Increased training load promotes sleep propensity and slow-wave sleep in endurance runners: Can a high-heat-capacity mattress topper modulate this effect?

The present study aimed to: (1) investigate sleep architecture in response to an overload training and taper periods among endurance runners; and (2) assess the sleep benefits of a high-heat-capacity mattress topper. Twenty-one trained male endurance runners performed a 2-week usual training regimen (baseline) followed by 2-week overload and taper periods. From overload to the end of the taper period, they were assigned into two groups based on the mattress topper used: high-heat-capacity mattress topper (n = 11) or low-heat-capacity mattress topper (n = 10). Training load was assessed daily using the session rating of perceived exertion. Following each period, sleep was monitored by polysomnography, and nocturnal core body temperature was recorded throughout the night. Irrespective of the group, awakening episodes > 5 min decreased following overload compared with baseline (-0.48, p = 0.05). Independently of mattress topper, each 100 A.U. increase in 7-day training load prior to polysomnographic recording was associated with higher slow-wave sleep proportion (ß = +0.13%; p = 0.05), lower sleep-onset latency (ß = -0.49 min; p = 0.05), and a reduction in the probability of transition from N1 sleep stage to wakefulness (ß = -0.12%; p = 0.05). Sleeping on a high-heat-capacity mattress topper did not affect any sleep variable compared with a low-heat-capacity mattress topper. Increased training loads promote slow-wave sleep and sleep propensity, highlighting the adaptative nature of sleep to diurnal activity and the role of sleep in physiological recovery. Further studies are required on the potential benefits of high-heat-capacity mattress toppers on sleep architecture among athletes.

Cold-water immersion and whole-body cryotherapy attenuate muscle soreness during 3 days of match-like tennis protocol.

PURPOSE: This study aimed to investigate the effect of whole-body cryotherapy (WBC), cold-water immersion (CWI) and passive recovery (PAS) on tennis recovery. METHODS: Thirteen competitive male tennis players completed three consecutive match-like tennis protocols, followed by recovery (WBC, CWI, PAS) in a crossover design. Five tennis drills and serves were performed using a ball machine to standardize the fatiguing protocol. Maximal voluntary contraction (MVC) peak torque, creatine kinase activity (CK), muscle soreness, ball accuracy and velocity together with voluntary activation, low- and high-frequency torque and EMG activity were recorded before each protocol and 24 h following the third protocol. RESULTS: MVC peak torque (- 7.7 ± 11.3%; p = 0.001) and the high- to low-frequency torque ratio (- 10.0 ± 25.8%; p < 0.05) decreased on Day 1 but returned to baseline on Day 2, Day 3 and Day 4 (p = 0.052, all p > 0.06). The CK activity slightly increased from 161.0 ± 100.2 to 226.0 ± 106.7 UA L-1 on Day 1 (p = 0.001) and stayed at this level (p = 0.016) across days with no differences between recovery interventions. Muscle soreness increased across days with PAS recovery (p = 0.005), while no main effect of time was neither observed with WBC nor CWI (all p > 0.292). The technical performance was maintained across protocols with WBC and PAS, while it increased for CWI on Day 3 vs Day 1 (p = 0.017). CONCLUSION: Our 1.5-h tennis protocol led to mild muscle damage, though neither the neuromuscular function nor the tennis performance was altered due to accumulated workload induced by consecutive tennis protocols. The muscle soreness resulting from tennis protocols was similarly alleviated by both CWI and WBC. TRIAL REGISTRATION: IRB No. 2017-A02255-48, 12/05/2017.

Higher training loads affect sleep in endurance runners: Can a high-heat-capacity mattress topper mitigate negative effects?

This study investigates the impact of a training program on sleep among endurance runners and the benefits of chronically using a high-heat-capacity mattress topper (HMT). Twenty-one trained male athletes performed a 2-week usual training regimen, sleeping on a Low-heat-capacity Mattress Topper (LMT), followed by 2-week overload and taper periods. From overload, participants were assigned into two groups based on the mattress topper used: HMT (n = 11) or LMT (n = 10). Irrespective of the group, overload increased general stress and stress-reaction symptoms evaluated by questionnaires, with no decline in performance on a graded-exercise treadmill test, the majority of participant being "non-overreached" (n = 14). From a daily perspective, each additional 100 A.U. in training load, assessed using the session rating of perceived exertion, was associated with an impairment in subsequent sleep efficiency (ß = -0.2%; p < 0.01), wake after sleep onset (ß = +0.4 min; p < 0.05) and sleep onset latency (ß = +0.5 min; p < 0.05), which was unaffected by HMT use. Practitioners should be aware of sleep needs, especially during excessive training loads, whereas implementing individualised sleep strategies. Further studies should be conducted on potential benefits of HMT among athletes in various sleep conditions.

Faster early rate of force development in warmer muscle: an in vivo exploration of fascicle dynamics and muscle-tendon mechanical properties.

Although heat exposure has been shown to increase the skeletal rate of force development (RFD), the underlying processes remain unknown. This study investigated the effect of heat on gastrocnemius medialis (GM) muscle-tendon properties and interactions. Sixteen subjects performed electrically evoked and voluntary contractions combined with ultrafast ultrasound under thermoneutral [control (CON): 25.8 ± 1.8°C, core temperature 37.0 ± 0.3°C, muscle temperature 34.0 ± 1.1°C] and passive heat exposure [hot (HOT): 47.4 ± 1.8°C, core temperature 38.4 ± 0.3°C, muscle temperature 37.0 ± 0.8°C] conditions. Maximal voluntary force changes did not reach statistical significance (-5.0 ± 11.3%, P = 0.052) whereas voluntary activation significantly decreased (-4.6 ± 8.7%, P = 0.038) in HOT. Heat exposure significantly increased voluntary RFD before 100 ms from contraction onset (+48.2 ± 62.7%; P = 0.013), without further changes after 100 ms. GM fascicle dynamics during electrically evoked and voluntary contractions remained unchanged between conditions. Joint velocity at a given force was higher in HOT (+7.1 ± 6.6%; P = 0.004) but the fascicle force-velocity relationship remained unchanged. Passive muscle stiffness and active tendon stiffness were lower in HOT than CON (P ≤ 0.030). This study showed that heat-induced increases in early voluntary RFD may not be attributed to changes in contractile properties. Late voluntary RFD was unaltered, possibly due to decreased soft tissues' stiffness in heat. Further investigations are required to explore the influence of neural drive and motor unit recruitment in the enhancement of explosive strength elicited by heat exposure.

Sprint Acceleration Mechanical Outputs Derived from Position- or Velocity-Time Data: A Multi-System Comparison Study.

To directly compare five commonly used on-field systems (motorized linear encoder, laser, radar, global positioning system, and timing gates) during sprint acceleration to (i) measure velocity−time data, (ii) compute the main associated force−velocity variables, and (iii) assess their respective inter-trial reliability. Eighteen participants performed three 40 m sprints, during which five systems were used to simultaneously and separately record the body center of the mass horizontal position or velocity over time. Horizontal force−velocity mechanical outputs for the two best trials were computed following an inverse dynamic model and based on an exponential fitting of the position- or velocity-time data. Between the five systems, the maximal running velocity was close (7.99 to 8.04 m.s−1), while the time constant showed larger differences (1.18 to 1.29 s). Concurrent validity results overall showed a relative systematic error of 0.86 to 2.28% for maximum and theoretically maximal velocity variables and 4.78 to 12.9% for early acceleration variables. The inter-trial reliability showed low coefficients of variation (all <5.74%), and was very close between all of the systems. All of the systems tested here can be considered relevant to measure the maximal velocity and compute the force−velocity mechanical outputs. Practitioners are advised to interpret the data obtained with either of these systems in light of these results.

Effects of a 14-Day High-Intensity Shock Microcycle in High-Level Ice Hockey Players' Fitness.

ABSTRACT: Brocherie, F, Perez, J, and Guilhem, G. Effects of a 14-day high-intensity shock microcycle in high-level ice hockey players' fitness. J Strength Cond Res 36(8): 2247-2252, 2022-Elite athletes face congested schedules with increased competition frequency and restricted time for training periods. Therefore, time is lacking to design long-term sport-specific block periodization. This study aimed to investigate the effects of adding a 14-day off-ice high-intensity training (HIT) shock microcycle to the usual training content of the pre-season preparation of high-level male ice hockey players' fitness. Fourteen players were randomly assigned to off-ice HIT ( n = 7) or usual pre-season training (control, n = 7). For the HIT group, additional off-ice training content included 2 sessions of repeated-maximal resistance training, 2 sessions of repeated-sprint training, and 2 sessions of high-intensity intermittent training. Control group performed equal number of off-ice sessions using traditional strength and conditioning training. Off-ice Yo-Yo intermittent recovery test level 2 (YYIR2) and on-ice repeated-sprint ability test (RSA) were conducted before (pre-test) and 3 days after the intervention (post-test). Statistical significance was set at p < 0.05. Significant group × time interactions were found for off-ice YYIR2 performance ( p < 0.05) and on-ice RSA-cumulated skating time (RSA TT ; p < 0.05). Compared with pre-test, off-ice YYIR2 distance covered significantly increased (from 708.6 ± 97.2 to 885.7 ± 118.7 m, p < 0.01; +25.8 ± 16.9%, p < 0.05) and on-ice RSA TT significantly decreased (from 28.35 ± 0.87 to 28.14 ± 0.84 seconds; -1.7 ± 2.1%, both p < 0.05)] for HIT group. No significant pre-test to post-test changes were found for the control group (+2.7 ± 20.0% for YYIR2 and +0.9 ± 2.2% for RSA TT ). The implementation of a 14-day shock microcycle (including 6 HIT sessions) significantly improved fitness performance in high-level male ice hockey players. Such HIT block periodization offers a promising way to deal with congested schedules.

Ice Hockey Forward Skating Force-Velocity Profiling Using Single Unloaded vs. Multiple Loaded Methods.

ABSTRACT: Perez, J, Guilhem, G, and Brocherie, F. Ice hockey forward skating force-velocity profiling using single unloaded vs. multiple loaded methods. J Strength Cond Res 36(11): 3229-3233, 2022-This study aimed to compare skating force-velocity relationships determined throughout sprints performed against various loaded conditions or inferred from movement kinetics measured during a single unloaded sprint. Ten female ice hockey players performed one unloaded maximal skating sprint test measured with a radar gun followed by 4 resisted skating sprints against a robotic horizontal resistance with progressive loads in reference to equipped body mass (BM): 3 kg (robotic resistance), 25, 50, and 75% of equipped BM. Maximal theoretical force (F 0 ), velocity (V 0 ), power (P max ), optimal velocity (V opt ) condition for producing maximal power, and slope of the linear force-velocity relationship (SFV) were determined from each method and compared using a paired sample t -test, absolute mean bias (±95% confidence intervals), Pearson correlations, and typical error of the estimate in standardized units (effect size [ES]). Statistical significance was set at p < 0.05. No statistical difference was found for all mechanical variables determined from the 2 methods ( p ranging 0.09-0.59). Although exhibiting positive correlations ranging from moderate ( r = 0.50 for SFV) to high ( r ranging from 0.71 to 0.84 for F 0 , V 0 , V opt , and P max ) between methods, all variables exhibited large levels of error between approaches (ES ranging 0.66-1.71). Multiple loaded and single unloaded methods were comparable with determine force-velocity relationships during forward on-ice skating sprint. The low-cost fatigue-free unloaded method suggests it could be used in constrained contexts (i.e., congested schedule and low available time) or for a simple force-velocity profiling. Inversely, multiple loaded methods would be more appropriate to evaluate and individualize training for skilled ice hockey players accustomed to resistive skating sprint.

International matches elicit stable mechanical workload in high-level female ice hockey.

This study aimed to quantify in- and between-match characteristics and mechanical workload variations elicited by a congested schedule in high-level female ice hockey. Six players were monitored during four international pre-season exhibition matches against the same opponent. Two different methods (Player Load and Accel'Rate) were used to assess specific mechanical workload. Number of shifts and effective playing time per shift were significantly higher for period 2 (p = 0.03 for both). Mechanical workload intensity (i.e., relative and peak workload) showed a significant (p ≤ 0.05) decrease from period 1 to period 2 and period 3 (moderate-to-large Cohen's d). All workload variables remained stable between matches (p > 0.25). Team variability showed good-to-moderate CVs (< 10%) for all variables for in- and between-match variability. Accumulated workload computed with the Player Load method was threefold higher compared to the Accel'Rate method (+ 87.8% mean difference; large Cohen's d). These findings demonstrate that high-level female ice hockey-specific mechanical workload declines with reduced high-intensity output across periods, while it remains stable between matches against standardized opposition. This study strongly suggests that the present workload metrics could be used to determine the mechanical demand elicited by matches played against various opponents in real game conditions.

The ballistic hip thrust test: a potential tool to monitor neuromuscular performance.

To investigate the reliability of the ballistic hip thrust (BHT) test performed on force plates as a diagnostic tool to monitor posterior chain neuromuscular status and compare its usefulness with the counter movement jump (CMJ). Twenty-two male football players from an elite Under-19 French Ligue 1 football club (16.4 ± 0.6 years) performed two assessments; Assessment 1: Two testing sessions separated by one week were performed to assess the reliability of the test. Participants performed a 3-set workout of 4 repetitions of the BHTs each session. Intra-day (between set) and inter-day (between testing day) reliability of concentric mean force, takeoff peak force and peak power were assessed. Assessment 2: Participants performed a 1-set workout of 3 repetitions of the CMJ and 4 repetitions of the BHT tests pre- and post-training to compare the usefulness of both tests. Concentric mean force and takeoff peak force showed small-to-moderate standardised typical errors (TE: 0.2-0.7) for inter- and intra-day reliability. Inter-day concentric mean force showed a coefficient of variation (CV) of 7.2%. Intra-day concentric mean force and take-off peak force showed a CV of 4.2% and 5.5%. BHT and CMJ showed similar moderate levels of usefulness. The BHT test showed moderate levels of reliability and usefulness. This test could be a useful addition to a testing battery to monitor posterior chain neuromuscular status.

Comparison of A Single Vibration Foam Rolling and Static Stretching Exercise on the Muscle Function and Mechanical Properties of the Hamstring Muscles.

Knee extension and hip flexion range of motion (ROM) and functional performance of the hamstrings are of great importance in many sports. The aim of this study was to investigate if static stretching (SS) or vibration foam rolling (VFR) induce greater changes in ROM, functional performance, and stiffness of the hamstring muscles. Twenty-five male volunteers were tested on two appointments and were randomly assigned either to a 2 min bout of SS or VFR. ROM, counter movement jump (CMJ) height, maximum voluntary isometric contraction (MVIC) peak torque, passive resistive torque (PRT), and shear modulus of semitendinosus (ST), semimembranosus (SM), and biceps femoris (BFlh), were assessed before and after the intervention. In both groups ROM increased (SS = 7.7%, P < 0.01; VFR = 8.8%, P < 0.01). The MVIC values decreased after SS (-5.1%, P < 0.01) only. Shear modulus of the ST changed for -6.7% in both groups (VFR: P < 0.01; SS: P < 0.01). Shear modulus decreased in SM after VFR (-6.5%; P = 0.03) and no changes were observed in the BFlh in any group (VFR = -1%; SS = -2.9%). PRT and CMJ values did not change following any interventions. Our findings suggest that VFR might be a favorable warm-up routine if the goal is to acutely increase ROM without compromising functional performance.

A comparison of foam rolling and vibration foam rolling on the quadriceps muscle function and mechanical properties.

PURPOSE: The purpose of the study was to investigate the effects of using a vibration foam roll (VFR) or a non-vibration foam roll (NVFR) on maximum voluntary isometric contraction peak torque (MVIC), range of motion (ROM), passive resistive torque (PRT), and shear modulus. METHODS: Twenty-one male volunteers visited the laboratory on two separate days and were randomly assigned to either a VFR group or a NVFR group. Both interventions were performed for 3 × 1 min each. Before and after each intervention, passive resistive torque and maximum voluntary isometric contraction peak torque of the leg extensors were assessed with a dynamometer. Hip extension ROM was assessed using a modified Thomas test with 3D-motion caption. Muscle shear modulus of the vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) was assessed with shear wave elastography (SWE). RESULTS: In both groups (VFR, NVFR) we observed an increase in MVIC peak torque (+ 14.2 Nm, + 8.6 Nm) and a decrease in shear modulus of the RF (- 7.2 kPa, - 4.7 kPa). However, an increase in hip extension ROM (3.3°) was only observed in the VFR group. There was no change in PRT and shear modulus of the VL and VM, in both the VFR group and the NVFR group. Our findings demonstrate a muscle-specific acute decrease in passive RF stiffness after VFR and NVFR, with an effect on joint flexibility found only after VFR. CONCLUSION: The findings of this study suggest that VFR might be a more efficient approach to maximize performance in sports with flexibility demands.

A Novel Accelerometry-Based Metric to Improve Estimation of Whole-Body Mechanical Load.

While the Player Load is a widely-used parameter for physical demand quantification using wearable accelerometers, its calculation is subjected to potential errors related to rotational changes of the reference frame. The aims of this study were (i) to assess the concurrent validity of accelerometry-based Player Load against force plates; (ii) to validate a novel metric, the Accel'Rate overcoming this theoretical issue. Twenty-one recreational athlete males instrumented with two triaxial accelerometers positioned at the upper and lower back performed running-based locomotor movements at low and high intensity over six in-series force plates. We examined the validity of the Player Load and the Accel'Rate by using force plates. Standard error of the estimate was small to moderate for all tested conditions (Player Load: 0.45 to 0.87; Accel'Rate: 0.25 to 0.95). Accel'Rate displayed trivial to small mean biases (-1.0 to 6.1 a.u.) while the Player Load displayed systematic very large to extremely large mean biases (17.1 to 226.0 a.u.). These findings demonstrate a better concurrent validity of the Accel'Rate compared to the Player Load. This metric could be used to improve the estimation of whole-body mechanical load, easily accessible in sport training and competition settings.

Hamstring muscle elasticity differs in specialized high-performance athletes.

The effect of training on hamstring flexibility has been widely assessed through the measurement of the maximal range of motion or passive torque. However, these global measures do not provide direct information on the passive muscle mechanical properties of individual muscle. This characterization is crucial to better understand the effect of interventions as selective adaptations may occur among synergist muscles. Taking advantage of shear wave elastography, we aimed to determine whether elite sport athletes exhibit different passive shear modulus of hamstring heads compared to controls. Passive shear modulus was measured on semitendinosus (ST), semimembranosus (SM), and biceps femoris (BF) using shear wave elastography with the knee flexed at 60° and 90°, and 90° of hip flexion. A total of 97 elite athletes from various sports including running sprint, figure skating, fencing, field hockey, taekwondo, basketball, and soccer and 12 controls were evaluated. The shear modulus measured at 60° of knee flexion was lower in SM for figure skating (P < .001; d = 1.8), taekwondo (P < .001; d = 2.1), fencing (P = .024; d = 1.0), and soccer (P = .011; d = 0.9) compared to controls, while no difference was found for athletic sprinters, field hockey, and basketball players. Shear modulus of the BF and ST muscle was not significantly different between controls and elite athletes, regardless of the sport specialization (all P values = 1). We provide evidence that the shear modulus of the SM is altered in athletes involved in elite sport practice performed over large range of motion and/or including substantial stretching program in training content (taekwondo, figure skating, fencing, and soccer).

Surface properties affect the interplay between fascicles and tendinous tissues during landing.

PURPOSE: Muscle-tendon units are forcefully stretched during rapid deceleration events such as landing. Consequently, tendons act as shock absorbers by buffering the negative work produced by muscle fascicles likely to prevent muscle damage. Landing surface properties can also modulate the amount of energy dissipated by the body, potentially effecting injury risk. This study aimed to evaluate the influence of three different surfaces on the muscle-tendon interactions of gastrocnemius medialis (GM), and vastus lateralis (VL) during single- and double-leg landings from 50 cm. METHODS: Ultrasound images, muscle activity and joint kinematics were collected for 12 participants. Surface testing was also performed, revealing large differences in mechanical behavior. RESULTS: During single-leg landing, stiffer surfaces increased VL fascicle lengthening and velocity, and muscle activity independent of joint kinematics while GM length changes showed no difference between surfaces. Double-leg landing resulted in similar fascicle and tendon behavior despite greater knee flexion angles on stiffer surfaces. CONCLUSION: This demonstrates that VL fascicle lengthening is greater when the surface stiffness increases, when performing single-leg landing. This is due to the combination of limited knee joint flexion and lower surface absorption ability which resulted in greater mechanical demand mainly withstood by fascicles. GM muscle-tendon interactions remain similar between landing surfaces and types. Together, this suggests that surface damping properties primarily affect the VL muscle-tendon unit with a potentially higher risk of injury as a result of increased surface stiffness when performing single-leg landing tasks.

Influence of fascicle strain and corticospinal excitability during eccentric contractions on force loss.

NEW FINDINGS: What is the central question of this study? Do neural and/or mechanical factors determine the extent of muscle damage induced by eccentric contractions? What is the main finding and its importance? The extent of muscle damage induced by eccentric contractions is related to both mechanical strain and corticospinal excitability measured at long muscle lengths during eccentric contractions. ABSTRACT: In this study, we investigated whether the mechanical and neural characteristics of maximal voluntary eccentric contractions would determine the extent of change in postexercise maximal voluntary isometric contraction (MVC) torque and muscle soreness. Eleven men performed 10 sets of 15 isokinetic (45 deg s-1 ) maximal voluntary eccentric knee extensions. Knee-extension torque and vastus lateralis fascicle length were assessed at sets 1, 5 and 9. Vastus lateralis motor evoked potential, maximal M wave (MEP/M) and the cortical silent period (CSP) were measured at 75 and 100 deg of knee flexion (0 deg = full extension) during contractions and were normalized to MEP/M (MEP/Mecc/iso ) and CSP (CSPecc/iso ) recorded during isometric MVC at each angle. The MVC torque and muscle soreness of the knee extensors were assessed before, 24, 48 and 96 h after the eccentric contractions. The extent of relative decrease in MVC torque at 24 h postexercise (r2  = 0.38) and peak muscle soreness (r2  = 0.69) were correlated (P < 0.05) with MEP/Mecc/iso measured at 100 deg, but not at 75 deg. The average torque on the descending limb of the torque-angle relationship (r2  = 0.16), fascicle elongation (r2  = 0.18) and CSPecc/iso at both 75 (r2  = 0.00) and 100 deg (r2  = 0.02) were not significantly correlated with the relative decrease in MVC torque. The relative decrease in MVC torque was best predicted by a combination of mean torque on the descending limb, fascicle elongation and MEP/Mecc/iso (R2  = 0.93). It is concluded that the extent of muscle damage based on the reduction in MVC torque is determined by mechanical strain and corticospinal excitability at long muscle lengths during maximal voluntary eccentric contractions.

Interactions between fascicles and tendinous tissues in gastrocnemius medialis and vastus lateralis during drop landing.

Animal tendons have been shown to act as shock absorbers to protect muscle fascicles from exercise-induced damage during landing tasks. Meanwhile, the contribution of tendinous tissues to damping activities such as landing has been less explored in humans. The aim of this study was to analyze in vivo fascicle-tendon interactions during drop landing to better understand their role in energy dissipation. Ultrafast ultrasound images of the gastrocnemius medialis (GM) and vastus lateralis (VL), lower limb electromyographic activity, 2-D kinematics, and ground reaction forces were collected from twelve participants during single- and double-leg drop landings from various heights. For both muscles, length changes were higher in tendinous tissues than in fascicles, demonstrating their key role in protecting fascicles from rapid active lengthening. Increasing landing height increased lengthening and peak lengthening velocity of VL fascicle and GM architectural gear ratio, whereas GM fascicle displayed similar length and velocity patterns. Single-leg landing lengthens the tendinous tissues of GM and, to a greater degree, VL muscles, without affecting the fascicles. These findings demonstrate the adjustment in fascicle-tendon interactions to withstand mechanical demand through the tendon buffer action and fascicle rotation. The higher VL fascicle contribution to negative work as the drop height increases would suggest muscle-specific damping responses during drop landing. This can originate from the distal-to-proximal sequence of joint kinetics, from differences in muscle and tendon functions (one- and two-joint muscles), architectural and morphological properties (eg, tendon stiffness), as well as from the muscle activity of the GM and VL muscles.

Case Study: Sleep and Injury in Elite Soccer-A Mixed Method Approach.

Nédélec, M, Leduc, C, Dawson, B, Guilhem, G, and Dupont, G. Case study: sleep and injury in elite soccer. A mixed method approach. J Strength Cond Res 33(11): 3085-3091, 2019-This case study allowed an examination of the link between sleep and injury occurrence in an elite male soccer player competing in French League 1 and Union of European Football Associations matches. During 4 months, a mixed method approach was used, combining actigraphic sleep assessment with qualitative interviews on a daily basis. Three injuries were reported over the study period. Sleep onset latency (SOL), both in the single night (117 ± 43 minutes) and in the week (78 ± 50 minutes) before injury occurrence, was longer than preseason baseline values (18 ± 13 minutes; effect size (ES): 3.1 and 1.6, respectively). Similarly, sleep efficiency in the single night (73 ± 7%) and the week (75 ± 7%) before injury occurrence was lower than baseline (90 ± 3%; ES: 3.2 and 2.8, respectively). In this case study, SOL and efficiency were altered on the night and in the week before injury occurrence. Individualized assessment of sleep during congested playing schedules may be useful to aid in preventing injury occurrence.

The slack test does not assess maximal shortening velocity of muscle fascicles in humans.

The application of a series of extremely high accelerative motor-driven quick releases while muscles contract isometrically (i.e. slack test) has been proposed to assess unloaded velocity in human muscle. This study aimed to measure gastrocnemius medialis fascicle shortening velocity (VF) and tendinous tissue shortening velocity during motor-driven quick releases performed at various activation levels to assess the applicability of the slack test in humans. Gastrocnemius medialis peak VF and joint velocity recorded from 25 participants using high frame rate ultrasound during quick releases (at activation levels from 0% to 60% of maximal voluntary isometric torque) and during fast contractions without external load (ballistic condition) were compared. Unloaded joint velocity calculated using the slack test method increased whereas VF decreased with muscle activation level (P≤0.03). Passive and low-level quick releases elicited higher VF values (≥41.8±10.7 cm s-1) compared with the ballistic condition (36.3±8.7 cm s-1), while quick releases applied at 60% of maximal voluntary isometric torque produced the lowest VF These findings suggest that initial fascicle length, complex fascicle-tendon interactions, unloading reflex and motor-driven movement pattern strongly influence and limit the shortening velocity achieved during the slack test. Furthermore, VF elicited by quick releases is likely to reflect substantial contributions of passive processes. Therefore, the slack test is not appropriate to assess maximal muscle shortening velocity in vivo.

Specific joint angle dependency of voluntary activation during eccentric knee extensions.

INTRODUCTION: This study compared voluntary activation during isometric, concentric, and eccentric maximal knee extensions at different joint angles. METHODS: Fifteen participants performed isometric, concentric, and eccentric protocols (9 contractions each). For each protocol, the central activation ratio (CAR) was randomly measured at 50°, 75°, or 100° of knee joint angle (0° = full knee extension) using superimposed supramaximal paired nerve stimulations during contractions. RESULTS: CAR increased between 50° and 100° during isometric (93.6 ± 3.1 vs. 98.5 ± 1.4%), concentric (92.4 ± 5.4 vs. 99.2 ± 1.2%), and eccentric (93.0 ± 3.5 vs. 96.6 ± 3.8%) contractions. CAR was lower during eccentric than both isometric and concentric contractions at 75° and 100°, but similar between contraction types at 50°. CONCLUSIONS: The ability to activate muscle maximally is impaired during eccentric contractions compared with other contraction types at 75° and 100°, but not at 50°. Muscle Nerve 56: 750-758, 2017.

Muscle fascicle shortening behaviour of vastus lateralis during a maximal force-velocity test.

PURPOSE: Muscle fascicles-tendon interactions are the main determinant in production of high joint velocity. Currently, no study has investigated the muscle fascicles behaviour of knee extensor muscles until the highest reachable velocity (e.g., unloaded knee extension). We aimed to track the changes in vastus lateralis fascicles length during knee extensions to quantify muscle fascicles and tendinous tissues contributions to muscle-tendon unit shortening and to determine maximal muscle fascicles shortening velocity. METHODS: Fifteen participants performed isokinetic and isoinertial knee extensions, and ultrafast ultrasound imaging was used to observe the vastus lateralis fascicles from low to very high joint velocity. RESULTS: The muscle fascicles shortening velocity increased linearly with the increase in knee joint velocity up to the maximal joint velocity (mean R 2 = 0.93 ± 0.08). Muscle fascicles contribution to muscle-tendon unit shortening velocity was almost constant regardless of the condition (83 ± 23%). Using Hill's equation, the maximal velocity of knee joint and muscle fascicles was determined at 1000 ± 489°s-1 and 5.1 ± 2.0 L0 s-1 (47.4 ± 18.7 cm s-1), respectively. CONCLUSIONS: Contribution of muscle fascicles to the muscle-tendon unit shortening velocity was much higher for the vastus lateralis in this study compared to the gastrocnemius medialis in two previous studies. Moreover, this contribution of muscle fascicles shortening velocity was constant whatever the velocity condition, even at the highest reachable velocity. Thus, the vastus lateralis fascicles shortening velocity increases linearly with the knee joint velocity until high velocities and its behaviour strongly accorded with the classical Hill's force-velocity relationship.