Peak Isometric Force Research Articles

A Single Bout of On-Ice Training Leads to Increased Interlimb Asymmetry in Competitive Youth Hockey Athletes.

Interlimb asymmetry (ILA) refers to an anatomical or physiological imbalance between contralateral limbs, which can influence neuromuscular function. Investigating the influence of neuromuscular fatigue on ILA may be critical for optimizing training programs, injury rehabilitation, and sport-specific performance. The purpose of this study was to determine if a single bout of ice hockey-specific exercise creates or exacerbates lower-limb ILA. Before and after an on-ice training session, 33 youth ice-hockey athletes (14.9 [1.7]y; 11 females) performed 3 repetitions of a maximal vertical countermovement jump (CMJ), an eccentric hamstring contraction, and maximal isometric hip adduction and abduction contractions. Force- and power-related variables were analyzed to determine limb-specific neuromuscular function. The on-ice session reduced maximal isometric hip adduction (left: 7.3% [10.3%]; right: 9.5% [9.6%]) and abduction (left: 4.9% [6.9%]; right: 5.0% [8.1%]) force, but did not impair (P ≥ .10) CMJ performance (jump height, relative peak power, braking duration, and total duration). After the on-ice session, ILA was greater for CMJ propulsive impulse (6.3% [2.9%] vs 5.1% [2.6%]), CMJ braking rate of force development (19.3% [7.6%] vs 15.2% [6.4%]), and peak isometric hip adduction force (6.7% [5.5%] vs 6.1% [4.1%]). In conclusion, hockey-specific exercise leads to increased ILA for multiple force-related metrics, which may be a compensatory mechanism to maintain bilateral task performance when fatigued.

Phenomenological Muscle Constitutive Model With Actin-Titin Binding for Simulating Active Stretching.

The force produced by a muscle depends on its contractile history, yet human movement simulations typically employ muscle models that define the force-length relationship from measurements of fiber force during isometric contractions. In these muscle models, the total force-length curve can have a negative slope at fiber lengths greater than the fiber length at which peak isometric force is produced. This region of negative stiffness can cause numerical instability in simulations. Experiments have found that the steady-state force in a muscle fiber following active stretching is greater than the force produced during a purely isometric contraction. This behavior is called residual force enhancement. We present a constitutive model that exhibits force enhancement, implemented as a hyperelastic material in the febio finite element software. There is no consensus on the mechanisms responsible for force enhancement; we adopt the assumption that the passive fiber force depends on the sarcomere length at the instant that the muscle is activated above a threshold. We demonstrate the numerical stability of our model using an eigenvalue analysis and by simulating a muscle whose fibers are of different lengths. We then use a three-dimensional muscle geometry to verify the effect of force enhancement on the development of stress and the distribution of fiber lengths. Our proposed muscle material model is one of the few models available that exhibits force enhancement and is suitable for simulations of active lengthening. We provide our implementation in febio so that others can reproduce and extend our results.

A Specific Test of Starting Blocks: Intrasession and Intersession Reliability of Isometric Strength Using a Functional Electromechanical Dynamometer

Aims: To determine the intrasession and intersession reliability of the isometric force at three different starting block positions, to compare the intrasession and intersession reliability of the peak and average isometric force of three different starting block positions, and to compare the intrasession and intersession reliability of three different starting block positions. Methods: Eighteen male college students participated in this study. A repeated measures design was used to evaluate the intrasession and intersession reliability of isometric force in three different starting block positions. Results: Very high and extremely high reliability of the average and peak isometric force of the three positions of the starting blocks were obtained, with ICC ranging from 0.63 to 0.91 and a CV close to 10%. Peak force was able to determine the outcomes of the bilateral position with higher reliability than the mean force, and the dominant was the most reliable position for assessing the starting blocks. Conclusion: The functional electromechanical dynamometer can be used with a high level of reliability to assess the force exerted in the starting blocks.

The Autoregulation Rest-Redistribution Training Method Mitigates Sex Differences in Neuromuscular and Perceived Fatigue During Resistance Training.

To examine the sex differences in performance and perceived fatigue during resistance training prescribed using traditional (TRA) and autoregulation rest-redistribution training (ARRT) approaches. Twelve resistance-trained men and 12 women completed 2 sessions including the bench-press exercise matched for load (75% of 1-repetition maximum), volume (24 repetitions), and total rest (240s). Sessions were performed in a counterbalanced randomized design with TRA consisting of 3 sets of 8 repetitions with 120-second interset rest and ARRT employing a personalized combination of clusters, repetitions per cluster, and between-clusters rest regulated with a 20% velocity-loss threshold. The effects of TRA and ARRT on velocity loss, unilateral isometric peak force, and rating of fatigue (ROF) were compared between sexes. The velocity loss was generally lower during ARRT compared with TRA (-0.47% [0.11%]), with velocity loss being mitigated by ARRT to a greater extent among males compared with females (-0.37% [0.15%]). A smaller unilateral isometric peak force decline was observed after ARRT than TRA among males compared with females (-38.4 [8.4]N). Lower ROF after ARRT than TRA was found among males compared to females (-1.97 [0.55]AU). Additionally, males reported greater ROF than females across both conditions (1.92 [0.53]AU), and ARRT resulted in lower ROF than TRA overall (-0.83 [0.39]AU). The ARRT approach resulted in decreased velocity loss, peak force impairment, and ROF compared with TRA in both sexes. However, male subjects exhibited more pronounced acute within-session benefits from the ARRT method.

Full Hill-type muscle model of the I1/I3 retractor muscle complex in Aplysia californica.

The coordination of complex behavior requires knowledge of both neural dynamics and the mechanics of the periphery. The feeding system of Aplysia californica is an excellent model for investigating questions in soft body systems' neuromechanics because of its experimental tractability. Prior work has attempted to elucidate the mechanical properties of the periphery by using a Hill-type muscle model to characterize the force generation capabilities of the key protractor muscle responsible for moving Aplysia's grasper anteriorly, the I2 muscle. However, the I1/I3 muscle, which is the main driver of retractions of Aplysia's grasper, has not been characterized. Because of the importance of the musculature's properties in generating functional behavior, understanding the properties of muscles like the I1/I3 complex may help to create more realistic simulations of the feeding behavior of Aplysia, which can aid in greater understanding of the neuromechanics of soft-bodied systems. To bridge this gap, in this work, the I1/I3 muscle complex was characterized using force-frequency, length-tension, and force-velocity experiments and showed that a Hill-type model can accurately predict its force-generation properties. Furthermore, the muscle's peak isometric force and stiffness were found to exceed those of the I2 muscle, and these results were analyzed in the context of prior studies on the I1/I3 complex's kinematics in vivo.

Force-Time Characteristics in Collegiate Weightlifters Using Two Isometric Pull Protocols

The isometric mid-thigh pull (IMTP) is commonly used to measure isometric strength of characteristics of weightlifters. The isometric pull from the start position (IPSP) has not been studied as much as the IMTP but may potentially be a viable option for a weightlifting monitoring program. This study aims to compare isometric force-time characteristics from both the IMTP and IPSP to weightlifting competition performance. Collegiate weightlifters’ performances were compared to isometric peak force (IPF), rate of force development (RFD), and allometrically scaled peak force (IPFa) of both isometric testing protocols by a Pearson’s Correlation Coefficient. Strong correlations between weightlifting performance and force-time characteristics for both protocols were found with IPSP having slightly higher correlations. This suggests that both isometric testing protocols are viable tools for predicting weightlifting performance. It may be useful to include both protocols in a weightlifting monitoring program.

TRIM Enhances Angiogenesis in Dystrophic Muscle 140 Days Post Treatment

Background: Duchenne Muscular Dystrophy (DMD) causes limb muscle dysfunction and impaired mobility while promoting ischemia in effected muscles. For treatment, we developed a novel biomaterial, Time Release Ion Matrix (TRIM), that promotes angiogenesis and enhances muscle structure and function in dystrophic (D2. mdx) mice at 14- and 70-days post injection (dpi). Whether TRIM remains effective at 140 dpi is unknown. Hypothesis: At 140 dpi in D2. mdx mice TRIM will: 1) enhance isometric force and myofiber cross-sectional area (CSA) of the tibialis anterior (TA) muscle; and 2) stimulate angiogenic growth factors and increase vascularity. Methods: The right and left TA of adult male D2. mdx mice (male, n=7-8, age 7 months) were injected with saline alone (control) or 250 μg of TRIM suspended in saline. At 140 dpi, the left TA muscle was isolated for in situ muscle force measurements and histological analysis; the right TA was frozen for biochemical analysis. Muscle cross-sections were immunostained for laminin (myofiber borders), DAPI (nuclei), and CD31 (endothelial cells). Vascular endothelial growth factor (VEGF) ELISA and immunoblots were performed on muscle homogenates. Results: No difference in peak isometric force was recorded between groups at 140 dpi (means ± SE: TRIM, 65.4 ± 2.7g; Saline, 62.7 ± 1.5g; P= 0.34). TRIM enhanced the relative frequency of myofibers >1000 μm2 by 27% vs. saline (TRIM, 56 ± 2%; Saline, 44 ± 3%; P= 0.006). DAPI staining revealed a 36% increase in central nuclei indicating myofiber regeneration (TRIM, 30.0 ± 1.7%; Saline, 22.0% ± 2.5; P=0.02). Microvessel area (CD31 staining, μm2) was 2.5-fold greater in treated TA’s (TRIM, 131 ± 12 μm2; Saline, 53 ± 6 μm2, P=0.0001). In muscle homogenates, TRIM had no effect on [VEGF] (TRIM, 102 ± 5%; Saline, 100 ± 4%; P= 0.79), while STAT3 activation was greater (TRIM, 129 ± 11%; Saline, 100 ± 7%; P= 0.04). Conclusion: At 140 days following injection of TRIM into the TA muscle of dystrophic mice, peak isometric force was unchanged while myofiber CSA was enhanced. Furthermore, TRIM promotes angiogenic growth factors and muscle vascularity, which should promote the ability to sustain physical activity. University of Missouri Coulter Biomedical Accelerator (SSS), American Physiological Society SURF (AGN), Texas A&M Department of Kinesiology and Sport Management (ABM). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Compatibility of eugenol anesthesia with classroom physiology experiments on nerve and muscle of frogs

Frogs serve as valuable model organisms for studying physiological responses of nerve, skeletal muscle and the heart in undergraduate biology labs. Heretofore, induced hypothermia has been the preferred technique for pain and stress reduction prior to euthanasia by pithing. However, AVMA guidelines discourage hypothermia for restraint or euthanasia of amphibians and advocate anesthetic overdose as preferable to pithing alone. Unfortunately, the primary anesthetic used in fish and other aquatic invertebrates, MS-222, blocks normal nerve and muscle function in leopard frogs and renders them useless for classroom physiology experiments, as demonstrated by Medler (2019). Eugenol is a safe and affordable anesthetic that is effective in amphibians. We sought to test the hypothesis that eugenol anesthesia is compatible with classroom nerve and muscle experiments on frogs. Bullfrogs and leopard frogs were immersed in a bath of eugenol suspended in tap water at 275 to 350 mg/L. At various time points, a four step reflex test was performed including tests of righting response, superficial pain reflex, deep pain reflex, and corneal blink reflex. Once all reflexes were absent, the frog was euthanized by pithing and the gastrocnemius muscle was prepared for force recordings. The sciatic nerve was stimulated with a bipolar stimulating electrode while gastrocnemius force was measured using an isometric force transducer. The threshold voltage eliciting a muscle contraction and the peak isometric twitch force were recorded at 15 minute intervals for 2 hours. Control frogs were sedated by immersion in ice water for 20 to 30 minutes, pithed when reflexes were substantially weakened, and then subjected to the same stimulation protocol and force measurements. At these doses, eugenol reliably induces loss of reflexes in 20 to 35 minutes and neuromuscular preparations maintain the ability to respond to electrical stimulation. Preliminary results suggest that eugenol may produce a modest elevation of threshold voltage and a modest reduction in maximum twitch force compared to control frogs euthanized without chemical anesthesia. Eugenol may be an effective anesthetic to prepare bullfrogs and leopard frogs for classroom experiments on nerve and muscle. Funding was provided by the Bill and Linda Frost Fund. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

TRIM Enhances Dystrophic Muscle Function 70 Days Post Treatment

Background: Duchenne Muscular Dystrophy (DMD) is associated with limb muscle dysfunction caused by progressive weakness and degeneration of skeletal muscle. Current FDA-approved therapeutic strategies are less effective than originally hoped. Our alternative approach was to develop a novel biomaterial, Time Release Ion Matrix (TRIM), shown to release angiogenic ions and enhance muscle structure and function at 14 days post injection (dpi) in dystrophic (D2. mdx) mice. However, the long-term effects of TRIM are unknown. Hypothesis: At 70 days post injection in D2. mdx mice TRIM will: 1) enhance isometric force and myofiber cross-sectional area (CSA) of the tibialis anterior (TA) muscle; and 2) promote vascular endothelial growth factor (VEGF) availability and muscle vascularity. Methods: The right and left TA of adult male D2. mdx mice (n=6-7, age 5 months) were injected with saline alone (control) or 250 μg of TRIM suspended in saline. At 70 dpi, the left TA was isolated for in situ muscle force measurements and histological analysis; the right TA was frozen for biochemical analysis. Muscle cross-sections were immunostained for laminin (myofiber borders), DAPI (nuclei), and CD31 (endothelial cells). An ELISA for VEGF was performed on homogenates of frozen muscles. Results: TA’s injected with TRIM increased peak isometric force (means ± SE: TRIM 70.9 ± 1.8 g; Saline, 65.9 ± 1.1 g; P= 0.04). TRIM-treated TA’s had a 2.2-fold increase in relative frequency of myofibers >1000 μm2 (TRIM, 31.8 ± 3.7%; Saline, 14.4 ± 1.9%; P= 0.001), and reduced the frequency of myofibers <400 μm2 by 32% (TRIM, 38.6% ± 2.8; Saline, 56.5% ± 3.5; P= 0.001). DAPI staining revealed a 50% increase in central myonuclei indicative of regenerated myofibers (TRIM, 30.2 ± 1.7%; Saline, 20.2 ± 1.3%; P=0.0006). Microvessel area (CD31 staining; μm2) was 2.1-fold greater in treated TA’s (TRIM, 135.6 ± 8.7 μm2; Saline, 63.6 ± 4.5 μm2; P=0.0001). In muscle homogenates, TRIM increased [VEGF] (TRIM, 139 ± 10%; Saline, 100 ± 6%; P= 0.009) Conclusion: Results support the hypothesis that 70 days following injection of TRIM into the TA of dystrophic mice, muscle force and myofiber CSA are enhanced. Moreover, TRIM enhances VEGF with increased vascularity, suggesting that the angiogenic effects of TRIM complement those on myogenesis and contractile function towards restoring muscle structure and function in DMD. University of Missouri Coulter Biomedical Accelerator (SSS), Texas A&M Department of Kinesiology and Sport Management (ABM). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

New hand dynamometer activforce isometric muscle activation on single joint muscle force of volleyball players

Isometric muscle activation of single joint to volleyball players is critic on sport performance to produce potential muscle force, however isometric measurement limited in isokinetic muscle activity measurement of volleyball players. Indeed, hand dynamometers commonly use in various body isometric force. Professional volleyball players age 16.23 ± 0.59 yr, body mass 60.22 ± 4.64 kg, hight 1.69 ± 0.04 m participated to peak and average isometric force measurement over 8 week pre and post test. Accordingly, single joint muscle force production measurement of volleyball players tested on isometric muscle activation using a new hand dynamometer activforce 2. Isometric muscle activation tests consisted of 24 body region from upper and lower compartment. For this isometric muscle action test detected on peak force outcomes (SEM: 37.90; CV: 1.79) and average force outcomes (SEM: 33.62; CV: 1.84). The high isometric muscle action joint loading performing mechanical test application recommended on athletic population to using isometric potential high contraction model by strength training performance separately in-season and off-season measurement modeling. Conclusion, peak and average force production progressive isometric modeling of volleyball athletes worked to current sport–health condition. As out, conclusion must be advanced isometric force measurement proper work in sport-specific tasks. The proper isometric force must be repeat sport performance outcome in different sport modalities.

The Relationship Between Isometric Midthigh Pull Force-Time Characteristics and 2-km Load-Carrying Performance in Trained British Army Soldiers.

Nevin, JP, Bowling, K, Cousens, C, Bambrough, R, and Ramsdale, M. The relationship between isometric midthigh pull force-time characteristics and 2-km load-carrying performance in trained British army soldiers. J Strength Cond Res 38(2): 360-366, 2024-Load carriage is a fundamental military occupational task. As such, the aim of this study was to assess the relationship between isometric force-time characteristics and loaded march performance. Furthermore, this study aimed to investigate the relationship between isometric force-time characteristics and standing long jump (SLJ) performance. Thirty-nine, full-trained, male British Army infantry soldiers (age 31 ± 6.1 years; height 176 ± 7.3 cm; body mass 85.8 ± 11.5 kg) performed three isometric midthigh pull trials, three SLJ trials, and a 2-km loaded march carrying an external load of 25 kg. Both the isometric midthigh pull test (intraclass correlation coefficient [ICC] 0.965) and SLJ (ICC 0.916) demonstrated excellent reliability. Relationships between all variables were assessed using Pearson's correlation coefficient. Isometric peak force (r = -0.059), relative peak force (r = -0.135), and rate of force development (r = -0.162) displayed a small correlation with loaded march time to completion. However, isometric relative peak force displayed a large relationship with SLJ performance (r = 0.545; p = <0.01). Our data demonstrate that isometric lower-limb strength measures account for <2% of the total variance observed in 2-km loaded march performance. As such, the use of isometric lower-limb force-time characteristics as a proxy measure of load-carrying ability should be questioned. However, relative isometric strength seems to demonstrate a significant relationship with SLJ performance. As such, isometric testing may have utility in regard to assessing explosive strength, monitoring neuromuscular fatigue, and assessing training readiness in military populations.

Changes in isometric mid-thigh pull peak force and symmetry across anterior cruciate ligament reconstruction rehabilitation phases.

Whether functionally relevant strength assessments, such as the isometric mid-thigh pull (IMTP), can be used either bilaterally or unilaterally to evaluate and guide rehabilitation progress in those with anterior cruciate ligament reconstruction (ACLR) is under-researched. This study assessed changes in peak force (PF) and asymmetry across 3 phases for bilateral and unilateral IMTP assessments in patients with ACLR. Peak isometric force from the IMTP was compared to peak torque from isokinetic dynamometry as well as against a cohort of healthy, uninjured individuals. Participants (ACLR, n = 15) completed bilateral and unilateral IMTP assessments at weeks 12 (baseline), 16 (phase 3), and 20 (phase 4) of rehabilitation to evaluate changes in PF and asymmetry. Asymmetry was evaluated using the asymmetry angle. Isometric data from the IMTP were compared to that from an isokinetic dynamometer as well as against a cohort of healthy, uninjured participants (n = 63) allowing for a detailed analysis of limb-specific force production. The PF during the bilateral IMTP increased for both the injured (0.94 N/kg) and uninjured (0.26 N/kg) limbs from baseline to phase 4, whereas the PF of the injured limb increased by 1.5 N/kg during the unilateral IMTP in the same time frame. Asymmetry values systematically reduced by ∼1% and ∼0.5% for the bilateral and unilateral IMTP tests from baseline to phase 4. Significant differences in PF of the injured limb were evident between those with ACLR and healthy controls across all phases (p = 0.022-0.001). The rate of progression in PF capacity was dependent on test type, amounting to 0.1 and 0.2 body weights per week for the bilateral and unilateral IMTP respectively. Small-to-large correlations (r = 0.12-0.88) were evident between IMTP PF and peak torque from the isokinetic dynamometer as well as between asymmetry metrics from both tests. The findings suggest that IMTP PF has potential for monitoring changes in PF and asymmetry during the ACLR rehabilitation progress. Both injured limb and uninjured limb show improvement in force-generating capacity, implying a positive adaptation to rehabilitation protocols. The findings highlight that ACLR is a unilateral injury that requires bilateral rehabilitation.

The Effects of Low-Load Squat Jump and Maximal Isometric Priming Exercise on Muscular Performance and Perceptual State.

Harrison, PW, James, LP, Jenkins, DG, McGuigan, MR, Holmberg, PM, and Kelly, VG. The effects of low-load squat jump and maximal isometric priming exercise on muscular performance and perceptual state. J Strength Cond Res 38(1): 1-9, 2024-The aim of this study was to examine responses at 3 and 27 hours after low-load jump squat (LL) and maximal isometric half-squat (ISO) priming stimuli. Fifteen resistance-trained males performed LL (4 × 3 at 20% 1 repetition maximum [1RM]), ISO (4 × 3 seconds), and control (CON) activities (standardized warm-up) in a randomized and counterbalanced order. Countermovement jump (CMJ) and isometric midthigh pull tests were conducted to assess performance changes after priming and CON activities. No clear changes in CMJ measures were found after priming activities compared with CON. However, small effect size improvements were found after priming stimuli completed on the same day. A 2.9% decrease in concentric phase duration (CI = 0.3-5.9, p = 0.333, Cliff's delta = -0.156) and a 9.1% increase in RSImod (CI = 0.2-12.3, p = 0.151, Cliff's delta = -0.218) occurred at 3 hours after LL compared with CON. Braking phase duration (CI = 0.8-10.6, p = 0.333, Cliff's delta = -0.213) was 2.9% shorter at 3 hours after ISO compared with CON. No clear changes in isometric peak force occurred after priming activities compared with CON. Additionally, questionnaires were completed to assess perceptual state and perceived effectiveness of the priming stimulus to influence performance. An increase in the "effect of activity" was perceived at 3 hours after LL and ISO (p = 0.013-0.044, Cliff's delta = 0.578-0.6) and at 27 hours after ISO (p = 0.99, Cliff's delta = 0.173) compared with CON. An increase in "muscular heaviness" was also reported at 3 hours after ISO compared with CON (p = 0.199, Cliff's delta = 0.320). The collective findings suggest limited benefits over the day after LL and ISO priming stimuli. However, as there was substantial variation in individual responses, the relative nature of priming responses should be considered when prescribing similar strategies in practical environments.

Test-Retest Reliability of 3 Specific Strength Tests in Professional Handball Players.

Current devices to assess strength performance in handball may not be sufficiently sports-specific and reliable methods. Functional electromechanical dynamometry is a new technology that allows the development of accurate strength tests in athletes. To determine the absolute and relative reliability and to compare the reliability of the right and left side, and mean and peak force of 3 specific strength tests in handball players with a functional electromechanical dynamometer: unilateral pullover, standing lift, and step forward. Fourteen male handball players of the first Spanish division (28.79 [4.81]y; 10.38 [4.63]y of professional experience) performed a repeated-measurement design. Three testing sessions were performed (one per week). The first measurement consisted of 4 isometric tests (right and left unilateral pullover, and right and left standing lift) to obtain isometric peak force, and in the second and third sessions, 6 incremental tests until failure (right and left unilateral pullover, and right and left standing lift, right and left step forward) were performed. The tests provided high reliability or acceptable reliability for mean and peak strength of unilateral pullover, standing lift and step forward (intraclass correlation coefficient = .83-.97; coefficient of variation = 3.90-11.57). Effect side was negligible in any of the parameters, except for a small effect side in the left peak force for unilateral pullover and a small effect side on the left side for a step forward. Significant differences in reliability (coefficient of variation ratio > 1.15) were found between the right and left sides and peak and mean force in all exercises except peak force in unilateral pullover and step forward. These results confirm that the tests could be applied to assess physical performance in handball at the same time as regular gym training. Moreover, this is an excellent opportunity to individualize the player's weekly load.

Countermovement Jump and Isometric Strength Test–Retest Reliability in English Premier League Academy Football Players

Purpose: To examine the test–retest reliability of countermovement jump (CMJ) and isometric strength testing measures in elite-level under-18 and under-23 academy football players. Methods: A total of 36 players performed 3 maximal CMJs and isometric abductor (IABS), adductor (IADS), and posterior chain (IPCS) strength tests on 2 separate test days using dual force plates (CMJ and IPCS) and a portable strength testing device (IABS and IADS). Relative (intraclass correlation coefficient) and absolute (coefficient of variation, standard error of the measurement, and minimal detectable change [MDC%]) reliabilities for 34 CMJ, 10 IABS, 10 IADS, and 11 IPCS measures were analyzed using between-sessions best, mean, and within-session methods. Results: For all methods, relative reliability was good to excellent for all CMJ and all IADS measures and poor to good for all IABS and IPCS measures. Absolute reliability was good (ie, coefficient of variation &lt; 10%) for 27 (best) and 28 (mean) CMJ variables and for 6 (IABS and IADS) and 2 (IPCS) isometric measures. Commonly used CMJ measures (jump height, eccentric duration, and flight-time:contraction-time ratio) had good to excellent relative reliability and an MDC% range of 14.6% to 23.7%. Likewise, commonly used isometric peak force measures for IABS, IADS, and IPCS had good to excellent relative reliability and an MDC% range of 22.2% to 26.4%. Conclusions: Commonly used CMJ and isometric strength measures had good test–retest reliability but might be limited by their MDC%. Rate-of-force-development measures (for all isometric tests) and impulse measures (IPCS) are limited by poor relative and absolute reliability and high MDC%. MDC% statistics should be considered in the context of typical responsiveness.

The Relationship Between Lower-Body Force-Time Variables and Skating Performance in Female Ice Hockey Players.

Ice hockey is a team invasion sport characterized by repeated high-intensity skating efforts, technical and tactical skill, physical contact, and collisions requiring considerable levels of muscular strength. The purpose of this study was to evaluate the relationships between lower-body vertical force-time metrics and skating qualities in subelite female ice hockey players. A cross-sectional cohort design was employed utilizing 14 athletes (body mass = 66.7 [1.8]kg; height = 171.6 [6.2]cm; age = 21.1 [1.7]y). The relationships between metrics of lower-body strength collected from a drop jump, squat jump, countermovement jump, loaded countermovement jump, and an isometric squat and 4 skating qualities collected from a linear sprint, repeated sprint test, and a multistage aerobic test were evaluated. The regression models revealed a positive relationship between relative peak force in the isometric squat and skating multistage aerobic test performance (r2 = .388; P = .017) and a positive relationship between repeated-sprint ability and eccentric mean force during the loaded countermovement jump (r2 = .595; P = .001). No significant relationships were observed between strength metrics and skating acceleration or maximal velocity. These data suggest that skating ability is most affected by relative isometric strength in female ice hockey players. It is recommended that practitioners focus training on tasks that improve relative force output. It is also recommended that isometric relative peak force be used as a monitoring metric for this cohort.

Reliability of a handball specific strength test battery and the association with sprint and throwing performance in young handball players.

A greater motivation for coaches to be more involved in assessment could be the development of specific strength tests closer to specific handball tasks. Therefore, the aims were to determine the reliability of a handball specific strength test battery in young handball players using a functional electromechanical dynamometer (FEMD) and to evaluate the association between the strength test battery and performance measurements. Thirty-two young handball players (25% males and 75% females) performed a repeated-measurement design over four weeks. The players conducted one session per week, with each measurement consisting of two isometric tests to obtain isometric peak force, and four incremental tests. Moreover, performance handball tests (sprint and throwing velocity [TV]) were recorded. The reliability of the whole handball specific strength tests was very high for the peak and mean strength (ICC=0.70-0.85; CV=8.49-13.99; SEM=0.44-0.67 kg). The step forward had a moderate association with 5 to 10 meters' time. The highest correlation between TV<inf>mean</inf> was found with the peak strength of standing lift and between TV<inf>peak</inf> with peak strength of unilateral throw. The sprint total time could be explained by Body Mass Index and peak strength of the standing lift in the 40% and the TV<inf>peak</inf> could be explained by arm span and mean strength of the standing lift in the 68%. The high reliability for all exercises and the significant correlation with handball performance (sprint time and TV) allow us to include these tests in handball team evaluation and training.

Stuart has got the PoWeR! Skeletal muscle adaptations to a novel heavy progressive weighted wheel running exercise model in C57BL/6 mice.

Murine exercise models are developed to study the molecular and cellular mechanisms regulating muscle mass. A progressive weighted wheel running model, named 'PoWeR', was previously developed to serve as a more translatable alternative to involuntary resistance-type exercise models in rodents, such as synergist ablation. However, mice still run great distances despite the added resistance as evidenced by a large glycolytic-to-oxidative shift in muscle fibre type. Thus, PoWeR reflects a blended resistance/endurance model. In an attempt to bias PoWeR further towards resistance-type exercise, we developed a novel heavy PoWeR model (hPoWeR) utilizing higher wheel loads (max of 12.5g vs 6g). Adult male C57BL/6 mice voluntarily performed an 8-week progressive loading protocol (PoWeR or hPoWeR). Running distance peaked at ∼5-6kmday-1 in both treatments and was maintained by PoWeR mice, but declined in the hPoWeR mice as load increased beyond 7.5g. Peak isometric force of the gastrocnemius-soleus-plantaris complex tended to increase in wheel running treatments. Soleus mass increased by 19% and 24% in PoWeR and hPoWeR treatments, respectively, and plantaris fibre cross-sectional area was greater in hPoWeR, compared to PoWeR. There were fewer glycolytic and more oxidative fibres in the soleus and plantaris muscles in the PoWeR treatment, but not hPoWeR. Collectively, these data suggest hPoWeR may modestly alter skeletal muscle supporting the aim of better reflecting typical resistance training adaptations, in line with decreased running volume and exposure to higher resistance. Regardless, PoWeR remains an effective hypertrophic concurrent training model in mice.

Examining the Link between Isokinetic Strength Metrics and Ball Speed in Women’s Soccer

The shot performance of female soccer players is one of the most critical factors in winning a soccer match. It is essential to thoroughly clarify the kinetic factors that can improve shot performance. This study explores the connections between ball velocity post-shooting and isokinetic knee extension (EXT) and flexion (FLX) strength performances among female soccer players. Thirteen voluntary players from professional leagues took part in the research study. The study analyzed the average and peak concentric (Con) and eccentric (Ecc) torques, isometric (Iso) strength performances at angular velocities of 60°/s, 180°/s and 300°/s, the time required to reach peak torque, and ball velocities during shooting. The relationships among these variables were investigated separately for the dominant (D) and non-dominant (ND) legs. The analysis unveiled significant correlations between ball velocities and D-EXT (Absolute) peak torque at an angular velocity of 60°/s (r = 0.597; p &lt; 0.05), D-%IPS (r = −0.580; p &lt; 0.05), and ND-FLX (Absolute) average torque (r = 0.559; p &lt; 0.05). Moreover, notable associations were observed between ball velocities and ND-EXT (Absolute) (r = 0.581; p &lt; 0.05), as well as ND-FLX (Absolute) (r = 0.602; p &lt; 0.05) average torques at an angular velocity of 180°/s. Additionally, significant relationships were found between ball velocities and peak (r = 0.664; p = 0.013) and average (r = 0.660; p = 0.014) torques generated during ND-EXT (Absolute) at an angular velocity of 300°/s. However, the connections between the time to reach peak torque, eccentric and isometric forces, and ball velocities were not statistically significant (p &gt; 0.05). The results of the study indicate that enhancing concentric isokinetic strength development at 60°/s, 180°/s, and 300°/s angular velocities, along with balanced strengthening of the ND extremity, holds paramount importance in elevating shot performance among female soccer players, particularly in the context of rapid shot strategies.

Individuals with rotator cuff tears unsuccessfully treated with exercise therapy have less inferiorly oriented net muscle forces during scapular plane abduction

Exercise therapy for individuals with rotator cuff tears fails in approximately 25.0 % of cases. One reason for failure of exercise therapy may be the inability to strengthen and balance the muscle forces crossing the glenohumeral joint that act to center the humeral head on the glenoid. The objective of the current study was to compare the magnitude and orientation of the net muscle force pre- and post-exercise therapy between subjects successfully and unsuccessfully (e.g. eventually underwent surgery) treated with a 12-week individualized exercise therapy program. Twelve computational musculoskeletal models (n = 6 successful, n = 6 unsuccessful) were developed in OpenSim (v4.0) that incorporated subject specific tear characteristics, muscle peak isometric force, in-vivo kinematics and bony morphology. The models were driven with experimental kinematics and the magnitude and orientation of the net muscle force was determined during scapular plane abduction at pre- and post-exercise therapy timepoints. Subjects unsuccessfully treated had less inferiorly oriented net muscle forces pre- and post-exercise therapy compared to subjects successfully treated (p = 0.039 & 0.045, respectively). No differences were observed in the magnitude of the net muscle force (p > 0.05). The current study developed novel computational musculoskeletal models with subject specific inputs capable of distinguishing between subjects successfully and unsuccessfully treated with exercise therapy. A less inferiorly oriented net muscle force in subjects unsuccessfully treated may increase the risk of superior migration leading to impingement. Adjustments to exercise therapy programs may be warranted to avoid surgery in subjects at risk of unsuccessful treatment.