Muscular Power Output Research Articles

The Effects of Mental Fatigue Induced by the Stroop Test on Muscular Endurance Performance and Neuromuscular Activation in Division III Female Athletes

The purpose of this study was to investigate the effect that mental fatigue, as induced by a Stroop test, has on resistance training performance outcomes such as muscular endurance, power output, and neuromuscular activation. Seven female college-aged NCAA Division III student-athletes with at least one year of resistance training experience and were within the 50th percentile for maximal aerobic capacity provided informed consent for participation. During two separate visits, using a within-subject crossover experimental design, subjects completed either the experimental or control condition. Subjects then completed a to-failure leg press test at 50% of their 1-repetition maximum (1RM) followed by an isometric midthigh pull (IMTP) attempt with electromyography (EMG) analysis. The experimental condition consisted of a 30-minute Stroop test, while the control condition consisted of watching 30 minutes of a sitcom. Both activities were completed while cycling at 40% of their aerobic capacity. A NASA Task Load Index (TLX) inventory was administered following the completion of each cycling session to determine the perceived workload and mental fatigue of each activity. While the mentally fatiguing condition was significantly more mentally fatiguing (p = 0.02) than the control condition, mental fatigue did not statistically affect any of the evaluated performance outcomes (p>0.05). These findings suggest that mental fatigue, a common symptom of psychological stress, does not affect resistance-training-related performance outcomes among female athletic populations.

Ten-minute warm-up in hot climate best assists thermal comfort, muscular power output, and fatigue, during soccer-specific repeated-sprint ability.

Structuring warm-up (WU) in hot climate conditions before high-intensity efforts is still drawing the attention of researchers and practitioners. The present study investigates the effect of two WU durations (i.e.10 min: WU10 and 20 min: WU20) in a hot climate (~31°C), on thermal comfort, muscular power output and fatigue after a repeated-sprint test (RSA) in soccer players. Twelve amateur soccer players (age = 21.13 ± 1.8 years; height = 172.5 ± 4.6 cm and weight = 70.8 ± 5.1 kg) participated in a cross-over randomized study, and they underwent a soccer-specific RSA test, after two WU durations and on different days. Peak power (PP), mean power (MP) and the fatigue index (FI) were calculated and analysed. Likewise, thermal comfort/discomfort (TC), tympanic temperature (Ttym) and rating of perceived exertion (RPE) were recorded at rest, after WU and after RSA. The ANOVA showed a significant increase in MP after WU10 in comparison to WU20 by 1.9%, while PP remained similar between the two durations. A significant decline in muscular power in WU20 compared to WU10 appeared from the 5th sprinting repetition and continued to the end of the RSA. The WU20, compared to the WU10, produced higher RPE at post-WU (p < 0.001) and post-RSA (p = 0.018), and higher thermal discomfort sensation in both post-WU (p = 0.022) and post-RSA (p = 0.007) point of measures. Larger increases in Ttym were recorded after WU20 compared to WU10. WU10 in a hot climate (~31°C) best assists mean power output during soccer RSA, but not peak power. Extending the WU duration up to 20 min in a hot climate was revealed to be detrimental for muscular power output, inducing excessive thermal discomfort and fatigue. Therefore, it is important that trainers and soccer players carefully consider WU duration prior to competitions and training sessions in a hot climate, to optimize physiological responses.

Resistance exercise intervention on muscular strength and power, and functional capacity in acute hospitalized older adults: a systematic review and meta-analysis of 2498 patients in 7 randomized clinical trials.

To date, no meta-analytical study evaluating the benefits of resistance exercise intervention on muscular strength and power and functional capacity in acute hospitalized older adults was conducted. Then, to synthesize the emerging evidence on the effects of resistance exercise intervention on muscular strength and power and functional capacity in acute hospitalized older adults, two independent authors performed a systematic search (PubMed, Scopus, Web of Science, and SciELO) until January 2021. Randomized clinical trials were included regarding the effects of resistance exercise and hospital usual care. The Cochrane Collaboration assessment tool was used to analyze the risk of bias. The comparisons included muscular strength (isometric handgrip strength and one-repetition maximum test of leg press), muscular power (output during leg press exercise), and functional capacity (timed-up-and-go, and short physical performance battery). Resistance exercise intervention increased muscular strength (isometric handgrip strength: mean difference = 2.50kg, 95% confidence interval (CI) = 1.33, 3.67; and one-repetition maximum test of leg press: mean difference = 19.28kg, 95% confidence interval = 14.70, 23.86) and muscular power (mean difference = 29.52W, 95% confidence interval = 28.84, 30.21), and functional capacity (timed-up-and-go: mean difference = 3.40s, 95% confidence interval = 0.47, 6.36; and short physical performance battery: mean difference = 1.29 points, 95% confidence interval = 0.10, 2.48) at discharge compared with hospital usual care. This meta-analysis endorses the increase of muscular strength and power gains and improving the functional capacity in favor of resistance exercise intervention in acute hospitalized older adults. TRIAL REGISTRATION : https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42020203658.

Warm-up durations in a hot-dry climate affect thermoregulation, mean power-output and fatigue, but not peak power in specific soccer repeated-sprint ability

BackgroundThis study addressed the lack of data on the effect of warm-up (WU) duration in hot-dry climate (~ 30 °C; ~ 18% RH), on thermoregulation, muscular power-output, and fatigue after specific soccer repeated-sprint test (RSA).MethodsEleven amateur soccer players participated in a cross-over randomized study and they underwent the Bangsbo repeated-sprint test, after three WU durations (i.e. WU10, WU15 and WU20 min) at 70% of MAV, and on different days. Peak power (PP), mean power (MP) and the fatigue index (FI) were recorded and analyzed. Likewise, heart rate (HR), tympanic temperature (Ttym), mean body temperature (MBT) and rating of perceived exertion (RPE) were recorded during each session.ResultsThe repeated measure ANOVA showed that MP improved after WU15 in comparison to WU10 and WU20 (p = 0.04 and p = 0.001; respectively). Nonetheless, no significant effect on PP was recorded after all WU durations. FI during RSA increased after WU20 in comparison to WU15 and WU10 (p < 0.001 and p = 0.003; respectively). Higher RPE values (p < 0.001) were recorded after WU15 and WU20 in comparison to WU10 duration. The two-way ANOVA showed higher ΔTtym and ΔMBT values after WU15 and WU20 compared to WU10 (p = 0.039 and p < 0.001for Ttym; p = 0.005 and p < 0.001 for MBT, respectively).ConclusionsThe WU15 at 70% of MAV better assists mean power-output during soccer RSA in hot-dry (~ 30 °C; 18% RH) climate, but not peak power. Reducing WU duration up to 10 min seems to be insufficient to induce beneficial physiological changes necessary for optimizing repeated-sprint performance, while its extension up to 20 min remains detrimental for muscular power and induces higher fatigue.

Transfer of Dry-Land Resistance Training Modalities to Swimming Performance.

A great number of studies focusing on the effects of dry-land resistance training interventions on swimming performance remain inconclusive. It is suggested that transferability of dry-land strength gains to swimming performance appear when dry-land resistance training programs are swim-specific. The main aim of this study was to compare the effects of specific dry-land resistance training on an ergometer with traditional dry-land exercises, and to determine how much of the resistance training effects were transferred to specific swimming conditions. The study included a group of 26 youth competitive male swimmers (age 15.7 ± 0.5 years, height 174.6 ± 6.6 cm, weight 68.4 ± 8.2 kg, training experience 5.8±0.7 years) of regional level. They were randomly allocated to one of two groups: experimental (E) and control (T). Both groups were involved in a 12-week dry-land resistance training concentrated on increasing muscular strength and power output of the upper limbs. Group E used a specialized ergometer (JBA – Zbigniew Staniak), while group T performed traditional resistance exercises. The program consisted of 10 sets of 30 s of exercise with 30 s rest intervals between each set. A two-way repeated measures ANOVA with Tukey HSD post hoc comparisons was used to determine if any significant differences existed between training groups across pretest and posttest conditions. The significance level was set at p ≤ 0.05. Dry-land resistance training modalities were the only differences in training between both groups. Our findings show that rates of transfer are much higher in group E than in group T, which resulted in a significant increase in swimming velocity (by 4.32%, p<0.001; ES=1.23, and 2.78%, p<0.003, ES=0.31, respectively).

Effect of Eccentric Cycling and Plyometric Training on Physiological and Performance Related Parameters of Trained Junior Track Cyclists

Abstract Introduction. Some certain well-established training protocols exist for developing physical and physiological demands of a track cyclist. But still there is controversy on the effectiveness of combined training protocols. The present study was aimed to investigate the effects of 4-week concurrent eccentric cycling and plyometric training on cycling performance of male cyclists at the pre-competitive phase. Material and methods. A paired study design was applied to 15 young (15.04 ± 1.01 yrs) Indian male track cyclists to assess the effects of proposed concurrent training protocol on body composition and various physical fitness parameters. Results. Hydration status [TBW (~1%) and ICW (~1%)], glycogen content (~3%), muscular strength (~6-11%), trunk flexibility (~5%), anaerobic power output (~9%), endurance capacity (~5%), acceleration (~7%), leg explosive strength (~7%) and agility (~2%) were found to be improved significantly after the 4-week concurrent training protocol. Conclusions. The concurrent intervening physical training protocol was intended to increase muscular hypertrophy, peripheral factor gradient, glycolytic and oxidative enzyme capacity with proper neuromuscular coordination which may ultimately help the cyclists to pedal at a faster rate with higher muscular power output even for longer time.

Yoga Breathing Techniques Have No Impact on Isokinetic and Isoinertial Power.

Wooten, SV, Cherup, N, Mazzei, N, Patel, S, Mooney, K, Rafiq, A, and Signorile, JF. Yoga breathing techniques have no impact on isokinetic and isoinertial power. J Strength Cond Res 34(2): 430-439, 2020-As an exercise discipline, yoga incorporates breathing (pranayama) and posture (asana) techniques to facilitate improvements in flexibility, strength, and meditation. Both techniques have been used to enhance muscular strength and power output. The purpose of this study was to determine the effects of various yoga breathing techniques on lower-limb power output. Thirty-two individuals (15 men and 17 women) participated in the study. All subjects performed a baseline 1 repetition maximum (1RM) on a pneumatic leg press machine and isokinetic testing on a Biodex 4 dynamometer. Participants then performed 3RM power tests at 50% of 1RM on the pneumatic leg press machine using 3 different yoga breathing techniques (Ujjayi, Bhastrika, and Kapalabhati) and normal breathing (control) across all repetitions. After power testing, participants completed an isokinetic test on the Biodex 4 dynamometer using their dominant leg. Subjects had their knee placed at a predetermined starting position (90°) and executed knee extension at 3 randomized testing speeds (60, 180, and 300°·s). The implementation of specific breathing protocols before and during the leg press produced no significant differences in power output. For isokinetic power measured at 60, 180, and 300°·s, there was a significant difference among testing speeds (η = 0.639; p < 0.0001) and a significant sex × speed interaction (η = 0.064; p < 0.0001), where men consistently demonstrated greater isoinertial power, isokinetic power, isokinetic torque, and isokinetic work than women. No other significant differences or interactions were detected. The differences between our study and others, which have concluded that adopting specific breathing techniques can enhance core stability and force production during lifting, may be attributable to the acute nature of the design, the novice participants who had insufficient time to practice the breathing techniques or testing protocols, and the use of tests that isolated specific muscle groups. Nonetheless, the current findings do not support the use of yoga breathing techniques as a method to enhance power output, whether used before or during power performance.

The Test-Retest Reliability of Force Plate-Derived Parameters of the Countermovement Push-Up as a Power Assessment Tool.

Muscular power output of the upper limb is a key aspect of athletic and sporting performance. Maximal power describes the ability to immediately produce power with maximal velocity at the point of release, impact, or takeoff, with research highlighting that the greater an athlete's ability to produce maximal power, the greater the improvement in athletic performance. Despite the importance of upper-limb power for athletic performance, there is presently no gold-standard test for upper-limb force development performance. The aim of this study was to investigate the test-retest reliability of force plate-derived measures of the countermovement push-up in active males. Test-retest design. Controlled laboratory. Physically active college athletes (age 24 [3]y, height 1.79 [0.08] m, body mass 81.7 [9.9]kg). Subjects performed 3 repetitions of maximal effort countermovement push-up trials on Kistler force plates on 2 separate test occasions 7 days apart. Peak force, mean force, flight time, rate of force development, and impulse were analyzed from the force-time curve. No significant differences between the 2 trial occasions were observed for any of the derived performance measures. Intraclass correlation coefficient and within-subject coefficient of variation calculations indicated performance measures to have moderate to very high reliability (intraclass correlation coefficient = .88-.98), coefficient of variation = 5.5%-14.1%). Smallest detectable difference for peak force (7.5%), mean force (8.6%), and rate of force development (11.2%) were small to moderate. Force platform-derived kinetic parameters of countermovement push-up are reliable measurements of power in college-level athletes.

The Effects of Back Squats and Front Squats on Sprint Speed and Vertical Jump within Active Individuals

The back squat (BSQ) is among the most popular resistance training (RT) modalities for the purpose of increasing muscular strength and power output. Front squats (FSQ), while not as popular as the BSQ, are arguably another squat modality that may improve muscular strength/power. PURPOSE: This study compared the effects of performing the BSQ and FSQ on squat strength, sprint speed, and vertical jump (VJ). METHODS: Active individuals both male (n=9, age: 30.6±7.6 yrs, height: 179.1±3.8 cms, mass: 87.8±7.8 kgs) and female (n=16, age: 29.4±6.5 yrs, height: 165.3±5.9 cms, mass: 68.5±10.7 kgs) were separated into two groups via a randomized matched pair design based on initial one repetition maximum (1-RM) squat strength. Both experimental groups employed linear periodization RT protocols differing only in that one group executed the BSQ and the other group performed the FSQ as the lower body exercise. No additional lower body auxiliary movements were performed in the study. The dependent variables (DVs) of VJ, 36.6 meter sprint speed, and 1-RM squat strength were collected prior to and following the 6-week RT period. Dependent t-tests were used to compare the DVs from pre to post RT intervention within experimental groups. Independent t-test were used to compare the gain scores for each of the DVs between experimental groups. RESULTS: The VJ had a significant improvement from pre to post RT for both the BSQ (pre: 52.9±10.1, post: 56.0±10.9 cm) and FSQ (pre: 47.4±10.9, post: 49.9±12.1 cm) groups (p<0.05). The 36.6 m sprint improved significantly from pre to post RT for both the BSQ (pre: 5.9±0.7, post: 5.6±0.5 sec) and FSQ (pre: 6.3±0.7, post: 5.8±0.6 sec) groups (p<0.05). The squat 1-RMs also improved significantly from pre to post RT for both the BSQ (pre: 100.5±34.2, post: 110.3±36.6 kgs) and FSQ (pre: 77.8±31.0, post: 87.5±29.1 kgs) groups (p<0.05). When comparing gain scores between each group there were no significant differences between the BSQ and FSQ groups for any of the DVs (p>0.05). CONCLUSION: Within the parameters of this study, both FSQ and BSQ RT programs improved muscular strength, power and sprint speed in active individuals. Coaches and active individuals may consider the FSQ and BSQ as interchangeable squat modalities providing squat modality variability within RT protocols.

Matching Participants for Triceps Surae Muscle Strength and Tendon Stiffness Does Not Eliminate Age-Related Differences in Mechanical Power Output During Jumping.

Reductions in muscular power output and performance during multi-joint motor tasks with aging have often been associated with muscle weakness. This study aimed to examine if matching younger and middle-aged adults for triceps surae (TS) muscle strength and tendon stiffness eliminates age-related differences in muscular power production during drop jump. The maximal ankle plantar flexion moment and gastrocnemius medialis tendon stiffness of 29 middle-aged (40–67 years) and 26 younger (18–30 years) healthy physically active male adults were assessed during isometric voluntary ankle plantar flexion contractions using simultaneous dynamometry and ultrasonography. The elongation of the tendon during the loading phase was assessed by digitizing the myotendinous junction of the gastrocnemius medialis muscle. Eight younger (23 ± 3 years) and eight middle-aged (54 ± 7 years) adults from the larger subject pool were matched for TS muscle strength and tendon stiffness (plantar flexion moment young: 3.1 ± 0.4 Nm/kg; middle-aged: 3.2 ± 0.5 Nm/kg; tendon stiffness: 553 ± 97 vs. 572 ± 100 N/mm) and then performed series of drop jumps from different box heights (13, 23, 33, and 39 cm) onto a force plate (sampling frequency 1000 Hz). The matched young and middle-aged adults showed similar drop jump heights for all conditions (from lowest to highest box height: 18.0 ± 3.7 vs. 19.7 ± 4.8 cm; 22.6 ± 4.2 vs. 22.9 ± 4.9 cm; 24.8 ± 3.8 vs. 23.5 ± 4.9 cm; 25.2 ± 6.2 vs. 22.7 ± 5.0 cm). However, middle-aged adults showed longer ground contact times (on average 36%), lower vertical ground reaction forces (36%) and hence lower average mechanical power (from lowest to highest box height: 2266 ± 563 vs. 1498 ± 545 W; 3563 ± 774 vs. 2222 ± 320 W; 4360 ± 658 vs. 2475 ± 528 W; 5008 ± 919 vs. 3034 ± 435 W) independent of box height. Further, leg stiffness was lower (48%) in middle-aged compared to younger adults for all jumping conditions and we found significant correlations between average mechanical power and leg stiffness (0.70 ≤ r ≤ 0.83; p < 0.01). Thus, while jumping performance appears to be unaffected when leg extensor muscle strength and tendon stiffness are maintained, the reduced muscular power output during lower limb multi-joint tasks seen with aging may be due to age-related changes in motor task execution strategy rather than due to muscle weakness.

Resistance Training Alters the Proportion of Skeletal Muscle Fibers but Not Brain Neurotrophic Factors in Young Adult Rats.

Antonio-Santos, J, Ferreira, DJS, Gomes Costa, GL, Matos, RJB, Toscano, AE, Manhães-de-Castro, R, and Leandro, CG. Resistance training alters the proportion of skeletal muscle fibers but not brain neurotrophic factors in young adult rats. J Strength Cond Res 30(12): 3531–3538, 2016—Resistance training (RT) is related to improved muscular strength and power output. Different programs of RT for rats have been developed, but peripheral and central response has not been evaluated directly in the same animal. To test the hypothesis that RT induces central and peripheral adaptations, this study evaluated the effects of a RT on the performance of a weekly maximum overload test, fiber-type typology, and brain neurotrophic factors in young adult rats. Thirty-one male Wistar rats (65 ± 5 days) were divided in 2 groups: nontrained (NT, n = 13) and trained (T, n = 18). Trained group was submitted to a program of RT ladder climbing, gradually added mass, 5 days per week during 8 weeks at 80% of individual maximum overload. This test was weekly performed to adjust the individual load throughout the weeks for both groups. After 48 hours from the last session of exercise, soleus and extensor digital longus (EDL) muscles were removed for myofibrillar ATPase staining analysis. Spinal cord, motor cortex, and cerebellum were removed for RT-PCR analysis of BDNF and insulin-like growth factor-1 (IGF-1) gene expression. In EDL muscle, T animals showed an increase in the proportion of type IIb fibers and a reduction of type IIa fibers. Insulin-like growth factor-1 gene expression was reduced in the cerebellum of T animals (NT: 1.025 ± 0.12; T: 0.57 ± 0.11). Our data showed that 8 weeks of RT were enough to increase maximum overload capacity and the proportion of glycolytic muscle fibers, but there were no associations with the expression of growth neurotrophic factors.

Muscular effects of vitamin D in young athletes and non-athletes and in the elderly.

Muscles are major targets of vitamin D. Exposure of skeletal muscles to vitamin D induces the expression of multiple myogenic transcription factors enhancing muscle cell proliferation and differentiation. At the same time vitamin D suppresses the expression of myostatin, a negative regulator of muscle mass. Moreover, vitamin D increases the number of type II or fast twitch muscle cells and in particular that of type IIA cells, while its deficiency causes type IIA cell atrophy. Furthermore, vitamin D supplementation in young males with low vitamin D levels increases the percentage of type IIA fibers in muscles, causing an increase in muscular high power output. Vitamin D levels are strongly associated with exercise performance in athletes and physically active individuals. In the elderly and in adults below the age of 65, several studies have established a close association between vitamin D levels and neuromuscular coordination. The aim of this review is to appraise our current understanding of the significance of vitamin D on muscular performance in both older and frail individuals as well as in younger adults, athletes or non-athletes with regard to both ordinary everyday musculoskeletal tasks and peak athletic performance.

Optimizing post activation potentiation for explosive activities in competitive sports.

Post activation potentiation (PAP) has shown improved performance during movements requiring large muscular power output following contractions under near maximal load conditions. PAP can be described as an acute enhancement of performance or an enhancement of factors determining an explosive sports activity following a preload stimulus. In practice, PAP has been achieved by complex training, which involves a combination of a heavy loaded exercise followed by a biomechanically similar explosive activity, best if specific for a particular sport discipline. The main objective of this study was to investigate the effects of PAP on performance in explosive motor activities specific for basketball, luge and athletics throws. The novel approach to the experiments included individualized recovery time (IRT) between the conditioning exercise and the explosive activity. Additionally, the research groups were homogenous and included only competitive athletes of similar age and training experience. Thirty one well trained athletes from 3 different sport disciplines participated in the study. All athletes performed a heavy loaded conditioning activity (80-130%1RM) followed by a biomechanically similar explosive exercise, during which power (W) or the rate of power development (W/s/kg) was evaluated. The results of our experiment confirmed the effectiveness of PAP with well-trained athlets during explosive motor activities such as jumping, throwing and pushing. Additionally, our research showed that eccentric supramaximal intensities (130% 1RM) can be effective in eliciting PAP in strength trained athletes. Our experiments also showed that the IRT should be individualized because athletes differ in the strength level, training experience and muscle fiber structure. In the three experiments conducted with basketball players, track and field athletes and luge athletes, the optimal IRT equaled 6 min. This justifies the need to individualize the volume and intensity of the CA, and especially the IRT, between the CA and the explosive activity.

HIGH INTENSITY EXERCISE AND FLEXIBILITY OF THE LOWER LIMBS: DOSE-EFFECT STUDY

ABSTRACT Introduction: Sports scientists have been studying the phenomenon involving different types of exercises and their influence on other activities. Stretching exercises have a negative influence on muscular strength and power output, as do high intensity or long duration cardiovascular training. Nevertheless, several studies have found the opposite to be true Nevertheless, few investigations have studied the opposite. Objective: To determine whether high intensity power exercise influences muscular flexibility in an acute manner. Methods: A sample of forty-three male and female young adults aged between 18 and 28 years, with a mean age of 22.88 + 3.04 years, who have practiced physical activity for at least six months. To determine flexibility, the sit-and-reach test was used. For the high intensity training, a 45º leg press was used. A 10-rep movement was performed at 85% of 1 RM, in both pre- and post-tests. Statistic analysis was conducted using the ANOVA and Scheffer's post-hoc tests, with a level of significance for differences of &lt; 0.05. Results: Comparison of the pre- and post-tests proved to be statistically significant from the baseline from the fourth to the seventh repetitions. Conclusion: Strength exercises at 85% of 1RM seem to significantly increase range of motion in an acute manner, and the growth of this range of motion has a dose-effect response.

Optimal Timing for Post-Activation Potentiation in Women Collegiate Volleyball Players.

Post-activation potentiation (PAP) has been shown to acutely amplify muscular power output and may be advantageous for athletes looking to improve performance. PAP may have an acute window of effectiveness between 2 to 20 min. With correct timing and implementation it may be possible to induce PAP in competitive situations. The purpose of this study was to examine the time frame of potentiation following a PAP warm-up in collegiate female volleyball players. In this study, nine female collegiate volleyball players completed three laboratory sessions over the course of 10 days. During the first session, the athlete’s 5-RM back squat was determined for subsequent use as the conditioning activity to initiate PAP. A repeated measures experimental design was then employed for Sessions 2 and 3 where half of the participants alternately performed either a dynamic or PAP warm-up prior to performing a standing long jump (SLJ) at 2, 6, 10, 14, and 18 min. A mixed-factor repeated measures ANOVA was used to determine the effects of the two warm-up strategies (PAP vs. dynamic) on standing long jump (SLJ) performance across time. There was a significant effect for time (p < 0.01) and warm-up strategy (p < 0.01). Bonferroni post hoc techniques determined that the SLJs that followed the PAP warm-up were significantly greater at 2 (4.8%), 6 (3.6%), and 10 (3.6%) min compared to SLJs post-dynamic warm-up (p < 0.05). However, those differences did not persist at 14 or 18 min (p > 0.05). Further analysis included non-parametric pairwise comparisons (Wilcoxon signed-rank tests) between the SLJ scores at 2, 6, 10, 14, and 18 min (PAP vs. dynamic). The non-parametric results were consistent with the parametric results. Within the parameters of this study, it is concluded that performing a 5-RM back squat induces a measureable PAP effect for up to 10 min.

Effects of Circadian Rhythm on Power, Force, and Hormonal Response in Young Men.

Circadian rhythms (CRs) persist in many physiological systems related to performance. The effects of circadian patterns on dynamic muscular power are minimal and conflicting. Furthermore, no study to date has investigated the effect of CR on bench press throws (BPTs) despite its popularity as a modality to increase muscular power. The purpose of this study was to examine the effects of circadian variations on muscular power output and hormonal changes in men. College aged men (n = 7, age: 23.6 ± 1.3 years, height: 179.9 ± 5.4 cm, and body mass: 81.5 ± 19.7 kg.) were recruited for this repeated measures study. Testing occurred at 4 different times of day (04:00, 10:00, 16:00, and 22:00 hours). Testosterone (T) and cortisol (C) hand dynamometer strength (GS), heart rate (HR), mental readiness (MR), BPT and squat jumps (SJs), power (P), and force (F) were measured at each time point. Statistical significance was set at (p ≤ 0.05). There were no significant differences in HR, MR, and GS among all time points. There were no decrements in P or F in BPT or SJ among any time point (p ≥ 0.05). Testosterone and C decreased significantly throughout the day (p ≤ 0.05). Although P and F output differed at various percentages of 1 repetition maximum, they were not affected by circadian pattern, such that muscular performance was not impaired at any time point. Practical implications of these data indicate that high force and power exercises using BPT or SJ may be performed any time of day without detrimental decreases in acute performance.

The Reliability of a Rotational Power Assessment of the Core

Context: Most athletic upper-body power generation involves high levels of neuromuscular activation/coordination of a rotational nature. Therefore, it is important to assess athletic ability that replicates the rotational activity of athletes. However, a paucity of research currently measures rotational power of the core. Objective: Establish inter-day reliability of chop and lift mean power output via a linear position transducer on rotational reliant power athletes. Design: Controlled laboratory study. Setting: Professional cricket training facilities. Population: Eight male professional cricket players (age= 23±3.38 years, height= 186±10.06 cm, mass= 89.71±8.12 kg) with a resistance (>2 years) training background volunteered to participate in the study. Intervention: A linear position transducer was attached to the weight stack of a cable pulley system to determine the peak power outputs associated with a chop and lift movement. Assessment occurred on three occasions separated by at least seven days.Asymmetry, intraclass correlation coefficients (ICCs) and coefficient of variations (CV) were calculated and used to quantify the absolute and relative consistency of the testing procedures. Results: The mean peak power outputs for chop and lift ranged from 404 - 494W and 277-314W respectively, the power outputs differing minimally (2.7-6.3%) between the left and right sides. Coefficients of variation of 7.4% - 19% were reported, with intraclass correlation coefficients of 0.54 - 0.94 observed between testing occasions. Conclusion: Mean muscular power output associated with the lift assessment reported greatest reliability in well trained athletes.The asymmetry between sides was relatively small suggesting balanced multi-planar trunk development in the current throwing athletes. Equipment limitations (load related), training status and variable selection (mean or peak power) need to be considered prior to rotational assessment of the core. It is recommended that the lift movement is utilized in rotational power assessments, or that greater familiarization is undertaken when administering the chop assessment.

The acute effect of lower-body training on average power output measured by loaded half-squat jump exercise

Background: High muscular power output is required in many athletic endeavors in order for success to be achieved. In the scientific community postactivation potentiation and its effect on performance are often discussed. There are many studies where the effect of resistance exercise on motor performance (such as vertical jump performance and running speed) has been investigated but only a few of them studied power output. Objective: The purpose of this study was to determine the acute responses to a 2 set loaded half-squat jumps and 2 set loaded back half-squat protocols designed to induce the acute maximum average power output during loaded half-squat jumps. Methods: A randomized cross-over design was used. 11 participants of this study performed 3 trials in randomized order separated by at least 48 hours where maximum average power output was measured. The specific conditioning activities were comprised of 2 sets and 4 repetitions of half-squat jumps, 2 sets and 4 repetitions of back half-squat exercises and a control protocol without an intervention by specific a conditioning activity. Participants were strength trained athletes with different sport specializations (e.g. ice-hockey, volleyball). Mean age of the athletes was 22 ± 1.8 years, body mass 80 ± 7.1 kg and body height 185 ± 6.5 cm. Analysis of variance with repeated measures was used to determine differences between pre- and post-condition in each protocol, as well as between conditioning protocols, and also effect size was used to evaluate practical significance. Results: Maximum average power was significantly enhanced after application of the half-squat jump condition protocol (1496.2 ± 194.5 to 1552 ± 196.1 W, Δ ~ 3.72%, p < .001) and after application of the back half-squat protocol (1500.7 ± 193.2 to 1556 ± 191.2 W, Δ ~ 3.68%, p < .001) after 10 min of rest. Power output after control protocol was significantly decreased (1516.7 ± 221.8 to 1506.9 ± 231.1 W, Δ ~ 0.64%, p = .02) after 10 min of rest. Conclusions: It appears that using this type of exercise with individualized external load could be a useful method to enhance average power output in training of athletes in a variety of sports with regards to their training background.

The Effects of Heat and Active Stretch on Subjects Performing the Wingate Power Test

Pre-participation static stretching (SS) along with heat application to increase the temperature of the tissues is performed to improve joint range of motion (ROM); presumably by increasing the elasticity of connective tissue during eccentric and concentric muscle actions that are components of dynamic exercise. PURPOSE: To compare the effect of the following conditions ): no static stretching (nSS), heat no static stretch (HnSS), Heat and static stretch (HSS), and static stretch (SS) on indices of the Wingate Power Test (WPT); peak power (PP), mean power (MP), total work (TW), total time to peak power (TTPP). METHODS: 12 male (age 20.2 ± 1.2 yr, ht 181 ± 5.3 cm, wt 73.1 ± 7.9 kg) intercollegiate soccer players were randomly assigned to 4 treatment conditions using a counterbalanced order for nSS, HnSS, HSS, and SS. 7 ROM exercises (plantar/dorsi flexion, Achilles tendon stretch, hamstring/quadriceps stretch, hip abductor, and gluteal stretch) were performed by subjects for a duration of 7 min on dry land or immersed up to the level of the umbilicus in a temperature control (T 43.3 ± 1.6 °C) water bath. WPT was performed within 4 min of condition. A 1-way ANOVA for repeated measures set at the p< .05 level and a post hoc analysis was used to determine contrasting conditions. RESULTS: MP, passive heat (HnSS) or combined with exercise (HSS) were significantly different than the no stretch (nSS) condition (p<.05). TW was significantly lower in the HSS and SS trial compared to the nSS trial. (P< .05) While not statistically significant, the nSS condition compared to all others achieved the lowest TTPP. CONCLUSION: Prior to performance, indices of muscular power and work output are adversely affected by increasing the distensibility of muscle tissue by active ROM exercise and/or passive heat.Table: No title available.

The Effects of Scapular Stabilization Exercise on the Muscular Functions and Pain Release of Shoulder Joints in Youth Baseball Players

We investigated the effect of scapular stabilization exercise on shoulder joints mobilization and pain release in youth baseball players. Total 15 youth baseball players were voluntarily participated, and randomly divided into one of two experimental groups: either stabilization exercise group (EXE, n=7) or control group (NonE, n=8). Stabilization exercises (i.e., punching, scapular retraction, scapular fold, shrug, pull over, seated press, scaption with retraction, body blade, rotator cuff) were administered to EXE (8 weeks, 3 timesᆞwk, 60-100 min·session). Muscular power using Biodex system 3, full range of motion (ROM) with a goniometer, and the degree of pain with the Visual Analogue Scale was assessed at both baseline and the time point of completion of 8 weeks training program. Twoway ANOVA (group vs. time) was adopted to observe any interactive effects between factors. The statistical significance level was set at α=.05. There was an improvement in muscular power at both slow (i.e., 60/sec) and medium (i.e., 180/sec) speed setting in isokinetic instrument during internal and external rotation on dominant shoulder, and internal rotation only (not with external rotation) on non-dominant shoulder. There was no change in ROM in NonE, but total ROM was significantly expanded in EXE, revealing only degree of internal rotation increased. VAS significantly decreased in EXE. In conclusion, scapular stabilization exercise exerted positive effect on muscular power output, full range of motion and pain release on shoulder joint in youth baseball players. This indicates that scapular stabilization exercise possibly exert meaningful effect in injury prevention and sport performance.