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George J. Salem, Man-Ying Wang and Susan Sigward

In order to obtain joint-specific baseline strength characteristics in older adults, clinicians and researchers must have knowledge regarding the relative stability of the various strength tests (the strength difference between repeated measures) and the number of prebaseline practice sessions required to obtain consistent data. To address these needs, the relative multiple-test stability and reliability associated with lower extremity isokinetic and 1-repetition-maximum (1RM) strength measures were assessed in a sample of older adults (N = 30, 65.2 ± 6.3 years), over 4 weeks (T1-T4). Isokinetic ankle plantar-flexion (30°/s) strength and 1RM ankle plantar-flexion, leg-press, and knee-flexion strength exhibited poor stability between Weeks T1 and T2 but stabilized between Weeks T2 and T3 and Weeks T3 and T4. The measures exhibited low incidence of injury and induced low levels of residual muscle soreness. Findings suggest that the 1RM measures require at least 1 prebaseline training session in order to establish consistent baseline performance and are more reliable than isokinetic ankle plantar-flexion tests.

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Rodrigo Antunes Lima, Lisbeth Runge Larsen, Anna Bugge and Lars Bo Andersen

Purpose: The current investigation aimed to investigate the longitudinal association between physical fitness and academic performance over 3 years in adolescents. A secondary aim was to determine to what extent waist circumference mediated the association between physical fitness and academic performance. Methods: For the current study, 1020 students from first grade [mean age: 7.87 (0.34) y] to fifth grade [mean age: 11.87 (0.37) y] were monitored annually for 3 years (2010–2013). Physical fitness was assessed using the Andersen test, 5 × 5-m shuttle run, jump height, and grip strength tests and by constructing a composite score combining all 4 fitness tests. Academic performance was assessed by national standardized tests in Danish language and math. Generalized structural equation modeling was used to evaluate the relationships between these variables. Results: The Andersen test (standardized β = 0.15 SD), shuttle run (β = −0.18 SD), jump height (β = 0.10 SD), and the fitness composite score (β = 0.23 SD) were positively associated with academic performance over 3 years. In addition, waist circumference partially mediated the association between physical fitness and academic performance. Conclusion: Thus, physical fitness abilities should be stimulated during childhood and early adolescence because of their positive association with academic performance.

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Robert van Cingel, Gertjan Kleinrensink, Rob Stoeckart, Geert Aufdemkampe, Rob de Bie and Harm Kuipers

Objective:

To determine concentric shoulder external-internal rotator strength, dominant and non-dominant shoulder differences and agonist/antagonist ratios.

Design:

A transversal study of isokinetic dynamometry of healthy shoulders, 95% confidence intervals are presented.

Participants:

35 asymptomatic elite, male volleyball players.

Measurements:

Peak torque normalized for body weight was recorded at 60, 180, and 300°/sec. with a Cybex 6000 dynamometer.

Results:

(1) internal rotators were significantly stronger than external rotators of the same shoulder; (2) internal rotators of the dominant arm were significantly stronger than of the non-dominant arm; (3) no difference existed between external rotators of the dominant and the non-dominant arm; (4) external–internal rotator ratios of the dominant arm were significantly lower than of the non-dominant arm; and (5) no differences were found between the ratios of each arm separately.

Conclusions:

Data presented are important for interpreting isokinetic shoulder rotator strength tests in elite volleyball players and could be relevant in rehabilitation and prevention of shoulder injuries.

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Irineu Loturco, Lucas A. Pereira, Ciro Winckler, Weverton L. Santos, Ronaldo Kobal and Michael McGuigan

Purpose: To examine the relationships between different loading intensities and movement velocities in the bench-press exercise (BP) in Paralympic powerlifters. Methods: A total of 17 national Paralympic powerlifters performed maximum dynamic strength tests to determine their BP 1-repetition maximum (1RM) in a Smith-machine device. A linear position transducer was used to measure movement velocity over a comprehensive range of loads. Linear-regression analysis was performed to establish the relationships between the different bar velocities and the distinct percentages of 1RM. Results: Overall, the correlations between bar velocities and %1RM were strong over the entire range of loads (R 2 .80–.91), but the precision of the predictive equations (expressed as mean differences [%] between actual and predicted 1RM values) were higher at heavier loading intensities (∼20% for loads ≤70% 1RM and ∼5% for loads ≥70% 1RM). In addition, it seems that these very strong athletes (eg, 1RM relative in the BP = 2.22 [0.36] kg·kg−1, for male participants) perform BP 1RM assessments at lower velocities than those previously reported in the literature. Conclusions: The load–velocity relationship was strong and consistent in Paralympic powerlifters, especially at higher loads (≥70% 1RM). Therefore, Paralympic coaches can use the predictive equations and the reference values provided here to determine and monitor the BP loading intensity in national Paralympic powerlifters.

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Stefan C. Garcia, Jeffrey J. Dueweke and Christopher L. Mendias

Context: Manual isometric muscle testing is a common clinical technique used to assess muscle strength. To provide the most accurate data for the test, the muscle being assessed should be at a length in which it produces maximum force. However, there is tremendous variability in the recommended positions and joint angles used to conduct these tests, with few apparent objective data used to position the joint such that muscle-force production is greatest. Objective: To use validated anatomically and biomechanically based musculoskeletal models to identify the optimal joint positions in which to perform manual isometric testing. Design: In silico analysis. Main outcome measure: The joint position which produces maximum muscle force for 49 major limb and trunk muscles. Results: The optimal joint position for performing a manual isometric test was determined. Conclusion: Using objective anatomical models that take into account the force-length properties of muscles, the authors identified joint positions in which net muscle-force production was predicted to be maximal. This data can help health care providers to better assess muscle function when manual isometric strength tests are performed.

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Kristian M. O’Connor, Carl Johnson and Lauren C. Benson

The function of the hamstrings in protecting the ACL is not fully understood. The purpose of this study was to determine how landing knee mechanics were affected by hamstrings fatigue, analyzed with principal components analysis (PCA). Knee joint mechanics were collected during single-leg stride landings that were followed by lateral and vertical jumps. An isokinetic fatigue protocol was employed to reduce hamstrings strength by 75% at the cessation of the exercise protocol. On the landing test day, participants performed the stride landing maneuvers before and after the fatigue protocol. PCA was performed on the landing knee joint angle, moment, and power waveforms, and MANOVAs were conducted on the retained PCs of each waveform (P < .05). On the strength test day, hamstrings strength recovery was assessed with an identical fatigue protocol followed by strength assessment ~75 s after the cessation of exercise. Pre- and postexercise hamstrings strength on this day was assessed with a dependent t test (P < .05). The hamstrings strength remained significantly reduced by ~8% postexercise (75 s). For stride landings followed by vertical jumps, there were significantly reduced knee flexion angles, extensor moments, and energy absorption. This was indicative of a stiffer landing strategy postfatigue, which has been associated with increased ACL loading.

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Christopher A. Bailey, Kimitake Sato, Angus Burnett and Michael H. Stone

The purpose of this investigation was to determine the existence of bilateral strength and force-production asymmetry and evaluate possible differences based on sex, as well as strength level. Asymmetry was assessed during weight-distribution (WtD) testing, unloaded and lightly loaded static- (SJ) and countermovement-jump (CMJ) testing, and isometric midthigh-pull (IMTP) strength testing. Subjects included 63 athletes (31 male, 32 female) for WtD, SJ, and CMJ tests, while 129 athletes (64 male, 65 female) participated in IMTP testing. Independent-samples t tests were used to determine possible differences in asymmetry magnitude between males and females, as well as between strong and weak athletes. Cohen d effect-size (ES) estimates were also used to estimate difference magnitudes. Statistically different asymmetry levels with moderate to strong ESs were seen between males and females in WtD, 0-kg SJ (peak force [PF]), 20-kg SJ (peak power [PP]), 0-kg CMJ (PF, PP, net impulse), and 20-kg CMJ (PF), but no statistical differences were observed in IMTP variables. Dividing the sample into strong and weak groups produced statistically significant differences with strong ES estimates in IMTP PF and rate of force development, and many ESs in jump symmetry variables increased. The results of this investigation indicate that females may be more prone to producing forces asymmetrically than males during WtD and jumping tasks. Similarly, weaker athletes displayed more asymmetry than stronger athletes. This may indicate that absolute strength may play a larger role in influencing asymmetry magnitude than sex.

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Taina Rantanen, Pertti Era, Markku Kauppinen and Eino Heikkinen

This study analyzes the associations of socioeconomic status (SES), health, and physical activity with maximal isometric strength in 75-year-old men (n = 104) and women (n = 191). Maximal isometric strength was measured with dynamometers; the forces were adjusted using body weight. The maximal forces for women varied from 66% (trunk flexion) to 73% (knee extension) of those of the men. SES was not associated with muscle force. For men the trunk forces and elbow flexion force correlated negatively with the number of chronic diseases, index of musculoskeletal pain, and self-rated health. For women all the strength test results correlated with self-rated health; the other health indicators showed significant correlation with trunk extension force only. For both sexes the physically more active exhibited greater strength. The index of musculoskeletal symptoms explained the variance on trunk force factor in both sexes. It was concluded that a higher level of everyday physical activity and good values in the state-of-health indicators were the most important variables explaining greater strength among the elderly.

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Gregory M. Gutierrez, Catherine Conte and Kristian Lightbourne

Head impacts are common in contact sports, but only recently has there been a rising awareness of the effects of subconcussive impacts in adolescent athletes. A better understanding of how to attenuate head impacts is needed and therefore, this study investigated the relationship between neck strength, impact, and neurocognitive function in an acute bout of soccer heading in a sample of female high school varsity soccer players. Seventeen participants completed the ImPACT neurocognitive test and had their isometric neck strength tested (flexion, extension, and bilateral flexion) before heading drills. Each participant was outfitted with custom headgear with timing switches and a three-dimensional accelerometer affixed to the back of the head, which allowed for measurement of impact during heading. Participants performed a series of 15 directional headers, including 5 forward, 5 left and 5 right headers in a random order, then completed the ImPACT test again. Neurocognitive tests revealed no significant changes following heading. However, there were statistically significant, moderate, negative correlations (r = −0.500:−0.757, p < .05) between neck strength and resultant header acceleration, indicating that those with weaker necks sustained greater impacts. This suggests neck strengthening may be an important component of any head injury prevention/reduction program.

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Michael P. Corcoran, Miriam E. Nelson, Jennifer M. Sacheck, Kieran F. Reid, Dylan Kirn, Roger A. Fielding, Kenneth K.H. Chui and Sara C. Folta

This cluster-randomized trial was designed to determine the efficacy of a 6-month exercise-nutritional supplement program (ENP) on physical function and nutritional status for older adults and the feasibility of implementing this program in a senior living setting. Twenty senior-living facilities were randomized to either a 3 day per week group-based ENP led by a trained facility staff member or a health education program (SAP). Participants (N = 121) completed a short physical performance battery, 400-m walk, handgrip strength test, and mini-nutrition assessment. 25-hydroxyvitamin D [25(OH)D], insulin-like growth-factor 1 (IGF-1), and activity level were also measured. The ENP did not significantly improve physical function or nutritional status compared with the SAP. Compared with baseline, participants in the ENP engaged in 39 min less physical activity per week at 6 months. Several facility characteristics hindered implementation of the ENP. This study highlights the complexity of implementing an evidence-based program in a field setting.