Countermovement Jump and Drop Jump Performances Are Related to Grand Jeté Leap Performance in Dancers With Different Skill Levels.

ABSTRACT: Blanco, P, Nimphius, S, Seitz, LB, Spiteri, T, and Haff, GG. Countermovement jump and drop jump performances are related to grand jeté leap performance in dancers with different skill levels. J Strength Cond Res 35(12): 3386-3393, 2021-Thirty-five classical ballet dancers were chosen to investigate relationships between the grand jeté leap, countermovement jump (CMJ), and drop jump (DJ) and establish whether the magnitude of the relationship between these tests differed across 3 skill levels. Subjects (male: n = 11 and female: n = 24) were divided into 3 groups: novice (n = 12; age: 16.6 ± 1.5 years; height: 1.7 ± 0.1 m; body mass: 58.0 ± 13.0 kg), semiprofessional (n = 13; age: 20.0 ± 1.6 years; height: 1.7 ± 0.1 m; body mass: 64.1 ± 10.5 kg), and professional (n = 10; age: 23.8 ± 3.5 years; height: 1.8 ± 1.2 m; body mass: 63.3 ± 14.7 kg). Grand jeté leap height, followed by CMJ and DJ vertical displacement, was assessed. Significant relationships were found between the grand jeté, CMJ (r = 0.77, p = 0.001) and DJ (r = 0.76, p = 0.001). After a Fisher's r-z transformation, professional dancers and novice dancers showed greater r-value differences in CMJ (r2 - r1 = 0.27) compared with novice (r2 - r1 = 0.17) and semiprofessional dancers (r2 - r1 = 0.11), indicating larger strength of CMJ to grand jeté relationship in professionals. The grand jeté leap showed large to very large correlations with CMJ and DJ within groups. These common performance tests were determined to be practical and efficient methods for assessing the jumping ability of dancers. As dance skill increased, larger correlations were observed, suggesting that dancers with superior ballet skills may be more likely to use their underpinning physical capacities to jump higher within the context of ballet-specific jumping.

Evidence for a New Compact Symmetric Fission Mode in Light Thorium Isotopes.

Taking benefit of the R3B/SOFIA setup to measure the mass and the nuclear charge of both fission fragments in coincidence with the total prompt-neutron multiplicity, the scission configurations are inferred along the thorium chain, from the asymmetric fission in the heavier isotopes to the symmetric fission in the neutron-deficient thorium. Against all expectations, the symmetric scission in the light thorium isotopes shows a compact configuration, which is in total contrast to what is known in the fission of the heavier thorium isotopes and heavier actinides. This new main symmetric scission mode is characterized by a significant drop in deformation energy of the fission fragments of about 19 MeV, compared to the well-known symmetric scission in the uranium-plutonium region.

Clavicular osteotomy in complicated revision of total shoulder arthroplasty: indications, surgical technique, and outcomes.

PURPOSE: Adequate exposure in revision of total shoulder arthroplasty (TSA) is important for optimal prosthesis placement and functional results. A clavicular osteotomy in difficult cases of revision TSA is a useful surgical technique that increases the superior exposure area, provides safer dissection, minimizes damage to the anterior deltoid muscle, improves glenoid access, and allows for superior dislocation of the humeral component. There is a paucity of literature analyzing the clavicular osteotomy during challenging cases of revision TSA. The aims of this study were to describe the application, surgical technique, and outcomes of revision TSA with a clavicular osteotomy. METHODS: This was a retrospective study of consecutive patients who underwent revision TSA with a clavicle osteotomy at a single institution (2004-2016). A curved longitudinal clavicular osteotomy is created parallel to the origin of the anterior deltoid muscle. This allows for lateral reflection of the osteotomy and anterior deltoid muscle to significantly increase superior exposure and reduce damage to remaining deltoid muscle fibres. Osteotomy closure is simple with four or five Nice knot osteosutures. The Constant-Murley score and osteotomy healing were assessed at every follow-up. All complications were reviewed. RESULTS: Forty patients who had a mean age of 63.8 years (range 37-87) at time of surgery and mean follow-up duration of 34 months (range 12-88) were analyzed. Pre-operative Constant-Murley scores improved significantly from 32 ± 19.0 to 58 ± 15.0 (p < 0.001) at one year and 65 ± 13.1 (p < 0.001) at two years. Primary osteotomy healing and callus formation were evident in 95% of cases by three months. Five patients developed post-operative complications (13%) related to the clavicular osteotomy: three mid-diaphyseal clavicular fractures sustained after trauma (8%), one clavicular stress fracture (3%), and case of one loosening (3%). Three patients (8%) required surgical revision of the osteotomy (two internal fixation and one revision osteosuturing). No neurovascular injuries or scapular fractures were encountered. CONCLUSION: A curved longitudinal clavicular osteotomy is beneficial in difficult revision TSA and is another tool in the arsenal of experienced shoulder surgeons who manage these challenging cases. This surgical technique increases glenoid exposure, facilitates superior dislocation of the humeral component, minimizes anterior deltoid damage, and reduces the risk of neurovascular injuries. All clavicular complications occurred within four months prior to osteotomy union, with many sustained due to trauma. However, patients who developed a complication had comparable shoulder function as those without.

Spontaneous sensations reveal distorted body perception in complex regional pain syndrome (CRPS).

Distortions of body representation have been reported in Complex Regional Pain Syndrome (CRPS). The perception of sensations arising without external triggers (spontaneous sensations or SPS) was assessed here as a means of investigating distortions of body representation and awareness in CRPS. To avoid confounds between CRPS symptoms and SPS, lower-limb CRPS patients were included, whereas SPS were tested on the hands. Patients and controls were required to focus on their hands and to report the spatial and qualitative characteristics of SPS arising there. We found an ipsilateral decrease in the perception of thermal, pain-related and surface/mechanical SPS, as well as in the number of SPS-sensitive areas. The latter finding was predicted by decreased body awareness as assessed through questionnaires. A bilateral decrease in the perception of paresis-like SPS was also observed. Finally, the ipsilateral spatial distribution of SPS frequency and intensity underwent a shift from the fingers towards the lower parts of the palm. CRPS is likely to distort patient's body perception and awareness of the entire half-body ipsilateral to the affected limb, and even of both sides. Such disturbances are not manifested solely as a decrease in sensitivity, but sometimes as shifts in the spatial distribution of sensitivity.

Passive muscle stretching impairs rapid force production and neuromuscular function in human plantar flexors.

PURPOSE: We examined the effect of muscle stretching on the ability to produce rapid torque and the mechanisms underpinning the changes. METHODS: Eighteen men performed three conditions: (1) continuous stretch (1 set of 5 min), (2) intermittent stretch (5 sets of 1 min with 15-s inter-stretch interval), and (3) control. Isometric plantar flexor rate of torque development was measured during explosive maximal voluntary contractions (MVC) in the intervals 0-100 ms (RTDV100) and 0-200 ms (RTDV200), and in electrically evoked 0.5-s tetanic contractions (20 Hz, 20 Hz preceded by a doublet and 80 Hz). The rate of EMG rise, electromechanical delay during MVC (EMDV) and during a single twitch contraction (EMDtwitch) were assessed. RESULTS: RTDV200 was decreased (P < 0.05) immediately after continuous (- 15%) and intermittent stretch (- 30%) with no differences between protocols. The rate of torque development during tetanic stimulations was reduced (P < 0.05) immediately after continuous (- 8%) and intermittent stretch (- 10%), when averaged across stimulation frequencies. Lateral gastrocnemius rate of EMG rise was reduced after intermittent stretch (- 27%), and changes in triceps surae rate of EMG rise were correlated with changes in RTDV200 after both continuous (r = 0.64) and intermittent stretch (r = 0.65). EMDV increased immediately (31%) and 15 min (17%) after intermittent stretch and was correlated with changes in RTDV200 (r = - 0.56). EMDtwitch increased immediately after continuous (4%), and immediately (5.4%), 15 min (6.3%), and 30 min after (6.4%) intermittent stretch (P < 0.05). CONCLUSIONS: Reductions in the rate of torque development immediately after stretching were associated with both neural and mechanical mechanisms.

Combining higher-load and lower-load resistance training exercises: A systematic review and meta-analysis of findings from complex training studies.

OBJECTIVES: The aim of the present meta-analytical review was to determine the effectiveness of training programmes combining higher-load and lower-load exercises in one workout (i.e. complex training [CT]) on lower-body performance. DESIGN: Systematic review and meta-analysis. METHODS: A search of five electronic databases (PubMed, Web of Science, SportDiscus, CINAHL and Scopus) was conducted to identify all publications up to 7 March 2018. Meta-analyses were performed using a random-effects model with the dependent variables countermovement jump (CMJ) height, squat jump (SJ) height, one-repetition maximum (1-RM) squat performance and sprint time for 5m, 10m, 20m, 30m and 40m, respectively. RESULTS: The analysis comprised 33 studies and a total of 1064 healthy participants. The meta-analysis revealed that CT is effective in improving CMJ (95% confidence interval [CI] 5.6%-12.3%), SJ (95% CI 8.0%-17.4%), 1-RM squat (95% CI 16.4%-30.7%) and sprint performance (5m=95% CI -14.8% to -0.9%, 10m=95% CI -6.0% to -2.1%, 20m=95% CI -7.4% to -1.4%, 30m=95% CI -8.0% to -0.6%). However, when directly compared to traditional training methods, only 1-RM squat strength performance and 20m sprint time were superior following CT interventions (95% CI 0.2%-13.7% and 95% CI -1.6% to -0.1%, respectively) CONCLUSIONS: CT is an acceptable method for improving jump, strength and sprint performance in athletes. Compared to traditional training methods, CT seems to produce superior training effects only for 1-RM squat and 20m sprint performance; however, these findings were influenced by single studies and should be therefore interpreted with circumspection.

Acute Effects of Back Squats on Countermovement Jump Performance Across Multiple Sets of a Contrast Training Protocol in Resistance-Trained Men.

Bauer, P, Sansone, P, Mitter, B, Makivic, B, Seitz, LB, and Tschan, H. Acute effects of back squats on countermovement jump performance across multiple sets of a contrast training protocol in resistance-trained men. J Strength Cond Res 33(4): 995-1000, 2019-This study was designed to evaluate the voluntary postactivation potentiation (PAP) effects of moderate-intensity (MI) or high-intensity (HI) back squat exercises on countermovement jump (CMJ) performance across multiple sets of a contrast training protocol. Sixty resistance-trained male subjects (age, 23.3 ± 3.3 years; body mass, 86.0 ± 13.9 kg; and parallel back squat 1-repetition maximum [1-RM], 155.2 ± 30.0 kg) participated in a randomized, crossover study. After familiarization, the subjects visited the laboratory on 3 separate occasions. They performed a contrast PAP protocol comprising 3 sets of either MI (6 × 60% of 1-RM) or HI back squats (4 × 90% of 1-RM) or 20 seconds of recovery (CTRL) alternated with 7 CMJs that were performed at 15 seconds, and 1, 3, 5, 7, 9 and 11 minutes after the back squats or recovery. Jump height and relative peak power output recorded with a force platform during MI and HI conditions were compared with those recorded during control condition to calculate the voluntary PAP effect. Countermovement jump performance was decreased immediately after the squats but increased across all 3 sets of MI and HI between 3 and 7 minutes after recovery. However, voluntary PAP effects were small or trivial, and no difference between the 3 sets could be found. These findings demonstrate that practitioners can use MI and HI back squats to potentiate CMJs across a contrast training protocol, but a minimum of 3 minutes of recovery after the squats is needed to benefit from voluntary PAP.

Variable, but not free-weight, resistance back squat exercise potentiates jump performance following a comprehensive task-specific warm-up.

Studies examining acute, high-speed movement performance enhancement following intense muscular contractions (frequently called "post-activation potentiation"; PAP) often impose a limited warm-up, compromizing external validity. In the present study, the effects on countermovement vertical jump (CMJ) performance of back squat exercises performed with or without elastic bands during warm-up were compared. After familiarization, fifteen active men visited the laboratory on two occasions under randomized, counterbalanced experimental squat warm-up conditions: (a) free-weight resistance (FWR) and (b) variable resistance (VR). After completing a comprehensive task-specific warm-up, three maximal CMJs were performed followed by three back squat repetitions completed at 85% of 1-RM using either FWR or VR Three CMJs were then performed 30 seconds, 4 minutes, 8 minutes, and 12 minutes later. During CMJ trials, hip, knee, and ankle joint kinematics, ground reaction force data and vastus medialis, vastus lateralis, and gluteus maximus electromyograms (EMG) were recorded simultaneously using 3D motion analysis, force platform, and EMG techniques, respectively. No change in any variable occurred after FWR (P > 0.05). Significant increases (P < 0.05) were detected at all time points following VR in CMJ height (5.3%-6.5%), peak power (4.4%-5.9%), rate of force development (12.9%-19.1%), peak concentric knee angular velocity (3.1%-4.1%), and mean concentric vastus lateralis EMG activity (27.5%-33.4%). The lack of effect of the free-weight conditioning contractions suggests that the comprehensive task-specific warm-up routine mitigated any further performance augmentation. However, the improved CMJ performance following the use of elastic bands is indicative that specific alterations in force-time properties of warm-up exercises may further improve performance.

Arthroplasty for glenohumeral arthritis in shoulders with a previous Bristow or Latarjet procedure.

BACKGROUND: Coracoid transfer has become increasingly popular for recurrent anterior shoulder instability. Despite the success, glenohumeral arthropathy develops in some patients. Arthroplasty in this population is complicated by altered anatomy, scarring, and retained hardware. This study evaluated shoulder arthroplasty in patients with a previous Latarjet or Bristow procedure. METHODS: Between 1980 and 2014, 33 patients underwent shoulder arthroplasty after coracoid transfer. Of these, 17 men and 13 women were monitored for a minimum of 2 years or until reoperation. Arthroplasty procedures included hemiarthroplasty (HA) in 5, total shoulder arthroplasty (TSA) in 14, and reverse shoulder arthroplasty (RTSA) in 11. Outcome measures included pain, range of motion, complications, and reoperations. RESULTS: At the most recent follow-up, pain had significantly improved in all arthroplasty groups. Elevation and external rotation also improved significantly (P < .001). Overall, 9 shoulders (30%) underwent revision for instability (1 TSA and 1 HA), glenoid loosening (1 TSA), instability and glenoid loosening (3 TSA), late cuff failure (1 TSA), and painful glenoid erosion (2 HA). Revision rates were significantly different between HA and RTSA (P = .0058) and between TSA and RTSA (P = .015). Radiographically, 2 additional anatomic glenoid components were considered loose, progressive medial erosion was seen in 1 HA, and grade 1 to 2 notching was observed in 2 RTSAs. CONCLUSIONS: Shoulder arthroplasty in patients after prior coracoid transfer is technically challenging, yet improvements in pain and function are predictable. Instability and glenoid loosening are common reasons for revision surgery, likely related to difficulties in achieving a good soft tissue balance.

Bony Reconstruction of the Anterior Glenoid Rim.

Recurrent anterior shoulder instability is associated with glenohumeral bone loss. Glenoid deficiency compromises the concavity-compression mechanism. Medial Hill-Sachs lesions can result in an off-track humeral position. Anterior glenoid reconstruction or augmentation prevents recurrence by addressing the pathomechanics. In Bristow and Latarjet procedures, the coracoid process is harvested for conjoint tendon transfer, capsular reinforcement, and glenoid rim restoration. Complications and the nonanatomic nature of the procedure have spurred research on graft sources. The iliac crest is preferred for autogenous structural grafts. Tricortical, bicortical, and J-bone grafts have shown promising results despite the historical association of Eden-Hybinette procedures with early degenerative joint disease. Allogeneic osteochondral grafts may minimize the risk of arthropathy and donor site morbidity. Tibial plafond and glenoid allografts more closely match the native glenoid geometry and restore the articular chondral environment, compared with conventional grafts. Graft availability, cost, risk of disease transmission, and low chondrocyte viability have slowed the acceptance of osteochondral allografts.

Hip thrust-based PAP effects on sprint performance of soccer players: heavy-loaded versus optimum-power development protocols.

This study aimed to investigate the acute effects of two barbell hip thrust-based post-activation potentiation (PAP) protocols on subsequent sprint performance. Using a crossover design, eighteen soccer athletes performed 5 m, 10 m, and 20 m sprints before and 15 s, 4 min, and 8 min after two PAP protocols. The PAP conditioning activities consisted of hip thrust exercises loaded with either 85% 1RM or a load for optimum power development. The resulting 5 m and 10 m sprint performances were impaired at 15 s following both protocols. At 4 min and 8 min, meaningful improvements were observed for the three sprint distances following both of the protocols. Meaningful differences were found when comparing the two PAPs over time: greater impairments in 5 m and 10 m following the 85% of 1 RM protocol after 15 s, and greater improvements in all sprint distances after 4 min and 8 min following the optimum power development protocol. Positive correlations between the hip thrust's 1RM and power values and the overall individual PAP responses were found. This investigation showed that both heavy-loaded and optimum-power hip thrust exercises can induce a PAP response, with the optimum-power development protocol preferred due its higher efficiency.

Influence of screw type and length on fixation of anterior glenoid bone grafts.

BACKGROUND: Bone-grafting procedures for recurrent shoulder instability produce low recurrence rates, although they are associated with complications such as graft non-union. Inadequate screw purchase is considered to play a causative role. However, excessive screw length can endanger neurovascular structures. The present study aimed to investigate how type and length of screws influences construct rigidity in a simplified glenoid model. METHODS: Testing was performed on composite polyurethane foam models with material properties and abstract dimensions of a deficient glenoid and an bone graft. Three screw types (cannulated 3.75 mm and 3.5 mm and solid 4.5 mm) secured the graft in a bicortical-bicortical, bicortical-unicortical and unicortical-unicortical configuration. Biomechanical testing consisted of applying axial loads when measuring graft displacement. RESULTS: At 200 N, graft displacement reached 0.74 mm, 0.27 mm and 0.24 mm for the unicortical-unicortical and 0.40 mm, 0.25 mm and 0.24 mm for the unicortical-bicortical configuration of the 3.75 mm, 3.5 mm and 4.5 mm screw types. The 3.75 mm screw incurred significant displacements in the unicortical configurations compared to the bicortical-bicortical method (p < 0.001). CONCLUSIONS: The present study demonstrates that common screw types resist physiological shear loads in a bicortical configuration. However, the 3.75 mm screws incurred significant displacements at 200 N in the unicortical configurations. These findings have implications regarding hardware selection for bone-grafting procedures.

Restoration of Articular Geometry Using Current Graft Options for Large Glenoid Bone Defects in Anterior Shoulder Instability.

PURPOSE: The purpose of this cadaveric study was to compare standard and modified coracoid transfer procedures, bicortical and tricortical iliac crest autografts, and tibial plafond and glenoid allografts with respect to glenoid surface curvature restoration. METHODS: Computed tomography scans of 8 cadaveric shoulders were acquired in 9 conditions: (1) intact, (2) 25% width defect, (3) classic Latarjet, (4) modified congruent-arc Latarjet, (5) tricortical iliac crest inner table, (6) outer table, (7) bicortical iliac crest, (8) distal tibia, and (9) glenoid allograft. Outcome measures included articular surface area, width, depth, axial and coronal radius of curvature, and subchondral articular step-off, analyzed in bone and soft-tissue window. RESULTS: Reconstruction of the articular surface area was optimal with the glenoid allograft (99.4%), classic Latarjet (97.4%), and iliac crest bicortical graft (93.2%). Depth was best restored by the congruent-arc Latarjet (101.0%), tibial (98.9%), and glenoid (95.3%) allografts. Axial curvature was closely matched by the glenoid allograft (97.5%), classic Latarjet (108.7%), and iliac bicortical graft (91.2%). Coronal curvature was most accurately restored by the glenoid allograft (102.6%), the tibial allograft (115.0%), and the classic Latarjet (55.9%). The articular step-off was smallest using the glenoid allograft. CONCLUSIONS: Overall, glenoid allografts most accurately restored articular geometry. Alternative grafts provided restoration of some parameters but not others. Classic Latarjet performed well in axial and coronal curvature on average but exhibited large variability. Tibial allograft produced the poorest results in axial curvature, despite excellent coronal curvature reconstruction. The congruent-arc Latarjet did not restore the axial curvature accurately and overcorrected coronal curvature. Graft geometry must be weighed against availability, morbidity, and the role of additional stabilizers. CLINICAL RELEVANCE: Accurate graft morphology may help prevent postoperative osteoarthritis. Grafts differ significantly regarding geometric parameters. The findings of this study will help surgeons select the most appropriate graft for glenoid reconstruction.

Atypical permanent neurological sequelae after an acute intoxication with lithium and aripiprazole.

OBJECTIVES: The aim of the present case report was to describe atypical neurological sequelae after a lithium and aripiprazole co-intoxication in a suicide attempt. METHODS: We report the case of a 31-year-old patient with bipolar disorder who developed, after lithium and aripiprazole massive ingestion, a severe pseudobulbar dysarthria and motor disorders suggestive of basal ganglia micro lesions. We review literature on neurological sequelae due to acute lithium intoxications. RESULTS: Acute lithium intoxication can cause permanent neurological sequelae, the most frequent clinical feature being a permanent cerebellar syndrome. Moreover, the widely-prescribed combination of lithium with antipsychotics increases the neurotoxicity in lithium intoxications. In this case, both atypical neurological syndrome and normal paraclinical investigations lead first to misdiagnose the lithium neurological damages. CONCLUSIONS: This case illustrates that acute lithium intoxications can result in serious and potentially permanent neurological deficits, which remain difficult to diagnose. Imaging abnormalities are not constant, and neurological presentation can be atypical.

Investigation of the predictive validity of laser-EPs in normal, UVB-inflamed and capsaicin-irritated skin with four analgesic compounds in healthy volunteers.

AIMS: The aim of the present study was to assess the predictivity of laser-(radiant-heat)-evoked potentials (LEPs) from the vertex electroencephalogram, using an algesimetric procedure, testing the anti-nociceptive/anti-hyperalgesic effects of single oral doses of four marketed analgesics (of different compound classes) vs. placebo, in healthy volunteers with three skin types. METHODS: This was a randomized, placebo-controlled, single-blind, five-way-crossover trial. Twenty-five healthy male/female Caucasians were included (receiving celecoxib 200 mg, pregabalin 150 mg, duloxetine 60 mg, lacosamide 100 mg or placebo) in a Williams design, with CO2 laser-induced painful stimuli to normal, ultraviolet (UV) B-inflamed and capsaicin-irritated skin. LEPs and visual analogue scale ratings were taken at baseline and hourly for 6 h postdose from all three skin types. RESULTS: In normal skin, the averaged postdose LEP peak-to-peak-(PtP)-amplitudes were reduced by pregabalin (-2.68 µV; 95% confidence interval (CI) -4.16, 1.19) and duloxetine (-1.73 µV; 95% CI -3.21, -0.26) but not by lacosamide and celecoxib vs. placebo. On UVB-irradiated skin, reflecting inflammatory pain, celecoxib induced a pronounced reduction in LEP PtP amplitudes vs. placebo (-6.2 µV; 95% CI -7.88, -4.51), with a smaller reduction by duloxetine (-4.54 µV; 95% CI -6.21, -2.87) and pregabalin (-3.72 µV; 95% CI -5.40, -2.04), whereas lacosamide was inactive. LEP PtP amplitudes on capsaicin-irritated skin, reflecting peripheral/spinal sensitization, as in neuropathic pain, were reduced by pregabalin (-3.78 µV; 95% CI -5.31, -2.25) and duloxetine (-2.32 µV; 95% CI -3.82, -0.82) but not by celecoxib or lacosamide vs. placebo, which was in agreement with known clinical profiles. Overall, PtP amplitude reductions were in agreement with subjective ratings. CONCLUSIONS: LEP algesimetry is sensitive to analgesics with different modes of action and may enable the effects of novel analgesics to be assessed during early clinical development.

A sled push stimulus potentiates subsequent 20-m sprint performance.

OBJECTIVES: The objective of this study was to examine the potentiating effects of performing a single sprint-style sled push on subsequent unresisted 20m sprint performance. DESIGN: Randomized crossover design. METHODS: Following a familiarization session, twenty rugby league players performed maximal unresisted 20m sprints before and 15s, 4, 8 and 12min after a single sled push stimulus loaded with either 75 or 125% body mass. The two sled push conditions were performed in a randomized order over a one-week period. The fastest sprint time recorded before each sled push was compared to that recorded at each time point after to determine the post-activation potentiation (PAP) effect. RESULTS: After the 75% body mass sled push, sprint time was 0.26±1.03% slower at the 15s time point (effect size [ES]=0.07) but faster at the 4 (-0.95±2.00%; ES=-0.22), 8 (-1.80±1.43%; ES=-0.42) and 12 (-1.54±1.54%; ES=-0.36)min time points. Sprint time was slower at all the time points after the 125% body mass sled (1.36±2.36%-2.59±2.90%; ESs=0.34-0.64). CONCLUSIONS: Twenty-meter sprint performance is potentiated 4-12min following a sled push loaded with 75% body mass while it is impaired after a 125% body mass sled. These results are of great importance for coaches seeking to potentiate sprint performance with the sled push exercise.

Variable Resistance Training Promotes Greater Strength and Power Adaptations Than Traditional Resistance Training in Elite Youth Rugby League Players.

Rivière, M, Louit, L, Strokosch, A, and Seitz, LB. Variable resistance training promotes greater strength and power adaptations than traditional resistance training in elite youth rugby league players. J Strength Cond Res 31(4): 947-955, 2017-The purpose of this study was to examine the strength, velocity, and power adaptations in youth rugby league players in response to a variable resistance training (VRT) or traditional free-weight resistance training (TRAD) intervention. Sixteen elite youth players were assigned to a VRT or TRAD group and completed 2 weekly upper- and lower-body strength and power sessions for 6 weeks. Training programs were identical except that the VRT group trained the bench press exercise with 20% of the prescribed load coming from elastic bands. Bench press 1 repetition maximum (1RM) and bench press mean velocity and power at 35, 45, 65, 75, and 85% of 1RM were measured before and after the training intervention, and the magnitude of the changes was determined using effect sizes (ESs). The VRT group experienced larger increases in both absolute (ES = 0.46 vs. 0.20) and relative (ES = 0.41 vs. 0.19) bench press 1RM. Similar results were observed for mean velocity as well as both absolute and relative mean power at 35, 45, 65, 75, and 85% of 1RM. Furthermore, both groups experienced large gains in both velocity and power in the heavier loads but small improvements in the lighter loads. The improvements in both velocity and power against the heavier loads were larger for the VRT group, whereas smaller differences existed between the 2 groups in the lighter loads. Variable resistance training using elastic bands may offer a greater training stimulus than traditional free-weight resistance training to improve upper-body strength, velocity, and power in elite youth rugby league players.

Chain-loaded variable resistance warm-up improves free-weight maximal back squat performance.

The acute influence of chain-loaded variable resistance exercise on subsequent free-weight one-repetition maximum (1-RM) back squat performance was examined in 16 recreationally active men. The participants performed either a free-weight resistance (FWR) or chain-loaded resistance (CLR) back squat warm-up at 85% 1-RM on two separate occasions. After a 5-min rest, the participants attempted a free-weight 1-RM back squat; if successful, subsequent 5% load additions were made until participants failed to complete the lift. During the 1-RM trials, 3D knee joint kinematics and knee extensor and flexor electromyograms (EMG) were recorded simultaneously. Significantly greater 1-RM (6.2 ± 5.0%; p < .01) and mean eccentric knee extensor EMG (32.2 ± 6.7%; p < .01) were found after the CLR warm-up compared to the FWR condition. However, no difference (p > .05) was found in concentric EMG, eccentric or concentric knee angular velocity, or peak knee flexion angle. Performing a CLR warm-up enhanced subsequent free-weight 1-RM performance without changes in knee flexion angle or eccentric and concentric knee angular velocities; thus a real 1-RM increase was achieved as the mechanics of the lift were not altered. These results are indicative of a potentiating effect of CLR in a warm-up, which may benefit athletes in tasks where high-level strength is required.