Predicting Time to Take-Off in a Countermovement Jump for Maximal Quickness from Upright and Squat Starting Positions.

A countermovement jump (CMJ) is common in sport and often time-constrained. Little is known about contributors to quickness in jumps. This study examined effective predictors of time to take-off and effects of the starting position on reaction time and take-off time in a countermovement jump performed for quickness from upright and squat positions. Forty-nine collegiate athletes performed CMJs for quickness from upright and squatting starting positions to 75% of their maximal jump height. Several variables were calculated from the kinetic data related to jump performance. Correlation and multiple regression were used to determine variables related and predictive of time to take-off under both conditions. Paired t-tests evaluated differences in reaction and take-off times between conditions. In the upright condition, an increasing rate of force development and force, and decreasing time variables, impulses, and countermovement depth were associated with shorter time to take-off. The time to take-off prediction included rates of force development, force, time, and impulse. In the squat condition, shorter time to take-off was associated with lesser time variables, eccentric impulse, force at the end of the eccentric phase, and countermovement depth, and a greater rate of force development, concentric impulse, peak power, peak force, and reaction time. The time to take-off prediction equation included time to the bottom of the countermovement, time to peak force, and peak power. Reaction and take-off times were longer in the upright condition. Quick jump efficiency may be improved by strategies to increase maximum strength and the eccentric rate of force development while decreasing countermovement depth and time to bottom.

Predicting Firefighters' Physical Ability Test Scores from Anaerobic Fitness Parameters & Mental Toughness Levels.

Physical ability test (PAT) evaluates firefighters' (FF) occupational capacity. The contribution of anaerobic systems during PAT and mental toughness (MT) relationship to PAT is unexplored. PAT modeling based on anaerobic fitness (AF), MT, and respective relationships were examined. Fourteen male FFs (Age: 29.0 ± 7.0 years) completed a PAT composed of occupationally-specific tasks in full gear. On a separate day, a series of AF assessments were performed (handgrip-dynamometry: HG; vertical-jump: VJ; Margaria-Kalamen: MK; 300-yard shuttle run: 300YD). MT was evaluated using military training MT inventory (MTMTI) and sports MT questionnaire (SMTQ). We tested the PAT model using multiple backward regression and related correlations coefficients at p < 0.05. A 78% proportion of PAT was explained by AF parameters (F2,13 = 20.2, <0.05). PAT was significantly correlated with HG (r = -0.71, p < 0.01), VJ (r = -0.73, p < 0.01), MK (r = -0.75, p < 0.01), and with 300YD (r = 0.60, p < 0.05). MT did not demonstrate significant correlation with PAT (p > 0.01). Anaerobic system significantly contributes to PAT performance. FFs should optimize AF training, which would allow for enhanced occupational performance in PAT. Further investigation into psychological determinants of FFs is recommended.

Lack of Correlation Between Natural Pelvic Tilt Angle with Hip Range of Motion, and Hip Muscle Torque Ratio.

Excessive anterior and posterior pelvic tilts (PT) angles are associated with overuse injuries of the lower limbs and of the lumbo-pelvic-hip complex. There is a lack of evidence that correlates anterior and posterior PT angles with limited hip internal rotation (IR) and external rotation (ER), and hip muscles torque ratios. The purpose of this study was to examine the correlation between averaged anterior/posterior PT angle in standing position and hip IR and ER range of motion (ROM), hip adductors and abductors (Add/Abd) torque ratio, and hip flexors and extensors (Flexor/Extensor) torque ratio. Twenty-six healthy participants participated in this study, fifteen females (22.0 ± 2.8 yrs, 163.5 ± 7.5 cm, 65.9 ± 10.4 kg) and eleven males (22.0 ± 2.2 yrs, 178.5 ± 4.5 cm, 78.4 ± 8.7 kg). Hip muscle torques were collected with an isokinetic dynamometer, five trials at 30 degrees per second (deg· s-1) and at 60 deg· s-1. The measurement of PT in standing natural position and hip IR and ER ROM in functional weight-bearing lunge position were recorded, using a 3D Motion Analysis System. There were no significant correlations between PT angle and hip IR and ER (p ≥ 0.05), no significant correlations between PT angle and hip Add/Abd torque ratio (p > 0.05), and no significant correlations between PT angle and hip Flexor/Extensor torque ratio (p > 0.05). The measurement of PT angle in standing natural position was not associated with hip IR and ER ROM and hip Add/Abd and Flexor/Extensor torque ratios, in healthy population.

Lower extremity biomechanics and muscle activity differ between 'new' and 'dead' pointe shoes in professional ballet dancers.

The purpose of this study was to compare lower extremity (LE) biomechanics and muscle activity between 'new' and 'dead' pointe shoes in professional female ballet dancers performing relevé and arabesque. We compared sway area, peak ankle moments, and tibialis anterior and medial gastrocnemius muscle activation amplitudes. Nine ballet dancers participated (age = 22.2 ± 2.2 years, height = 163.2 ± 6.3 cm, body mass = 50.8 ± 6.5 kg) executed three trials of relevé and arabesque on pointe shoes under two conditions: 'dead' (108-144 training hours) and 'new' (3-36 training hours). While wearing 'dead' pointe shoes, dancers had significantly higher sway area during both relevé and arabesque (p = 0.017 and 0.028, respectively). Dancers exhibit significantly higher tibialis anterior activation (root mean square, %maximum voluntary contraction) during arabesque while wearing 'dead' pointe shoes (p = 0.043). No significant differences were identified in other dependent variables. The increased sway area and tibialis anterior muscle activity when wearing 'dead' pointe shoes during relevé and arabesque movements demonstrates that using 'dead' shoes is more demanding. Our findings provide quantitative evidence of possible deleterious biomechanical changes when wearing dead pointe shoes that may increase LE injury risk in dancers.

Influence of Fatigue on Change of Direction Performance in Soccer Players.

We investigated the acute fatiguing effects of sprint interval training (SIT) on change of direction performance in male and female soccer players. A T-test was performed once before (PRE) and twice following (POST 1 and POST 2) the completion of four sets of 4 s cycle ergometer sprints protocol. The sprint intervals were separated by 25 s active recovery. POST 1 was performed approximately 25 s following the final cycle sprint and POST 2 began two minutes after completing POST 1. Repeated measures ANOVA and Bonferroni post hoc tests were used to determine any significant differences in the time to complete the T-tests. The average power output drop measured during cycle SIT was 30.7 ± 9%. Time to complete the T-test significantly differed among the three tests (PRE: 10.46 ± .17 s; POST 1: 11.67 ± .33 s; POST 2: 10.96 ± .19 s; F (2, 54) = 6.174, p = .003). Post hoc test revealed an increase in time from PRE to POST 1 (p = .002) but no difference between PRE and POST 2 (p = .473). Nine participants (48%) were unable to complete POST 1 without errors; however, ten (52%) participants recovered enough to perform POST 1 without error. These results show that acute fatigue from SIT impairs change of direction performance, but performance can be recovered within a few minutes of rest. Coaches can combine fatigue inducing drills and change of direction training into same sessions with the right rest interval between the training modes.

The Effect of Foam Rolling of the Hamstrings on Proprioception at the Knee and Hip Joints.

The purpose of this study was to determine the acute effect of hamstring foam rolling on proprioception at the knee and hip joints. Twenty-five participants completed two proprioceptive tests on separate days, in a random order. The joint position matching test used no visual feedback. Participants were verbally guided to a target lunge position, which was maintained for six seconds while right hip and knee angles were recorded. After rest, participants reproduced this position without guidance for six seconds. Three trials were completed at baseline, and zero, 10, and 20 minutes post-intervention. In the force matching test, participants completed three trials with feedback about force output from a graph, and three trials without. They gradually applied knee flexion force against the dynamometer until reaching target force output. This test was also completed at baseline, and zero, 10, and 20 minutes post-intervention. A significant main effect was found for absolute knee position matching error (F(1.97, 47.36), p = 0.004). No significant differences were found between post-intervention values at zero and 10 minutes, zero and 20 minutes, or 10 and 20 minutes for absolute hip position matching error or absolute knee force matching error at zero, 10, or 20 minutes (p > 0.05). Foam rolling improved knee joint position sense for at least 20 minutes post-intervention, and did not decrease hip joint position sense or knee joint force sense. This indicates that foam rolling may be used immediately prior to exercise without the risk of injury due to proprioceptive deficits.

The reliability of side to side measurements of upper extremity activity levels in healthy subjects.

BACKGROUND: In both clinical and occupational settings, ambulatory sensors are becoming common for assessing all day measurements of arm motion. In order for the motion of a healthy, contralateral side to be used as a control for the involved side, the inherent side to side differences in arm usage must be minimal. The goal of the present study was to determine the reliability of side to side measurements of upper extremity activity levels in healthy subjects. METHODS: Thirty two subjects with no upper extremity pathologies were studied. Each subject wore a triaxial accelerometer on both arms for three and a half hours. Motion was assessed using parameters previously reported in the literature. Side to side differences were compared with the intraclass correlation coefficient, standard error of the mean, minimal detectable change scores and a projected sample size analysis. RESULTS: The variables were ranked based on their percentage of minimal detectable change scores and sample sizes needed for paired t-tests. The order of these rankings was found to be identical and the top ranked parameters were activity counts per hour (MDC% = 9.5, n = 5), jerk time (MDC% = 15.8, n = 8) and percent time above 30 degrees (MDC% = 34.7, n = 9). CONCLUSIONS: In general, the mean activity levels during daily activities were very similar between dominant and non-dominant arms. Specifically, activity counts per hour, jerk time, and percent time above 30 degrees were found to be the variables most likely to reveal significant difference or changes in both individuals and groups of subjects. The use of ambulatory measurements of upper extremity activity has very broad uses for occupational assessments, musculoskeletal injuries of the shoulder, elbow, wrist and hand as well as neurological pathologies.

In vivo measurement of humeral elevation angles and exposure using a triaxial accelerometer.

OBJECTIVE: The aim of this study was to measure the capability of a triaxial accelerometer (Virtual Corset) to collect humeral elevation angles and exposure parameters in a simulated occupational environment. BACKGROUND: There is a need for an economical ambulatory device to estimate elevation angles and exposure parameters in occupational groups. METHOD: A magnetic tracking device was used to assess the ability of the Virtual Corset to evaluate humeral elevation angles and identify exposure parameters with in vivo dynamic conditions for 16 female dental hygienists. RESULTS: Significant differences were found for the reaching task with the Virtual Corset, underestimating the means of the average humeral elevation angle by 10 degrees and the means for the range of the humeral elevation by 4 degrees. Furthermore, significant differences were found for the exposure parameters with the Virtual Corset, overestimating the jerk by 4% and underestimating the percentage time above 40 degrees and 60 degrees by 9% and 4%, respectively. However, the Virtual Corset was able to identify similar kinematics patterns and exposure data when compared with a magnetic tracking device. CONCLUSION: The outcomes of the study suggest that the Virtual Corset may be useful for data collection during a dental hygienist workday. Professions that have similar patterns of angular velocity and acceleration and humeral range of elevation as the dental hygienist flossing technique may benefit from the use of the Virtual Corset. APPLICATION: This study provides evidence that the Virtual Corset can be used to reconstruct humeral elevation angles and identify exposure parameters in some tasks of dental hygienists.

Ergonomic evaluation of masons laying concrete masonry units and autoclaved aerated concrete.

Masons working with concrete masonry unit block have high rates of work-related musculoskeletal disorders to the low back and shoulders associated with repetitively lifting and buttering heavy block. A new material, autoclaved aerated concrete, may reduce the risk of shoulder and back injury but, ergonomic evaluation is needed. This study evaluated shoulder exposure parameters, low back stress, and worker perceptions in two groups of journey level masons, one using CMU and the other using AAC block. Results indicate that for the left arm AAC masons spent significantly more time than CMU masons in static (38.2% versus 31.1%, respectively), and less time in slow motions (48.2% versus 52.2%, respectively) and faster motions (13.6% versus 16.7%, respectively) (p<0.05). CMU masons had significantly greater shoulder and low back pain (p=0.009) and they held block significantly longer than AAC masons (p<0.001). Low back compressive forces were high for both materials. Masons handling AAC demonstrated less left upper extremity stress but both materials were estimated to be hazardous to the low back.

Scapular kinematics in constrained and functional upper extremity movements.

STUDY DESIGN: Controlled laboratory study using a single-group, repeated-measures design. OBJECTIVES: To investigate scapular kinematics during both constrained and functional shoulder movements. BACKGROUND: Abnormal scapulothoracic joint motion has been associated with pathologies such as shoulder impingement. Constrained protocols are commonly used in the measurement of shoulder kinematics; however, few studies have measured motion during functional tasks. METHODS: Twenty-five healthy subjects participated in this study. Three-dimensional kinematic data from the scapula and humerus with respect to the thorax were collected with a magnetic tracking system. Functional testing consisted of 6 different tasks representing common activities of daily living. Constrained testing consisted of at least 42 arm elevations in various planes. Two-way analyses of variance with repeated measures were used to compare scapular rotations between constrained and functional movements at the same humeral elevation and plane of elevation angles. Intersubject variability was compared between the overhead tasks and the constrained humeral elevation in the scapular plane by using the coefficient of multiple correlations. RESULTS: Significant differences between constrained trials and functional tasks were found for all scapular rotations. A similar pattern was observed for scapular rotations variability between overhead tasks and constrained arm elevation in the scapular plane. CONCLUSION: Care needs to be taken when comparing and generalizing scapular kinematic data from constrained humeral movements and applying it to functional humeral movements.

Static block jump techniques in volleyball: upright versus squat starting positions.

The difference in maximal jump height between static block jump starting from an upright position (upright BJ) and static block jump starting from a squat position (squat BJ) was determined in 10 division II collegiate women volleyball players. Also determined was the difference in take off time for quick block jump, to a constant point above the net, between upright BJs and squat BJs. An AMTI force plate and a video camera (60 Hz) were used to collect the data. Each subject performed three maximal upright BJs and three maximal squat BJs, and five quick upright BJs and five quick squat BJs, randomly. The highest jump for maximal upright BJs and squat BJs, and the fastest jump for quick upright BJs and squat BJs were recorded. There was a significant difference (p < 0.03) between maximal upright BJs and squat BJs in height jump; maximal upright BJ (33.2 cm) was higher by 1.2 cm. No significant difference (p > 0.5) was found for the fastest take off time (approximately 0.7 s) between quick upright BJs and squat BJs. These results suggest that college women volleyball players can jump higher from the upright, compared with the squat, position. They can take off to the same block position equally quickly from either the upright or squat starting position. These data may suggest that conditioning coaches should identify their players' preferred BJ position and incorporate a specific training program to enhance the players' power. Furthermore, the coaches may need to incorporate more specific squat endurance exercises.