and concurrent force-velocity properties in women and men across the adult life span. A total of 315 participants (women: n = 188; men: n = 127) aged 18-81 years performed maximal countermovement jumps on an instrumented force plate. Maximal SSC leg extension power expressed per kg body mass (Ppeak) was greater in men than in women across the adult age span (P < 0.001); however, this gender difference was progressively reduced with increasing age, because men showed an ∼50% faster rate of decline in SSC power than women (P < 0.001). Velocity at peak power (VPpeak) was greater in men than in women (P < 0.001) but declined at a greater rate in men than in women (P = 0.002). Vertical ground reaction force at peak power (FPpeak) was higher in men than in women in younger adults only (P < 0.001) and the age-related decline was steeper in men than in women (P < 0.001). Men demonstrated a steeper rate of decline in Ppeak than women with progressive aging. This novel finding emerged as a result of greater age-related losses in men for both force and velocity. Consequently, maximal SSC power production was observed to converge between genders when approaching old age.

Effect of football or strength training on functional ability and physical performance in untrained old men.

The effects of 16 weeks of football or strength training on performance and functional ability were investigated in 26 (68.2 ± 3.2 years) untrained men randomized into a football (FG; n = 9), a strength training (ST; n = 9), or a control group (CO; n = 8). FG and ST trained 1.6 ± 0.1 and 1.5 ± 0.1 times per week, respectively, with higher (P < 0.05) average heart rate (HR) (∼140 vs 100 bpm) and time >90%HRmax (17 vs 0%) in FG than ST, and lower (P < 0.05) peak blood lactate in FG than ST (7.2 ± 0.9 vs 10.5 ± 0.6 mmol/L). After the intervention period (IP), VO2 max (15%; P < 0.001), cycle time to exhaustion (7%; P < 0.05), and Yo-Yo Intermittent Endurance Level 1 performance (43%; P < 0.01) were improved in FG, but unchanged in ST and CO. HR during walking was 12% and 10% lower (P < 0.05) in FG and ST, respectively, after IP. After IP, HR and blood lactate during jogging were 7% (P < 0.05) and 30% lower (P < 0.001) in FG, but unchanged in ST and CO. Sit-to-stand performance was improved (P < 0.01) by 29% in FG and 26% in ST, but not in CO. In conclusion, football and strength training for old men improves functional ability and physiological response to submaximal exercise, while football additionally elevates maximal aerobic fitness and exhaustive exercise performance.

Match performance and physiological capacity of female elite team handball players.

The present study evaluated the physical demands imposed on female elite team handball players in relation to playing position. Female elite team handball field players were examined during match-play over a 5-year period using video based computerized locomotion analysis of tournament matches. In addition, physiological measurements during match-play and in separate physical tests were carried out. A total distance of 4002±551 m (group means±SD) was covered per match with a total effective playing time of 50:42±5:50 min:s, while full-time players covered 4693±333 m. On average, each player (n=83) performed 663.8±99.7 activity changes per match, and the mean speed was 5.31±0.33 km · h(-1). High-intensity running constituted 0.8±0.5% of total effective playing time per match corresponding to 2.5±1.8% of the total distance covered. The amount of high-intensity running was reduced (p<0.05) 21.9% in the second half (44.9±16.8 m) compared to the first (57.5±21.3 m). Maximal oxygen uptake (VO2-max) was 3.49±0.37 l O2 · min(-1) corresponding to 49.6±4.8 ml O2 · min(-1) · kg(-1). Mean relative workload during match-play was 79.4±6.4% of VO2-max. Mean total running distance in the Yo-Yo intermittent recovery test (level 1) was 1436±222 m, which was greater in wing players (1516±172 m, p<0.05) than pivots (1360±118 m) and backcourt players (1352±148 m). In conclusion, modern female elite team handball is a physically demanding intermittent team sport, where players are exposed to high relative workloads with substantial estimated aerobic energy expenditure interspersed by short periods of dominant anaerobic energy production as reflected by the limited amount of high-intensity running. Indications of fatigue and a resulting decline in physical performance were identified, since the amount of high-intensity running and the relative workload levels decreased in the second half. Positional differences were observed, with wing players covering a greater total distance than backcourt players, performing more high-intensity running and demonstrating a better intermittent recovery capacity (Yo-Yo test outcome) compared to both backcourt players and pivots.

Ageing is associated with diminished muscle re-growth and myogenic precursor cell expansion early after immobility-induced atrophy in human skeletal muscle.

Recovery of skeletal muscle mass from immobilisation-induced atrophy is faster in young than older individuals, yet the cellular mechanisms remain unknown. We examined the cellular and molecular regulation of muscle recovery in young and older human subjects subsequent to 2 weeks of immobility-induced muscle atrophy. Retraining consisted of 4 weeks of supervised resistive exercise in 9 older (OM: mean age) 67.3, range 61-74 yrs) and 11 young (YM: mean age 24.4, range 21-30 yrs) males. Measures of myofibre area (MFA), Pax7-positive satellite cells (SCs) associated with type I and type II muscle fibres, as well as gene expression analysis of key growth and transcription factors associated with local skeletal muscle milieu, were performed after 2 weeks immobility (Imm) and following 3 days (+3d) and 4 weeks (+4wks) of retraining. OM demonstrated no detectable gains in MFA (vastus lateralis muscle) and no increases in number of Pax7-positive SCs following 4wks retraining, whereas YM increased their MFA (P < 0.05), number of Pax7-positive cells, and had more Pax7-positive cells per type II fibre than OM at +3d and +4wks (P < 0.05). No age-related differences were observed in mRNA expression of IGF-1Ea, MGF, MyoD1 and HGF with retraining, whereas myostatin expression levels were more down-regulated in YM compared to OM at +3d (P < 0.05). In conclusion, the diminished muscle re-growth after immobilisation in elderly humans was associated with a lesser response in satellite cell proliferation in combination with an age-specific regulation of myostatin. In contrast, expression of local growth factors did not seem to explain the age-related difference in muscle mass recovery.

Differences in tendon properties in elite badminton players with or without patellar tendinopathy.

The aim of this study was to examine the structural and mechanical properties of the patellar tendon in elite male badminton players with and without patellar tendinopathy. Seven players with unilateral patellar tendinopathy (PT group) on the lead extremity (used for forward lunge) and nine players with no current or previous patellar tendinopathy (CT group) were included. Magnetic resonance imaging was used to assess distal patellar tendon dimensions. Patellar tendon mechanical properties were assessed using simultaneous tendon force and deformation measurements. Distal tendon cross-sectional area (CSA) normalized for body weight (mm(2) /kg(2/3) ) was lower in the PT group compared with the CT group on both the non-lead extremity (6.1 ± 0.3 vs 7.4 ± 0.2, P < 0.05) and the lead extremity (6.5 ± 0.6 vs 8.4 ± 0.3, P < 0.05). Distal tendon stress was higher in the PT group compared with the CT group for both the non-lead extremity (31 ± 1 vs 27 ± 1 MPa, P < 0.05) and the lead extremity (32 ± 3 vs 21 ± 3 MPa, P < 0.01). Conclusively, the PT group had smaller distal patellar tendon CSA on both the injured (lead extremity) and the uninjured side (non-lead extremity) compared with the CT group. Subsequently, the smaller CSA yielded a greater distal patellar tendon stress in the PT group. Therefore, a small tendon CSA may predispose to the development of tendinopathy.

Slide-based ergometer rowing: effects on force production and neuromuscular activity.

Force production profile and neuromuscular activity during slide-based and stationary ergometer rowing at standardized submaximal power output were compared in 14 male and 8 female National Team rowers. Surface electromyography (EMG) was obtained in selected thoracic and leg muscles along with synchronous measurement of handle force and rate of force development (RFD). Compared to stationary conditions, slide-based peak force decreased by 76 (57-95) N (mean 95% CI) in males (P < 0.001) and 20 (8-31) N (P < 0.05) in females. Stroke rate increased (+10.7%) and late-phase RFD decreased (-20.7%) in males (P < 0.05). Neuromuscular activity in m. vastus lateralis decreased in the initial drive phase from 59% to 51% of EMG max in males and from 57% to 52% in females (P < 0.01-0.05), while also decreasing in the late recovery phase from 20% to 7% in males and 17% to 7% in females (P < 0.01). Peak force and maximal neuromuscular activity in the shoulder retractors always occurred in the second quartile of the drive phase. In conclusion, peak force and late-phase RFD (males) decreased and stroke rate increased (males) during slide-based compared to stationary ergometer rowing, potentially reducing the risk of overuse injury. Neuromuscular activity was more affected in leg muscles than thoracic muscles by slide-based ergometer rowing.

Locomotion characteristics and match-induced impairments in physical performance in male elite team handball players.

The purpose of this study was to determine the physical demands and match-induced impairments in physical performance in male elite Team Handball (TH) players in relation to playing position. Male elite TH field players were closely observed during 6 competitive seasons. Each player (wing players: WP, pivots: PV, backcourt players: BP) was evaluated during match-play using video recording and subsequently performing locomotion match analysis. A total distance of 3 627±568 m (group means±SD) was covered per match with a total effective playing time (TPT) of 53:51±5:52 min:s, while full-time players covered 3 945±538 m. The mean speed was 6.40±1.01 km · h - 1. High-intensity running constituted only 1.7±0.9% of TPT per match corresponding to 7.9±4.9% of the total distance covered. An average of 1 482.4±312.6 activity changes per player (n=82) with 53.2±14.1 high-intensity runs were observed per match. Total distance covered was greater in BP (3 765±532 m) and WP (3 641±501 m) than PV (3 295±495 m) (p<0.05), and WP performed more high-intensity running (10.9±5.7% of total distance covered) than PV (8.5±4.3%, p<0.05) and BP (6.2±3.2%, p<0.01). The amount of high-intensity running was lower (p<0.05) in the second (130.4±38.4 m) than in the first half (155.3±47.6 m) corresponding to a decrease of 16.2%.In conclusion, modern male elite TH is a complex team sport that comprises several types of movement categories, which during match-play place moderate-to-high demands on intermittent endurance running capacity and where the amount of high-intensity running may be high during brief periods of the match. Signs of fatigue-related changes were observed in terms of temporary impaired physical performance, since the amount of high-intensity running was reduced in the second half. Notably, physical demands differed between playing positions, with WP demonstrating a more intensive activity pattern than BP and PV, respectively.

Hormonal, immune, and oxidative stress responses to blood flow-restricted exercise.

INTRODUCTION: Heavy-load free-flow resistance exercise (HL-FFRE) is a widely used training modality. Recently, low-load blood-flow restricted resistance exercise (LL-BFRRE) has gained attention in both athletic and clinical settings as an alternative when conventional HL-FFRE is contraindicated or not tolerated. LL-BFRRE has been shown to result in physiological adaptations in muscle and connective tissue that are comparable to those induced by HL-FFRE. The underlying mechanisms remain unclear; however, evidence suggests that LL-BFRRE involves elevated metabolic stress compared to conventional free-flow resistance exercise (FFRE). AIM: The aim was to evaluate the initial (<10 min post-exercise), intermediate (10-20 min), and late (>30 min) hormonal, immune, and oxidative stress responses observed following acute sessions of LL-BFRRE compared to FFRE in healthy adults. METHODS: A systematic literature search of randomized and non-randomized studies was conducted in PubMed, Embase, Cochrane Central, CINAHL, and SPORTDiscus. The Cochrane Risk of Bias (RoB2, ROBINS-1) and TESTEX were used to evaluate risk of bias and study quality. Data extractions were based on mean change within groups. RESULTS: A total of 12525 hits were identified, of which 29 articles were included. LL-BFRRE demonstrated greater acute increases in growth hormone responses when compared to overall FFRE at intermediate (SMD 2.04; 95% CI 0.87, 3.22) and late (SMD 2.64; 95% CI 1.13, 4.16) post-exercise phases. LL-BFRRE also demonstrated greater increase in testosterone responses compared to late LL-FFRE. CONCLUSION: These results indicate that LL-BFRRE can induce increased or similar hormone and immune responses compared to LL-FFRE and HL-FFRE along with attenuated oxidative stress responses compared to HL-FFRE.

Recovery in mechanical muscle strength following resurfacing vs standard total hip arthroplasty - a randomised clinical trial.

OBJECTIVES: To evaluate the effect of resurfacing vs standard total hip replacement on post-surgery hip and knee muscle strength recovery in a prospective randomised controlled trial at the Department of Orthopaedics, University Hospital, Odense, Denmark. METHODS: Forty-three patients were randomised into (A) standard total hip arthroplasty (S-THA) and (B) resurfacing total hip arthroplasty (R-THA). Pre-surgery assessment and follow-up were conducted (8, 26 and 52 wks). Maximal isometric muscle strength (Nm) and between-limb asymmetry for the knee extensors/flexors, hip adductors/abductors, hip extensors/flexors were analysed. RESULTS: Maximal knee extensor and hip abductor strength were higher in S-THA than R-THA at 52 wks post-surgery (P ≤ 0.05) and hip extensors tended to be higher in S-THA at 52 wks (P = 0.06). All muscle groups showed substantial between-limb strength asymmetry (7-29%) with the affected side being weakest (P ≤ 0.05) and hip flexors being most affected. Asymmetry was present in half of the muscle groups at 26 wks (P ≤ 0.05), and remained present for the hip flexors and hip adductors at 52 wks (P ≤ 0.05). CONCLUSIONS: R-THA patients showed an attenuated and delayed recovery in maximal lower limb muscle strength (in 2/6 muscle groups) compared to S-THA. Notably, the attenuated strength recovery following R-THA was most markedly manifested in the late phase (1 yr) of post-surgical recovery, and appeared to be due to the detachment of the lower half of the gluteus maximus muscle rather than implant design per se. Thus, the present data failed to support the hypothesis that R-THA would result in an enhanced strength rehabilitation compared to S-THA. Further, between-limb asymmetry remained present for hip flexors and adductors after 52 wks. TRIAL REGISTRATION: NCT01229293.

Changes in muscle strength and morphology after muscle unloading in Special Forces missions.

The purpose of the present study was to determine the changes in maximal muscle strength, rapid force capacity, jumping performance and muscle morphology following a Special Forces military operation involving 8 days of muscle unloading. Nine male Special Forces soldiers were tested before (pre) and immediately after (post1) an 8-day simulated special support and reconnaissance (SSR) mission and after 3 h of active recovery (post2). Maximal muscle strength (MVC) and rate of force development (RFD) were measured along with maximal counter movement jump height (JH). Muscle biopsies were obtained from the vastus lateralis at pre and post1. Acute reductions were found in MVC (11%), JH (10%) and RFD (17-22%) after 8 days of muscle unloading (post1) (P≤0.05). Type IIX fiber type area% increased (P≤0.05) at post1 together with a tendency toward increased type IIX fiber type % (P=0.09) and decreased type I fiber type % (P=0.06), suggesting a transition toward a less fatigue-resistant fiber-type profile. In conclusion, short-term unloading during SSR missions led to marked reductions in mechanical muscle function and functional performance, which may be partly explained by the changes in muscle morphology. Future studies should identify intervention strategies to counter-act the observed impairments.

Acute fatigue impairs neuromuscular activity of anterior cruciate ligament-agonist muscles in female team handball players.

In sports, like team handball, fatigue has been associated with an increased risk of anterior cruciate ligament (ACL) injury. While effects of fatigue on muscle function are commonly assessed during maximal isometric voluntary contraction (MVC), such measurements may not relate to the muscle function during match play. The purpose of this study was to investigate the effect of muscle fatigue induced by a simulated handball match on neuromuscular strategy during a functional sidecutting movement, associated with the incidence of ACL injury. Fourteen female team handball players were tested for neuromuscular activity [electromyography (EMG)] during a sidecutting maneuver on a force plate, pre and post a simulated handball match. MVC was obtained during maximal isometric quadriceps and hamstring contraction. The simulated handball match consisted of exercises mimicking handball match activity. Whereas the simulated handball match induced a decrease in MVC strength for both the quadriceps and hamstring muscles (P<0.05), a selective decrease in hamstring neuromuscular activity was seen during sidecutting (P<0.05). This study shows impaired ACL-agonist muscle (i.e. hamstring) activity during sidecutting in response to acute fatigue induced by handball match play. Thus, screening procedures should involve functional movements to reveal specific fatigue-induced deficits in ACL-agonist muscle activation during high-risk phases of match play.