The reliability of linear position transducer, force plate and combined measurement of explosive power-time variables during a loaded jump squat in elite athletes

The purpose of this study was to determine the between day reliability of power-time measures calculated with data collected using the linear position transducer or the force plate independently, or a combination of the two technologies. Twenty-five male rugby union players performed three jump squats on two occasions one week apart. Ground reaction forces were measured via a force plate and position data were collected using a linear position transducer. From these data, a number of power-time variables were calculated for each method. The force plate, linear position transducer and a combined method were all found to be a reliable means of measuring peak power (ICC = 0.87-0.95, CV = 3.4%-8.0%). The absolute consistency of power-time measures varied between methods (CV = 8.0%-53.4%). Relative consistency of power-time measures was generally comparable between methods and measures, and for many variables was at an acceptable level (ICC = 0.77-0.94). Although a number of time-dependent power variables can be reliably calculated from data acquired from the three methods investigated, the reliability of a number of these measures is below that which is acceptable for use in research and for practical applications.     

Reliability and magnitude of mechanical variables assessed from unconstrained and constrained loaded countermovement jumps

This study aimed to (1) assess the reliability of the force, velocity, and power output variables measured by a force plate and a linear velocity transducer (LVT) for both the unconstrained and constrained loaded countermovement jump (CMJ), and (2) examine the effect of both the CMJ type and the measurement method on the magnitudes of the same variables. Twenty-three men were tested on the free CMJ and the CMJ constrained by a Smith machine. Maximum values of force, velocity, and power were recorded by a force plate and by a LVT attached to a bar loaded by 17, 30, 45, 60, and 75 kg. The reliability of all mechanical variables proved to be high (ICC > 0.70; CV < 10%) and similar for two CMJ types. However, force plate-derived measures displayed greater reliability than the LVT. The LVT also markedly overestimated the magnitudes of the mechanical variables, particularly at lower external loads. Therefore, although both jump types and both methods could be acceptable for routine testing, we recommend the force platform due to a higher reliability and more accurate magnitudes of the obtained variables. The unconstrained loaded CMJ could also be recommended due to the simpler equipment needed.     

The reliability of isoinertial force–velocity–power profiling and maximal strength assessment in youth

The purpose of this study was to quantify the inter-session reliability of force–velocity–power profiling and estimated maximal strength in youth. Thirty-six males (11–15 years old) performed a ballistic supine leg press test at five randomized loads (80%, 100%, 120%, 140%, and 160% body mass) on three separate occasions. Peak and mean force, power, velocity, and peak displacement were collected with a linear position transducer attached to the weight stack. Mean values at each load were used to calculate different regression lines and estimate maximal strength, force, velocity, and power. All variables were found reliable (change in the mean [CIM] = ? 1 to 14%; coefficient of variation [CV] = 3–18%; intraclass correlation coefficient [ICC] = 0.74–0.99), but were likely to benefit from a familiarization, apart from the unreliable maximal force/velocity ratio (CIM = 0–3%; CV = 23–25%; ICC = 0.35–0.54) and load at maximal power (CIM = ? 1 to 2%; CV = 10–13%; ICC = 0.26–0.61). Isoinertial force–velocity–power profiling and maximal strength in youth can be assessed after a familiarization session. Such profiling may provide valuable insight into neuromuscular capabilities during growth and maturation and may be used to monitor specific training adaptations.     

Reliability of force-velocity relationships during deadlift high pull

This study aimed to evaluate the within- and between-session reliability of force, velocity and power performances and to assess the force-velocity relationship during the deadlift high pull (DHP). Nine participants performed two identical sessions of DHP with loads ranging from 30 to 70% of body mass. The force was measured by a force plate under the participants’ feet. The velocity of the ‘body + lifted mass’ system was calculated by integrating the acceleration and the power was calculated as the product of force and velocity. The force-velocity relationships were obtained from linear regression of both mean and peak values of force and velocity. The within- and between-session reliability was evaluated by using coefficients of variation (CV) and intraclass correlation coefficients (ICC). Results showed that DHP force-velocity relationships were significantly linear (R² > 0.90, p < 0.05). Within sessions and between sessions, mean and peak forces during DHP showed a strong agreement (CV < 3%, ICC > 0.94), mean and peak velocities showed a good agreement (CV < 9%, 0.78 < ICC < 0.92). It was concluded that DHP performance and its force-velocity relationships are highly reliable and can therefore be utilised as a tool to characterise individuals’ muscular profiles.     

Reliability of a commercially available and algorithm-based kinetic analysis software compared to manual-based software

There is a need for reliable analysis techniques for kinetic data for coaches and sport scientists who employ athlete monitoring practices. The purpose of the study was: (1) to determine intra- and inter-rater reliability within a manual-based kinetic analysis program; and (2) to determine test-retest reliability of an algorithm-based kinetic analysis program. Five independent raters used a manual analysis program to analyse 100 isometric mid-thigh pull (IMTP) trials obtained from previously collected data. Each trial was analysed three times. The same IMTP trials were analysed using an algorithm-based analysis software. Variables measured were peak force, rate of force development from 0 to 50 ms (RFD50) and RFD from 0 to 200 ms (RFD200). Intraclass correlation coefficients (ICC) and coefficient of variation (CV) were used to assess intra- and inter-rater reliability. Nearly perfect reliability was observed for the manual-based (ICC > 0.92). However, poor intra- and inter-rater CV was observed for RFD (CV > 16.25% and CV > 32.27%, respectively). The algorithm-based method resulted in perfect reliability in all measurements (ICC = 1.0, CV = 0%). While manual methods of kinetic analysis may provide sufficient reliability, the perfect reliability observed within the algorithm-based method in the current study suggest it is a superior method for use in athlete monitoring programs.     

The validity and reliability of the GymAware linear position transducer for measuring counter-movement jump performance in female athletes

The current study aimed to assess the validity and test–retest reliability of a linear position transducer when compared to a force plate through a counter-movement jump in female participants. Twenty-seven female recreational athletes (19 ± 2 years) performed three counter-movement jumps simultaneously using the linear position transducer and force plate for validity. In addition, 11 elite female athletes (23 ± 6 years) performed 3 counter-movement jumps with the linear position transducer on three separate days for test–retest reliability. Pearson correlations for jump height between the devices were at a high level (r = .90), with the linear position transducer overestimating jump height by 7.0 ± 2.8 cm. The reliability measured by the linear position transducer resulted in a mean intraclass correlation of .70 for jump height, .90 for peak velocity, and .91 for mean velocity. The linear position transducer was reliable for measuring counter-movement jumps in elite female athletes; however, caution should be taken for one-off jump measures as it may over-estimate jump height.     

Leg soft tissue position and velocity data from skin markers can be obtained with good to acceptable reliability following heel impacts

Quantifying soft tissue motion following impact is important in human motion analysis as soft tissues attenuate potentially injurious forces resulting from activities such as running and jumping. This study determined the reliability of leg soft tissue position and velocity following heel impacts. A grid of black dots was applied to the skin of the right leg and foot (n = 20). Dots were automatically detected (ProAnalyst^®) from high-speed records of pendulum and drop impacts. Three trained measurers selected columns of dots on each participant for analysis; one measurer 6 months later. Between- and within-measurer differences in kinematic variables were all relatively small (<0.8 cm for position; <3.7 cm/s for velocity) between-measurers and (<0.5 cm for position; <2.6 cm/s for velocity) within-measurer. Good (coefficients of variation (CV) ≤ 10%) to acceptable (CV > 10% and ≤20%) reliability was shown for 95% of the position measures, with mean CVs of 10% and 11% within-measurers and between-measures, respectively. Velocity measures were less reliable; 40% of the measures showed good to marginal (CV > 20% and ≤30%) reliability. This study established that leg soft tissue position data from skin markers could be obtained with good to acceptable reliability following heel impacts. Velocity data were less reliable but still acceptable in many cases.     

Reliability of force per unit cross-sectional area measurements of the first dorsal interosseus muscle

The purpose of this study was to determine the reliability of maximum voluntary isometric force (MVIF), cross-sectional area (CSA) and force per unit CSA measures, of the first dorsal interosseus (FDI) muscle, using a custom-built dynamometer and ultrasonography. Twenty-seven participants completed MVIF and CSA measurements on two separate occasions under the same conditions. Reliability was determined using paired samples t-tests, systematic bias ratio and ratio limits of agreement (RLoA), intra-class correlation (ICC) and coefficient of variation (CV). MVIF of the FDI muscle (mean ± s; 31.8 ± 7.6 N and 31.6 ± 7.3 N) was not different between trials (P = 0.63); RLoA between trials were 1.00 ×/÷ 1.09, ICC = 0.990 and CV = 3.22%. CSA of the FDI muscle (22.6 ± 6.9 and 22.9 ± 6.9 mm²) was also not different between trials (P = 0.31); RLoA between trials were 0.98 ×/÷ 1.19, ICC = 0.979 and CV = 6.61%. Force per unit CSA was not different between trials (1.49 ± 0.43 and 1.46 ± 0.44 N·mm²; P = 0.18), RLoA were 1.02 ×/÷ 1.17, ICC = 0.985 and CV = 5.76%. The techniques used to determine MVIF and CSA of the FDI muscle were reliable and can be combined to calculate force per unit CSA.     

Reliability and validity of the Zebris FDM-THQ instrumented treadmill during running trials

Little is known about the reliability, validity and smallest detectable differences of selected kinetic and temporal variables recorded by the Zebris FDM-THQ instrumented treadmill especially during running. Twenty male participants (age = 31.9 years (±5.6), height = 1.81 m (±0.08), mass = 80.2 kg (±9.5), body mass index = 24.53 kg/m² (±2.53)) walked (5 km/h) and ran (10 and 15 km/h) on an instrumented treadmill, wearing running shoes fitted with Pedar-X insoles. A test-double retest protocol was conducted over two consecutive days. Maximal vertical force (F_max), contact time (CT) and flight time (FT) data from 10 consecutive steps were collected. Within- and between-day reliability, smallest detectable differences (SDD) and validity (95% limits of agreement (LOA)) were calculated. ICC values for the Zebris for Fmax were acceptable (ICC ≥ 0.7) while CT and FT reliability indices were predominantly good (ICC ≥ 0.8) to excellent (ICC ≥ 0.9). The Zebris significantly underestimated Fmax when compared with the Pedar-X. The 95% LOA increased with speed. SDD ranged between 96 N and 169 N for Fmax, 0.017s and 0.055s for CT and 0.021s and 0.026s for FT. In conclusion, Zebris reliability was acceptable to excellent for the variables examined, but inferior in comparison with Pedar-X. With increased running speeds, a bias effect (underestimation) existed for the Zebris compared with Pedar-X.     

Reliability and variability of day-to-day vault training measures in artistic gymnastics

Inter-day training reliability and variability in artistic gymnastics vaulting was determined using a customised infra-red timing gate and contact mat timing system. Thirteen Australian high performance gymnasts (eight males and five females) aged 11–23 years were assessed during two consecutive days of normal training. Each gymnast completed a number of vault repetitions per daily session. Inter-day variability of vault run-up velocities (at ‐18 to ‐12 m, ‐12 to ‐6 m, ‐6 to ‐2 m, and ‐2 to 0 m from the nearest edge of the beat board), and board contact, pre-flight, and table contact times were determined using mixed modelling statistics to account for random (within-subject variability) and fixed effects (gender, number of subjects, number of trials). The difference in the mean (M_diff) and Cohen's effect sizes for reliability assessment and intra-class correlation coefficients, and the coefficient of variation percentage (CV%) were calculated for variability assessment. Approach velocity (‐18 to ‐2 m, CV = 2.4–7.8%) and board contact time (CV = 3.5%) were less variable measures when accounting for day-to-day performance differences, than pre-flight time (CV = 17.7%) and table contact time (CV = 20.5%). While pre-flight and table contact times are relevant training measures, approach velocity and board contact time are more reliable when quantifying vaulting performance.     

Comparison of the force-, velocity-, and power-time curves recorded with a force plate and a linear velocity transducer

This study aimed to correlate, compare, and determine the reliability of force, velocity, and power values collected with a force plate (FP) and a linear transducer during loaded jumps. Twenty-three swimmers performed an incremental loading test at 25, 50, 75, and 100% of their own body weight on a FP. A linear velocity transducer (LVT) was attached to the bar to assess the peak and the mean values of force, velocity, and power. Both the peak variables (r = 0.94 – 0.99 for peak force, r = 0.83 – 0.91 for peak velocity, and r = 0.90–0.94 for peak power; p < 0.001) and the mean variables (r = 0.96–0.99 for mean force, r = 0.87–0.89 for mean velocity, and r = 0.93–0.96 for mean power; p < 0.001) were strongly correlated between both measurement tools. Differences in the shape of the force-, velocity-, and power-time curves were observed. The LVT data showed a steeper increase in these variables at the beginning of the movement, while the FP recorded larger values in the latter part. Peak values were more reliable than mean values. These results suggest that the LVT is a valid tool for the assessment of loaded squat jump.     

A new approach to determining net impulse and identification of its characteristics in countermovement jumping: reliability and validity

Examining a countermovement jump (CMJ) force-time curve related to net impulse might be useful in monitoring athletes' performance. This study aimed to investigate the reliability of alternative net impulse calculation and net impulse characteristics (height, width, rate of force development, shape factor, and proportion) and validate against the traditional calculation in the CMJ. Twelve participants performed the CMJ in two sessions (48 hours apart) for test–retest reliability. Twenty participants were involved for the validity assessment. Results indicated intra-class correlation coefficient (ICC) of ≥ 0.89 and coefficient of variation (CV) of ≤ 5.1% for all of the variables except for rate of force development (ICC = 0.78 and CV = 22.3%). The relationship between the criterion and alternative calculations was r = 1.00. While the difference between them was statistically significant (245.96 ± 63.83 vs. 247.14 ± 64.08 N s, p < 0.0001), the effect size was trivial and deemed practically minimal (d = 0.02). In conclusion, variability of rate of force development will pose a greater challenge in detecting performance changes. Also, the alternative calculation can be used practically in place of the traditional calculation to identify net impulse characteristics and monitor and study athletes' performance in greater depth.     

Reliability and concurrent validity of a motor skill competence test among 4- to 12-year old children

The purpose of this study was to examine the test-retest reliability, internal consistency and concurrent validity of the Athletic Skills Track (AST). During a regular PE lesson, 930 4- to 12-year old children (448 girls, 482 boys) completed two motor skill competence tests: (1) the Körperkoordination-Test für Kinder (KTK) and (2) an age-related version of the AST (age 4–6 years: AST-1, age 6–9 years: AST-2, and age 9–12 years: AST-3). The test-retest reliability of the AST was high (AST-1: ICC = 0.881 (95% CI: 0.780–0.934); AST-2: ICC = 0.802 (95% CI: 0.717–0.858); and AST-3: ICC = 0.800 (95% CI: 0.669–0.871). The internal consistency, concerning the three age-bands of the AST was above the acceptable level of Cronbach’s α > 0.70 (AST-1: α = 0.764; AST-2: α = 0.700; and AST-3: α = 0.763). There was a moderate to high correlation between the time to complete the AST, and the age- and gender-related motor quotients of the KTK (AST-1: r = ?0.747, p = 0.01; AST-2: r = ?0.646, p = 0.01; and AST-3: r = ?0.602, p = 0.01). The Athletic Skills Track is a reliable and valid assessment tool to assess motor skill competence among 4- to 12-year old children in the PE setting.     

Reliability and validity of different methods of estimating the one-repetition maximum during the free-weight prone bench pull exercise

ABSTRACT

This study examined the reliability and validity of three methods of estimating the one-repetition maximum (1RM) during the free-weight prone bench pull exercise. Twenty-six men (22 rowers and four weightlifters) performed an incremental loading test until reaching their 1RM, followed by a set of repetitions-to-failure. Eighteen participants were re-tested to conduct the reliability analysis. The 1RM was estimated through the lifts-to-failure equations proposed by Lombardi and O’Connor, general load-velocity (L-V) relationships proposed by Sánchez-Medina and Loturco and the individual L-V relationships modelled using four (multiple-point method) or only two loads (two-point method). The direct method provided the highest reliability (coefficient of variation [CV] = 2.45% and intraclass correlation coefficient [ICC] = 0.97), followed by the Lombardi’s equation (CV = 3.44% and ICC = 0.94), and no meaningful differences were observed between the remaining methods (CV range = 4.95–6.89% and ICC range = 0.81–0.91). The lifts-to-failure equations overestimated the 1RM (3.43–4.08%), the general L-V relationship proposed by Sánchez-Medina underestimated the 1RM (?3.77%), and no significant differences were observed for the remaining prediction methods (?0.40–0.86%). The individual L-V relationship could be recommended as the most accurate method for predicting the 1RM during the free-weight prone bench pull exercise.     

Concurrent validity and test–retest reliability of a global positioning system (GPS) and timing gates to assess sprint performance variables

Abstract

There has been no previous investigation of the concurrent validity and reliability of the current 5 Hz global positioning system (GPS) to assess sprinting speed or the reliability of integrated GPS–accelerometer technology. In the present study, we wished to determine: (1) the concurrent validity and reliability of a GPS and timing gates to measure sprinting speed or distance, and (2) the reliability of proper accelerations recorded via GPS–accelerometer integration. Nineteen elite youth rugby league players performed two over-ground sprints and were simultaneously assessed using GPS and timing gates. The GPS measurements systematically underestimated both distance and timing gate speed. The GPS measurements were reliable for all variables of distance and speed (coefficient of variation [CV] = 1.62% to 2.3%), particularly peak speed (95% limits of agreement [LOA] = 0.00 ± 0.8 km · h^?1; CV = 0.78%). Timing gates were more reliable (CV = 1% to 1.54%) than equivalent GPS measurements. Accelerometer measurements were least reliable (CV = 4.69% to 5.16%), particularly for the frequency of proper accelerations (95% LOA = 1.00 ± 5.43; CV = 14.12%). Timing gates and GPS were found to reliably assess speed and distance, although the validity of the GPS remains questionable. The error found in accelerometer measurements indicates the limits of this device for detecting changes in performance.     

Concurrent validity and reliability of torso-worn inertial measurement unit for jump power and height estimation

The purpose of the present study was to evaluate the concurrent validity and test-retest repeatability of torso-worn IMU-derived power and jump height in a counter-movement jump test. Twenty-seven healthy recreationally active males (age, 21.9 [SD 2.0] y, height, 1.76 [0.7] m, mass, 73.7 [10.3] kg) wore an IMU and completed three counter-movement jumps a week apart. A force platform and a 3D motion analysis system were used to concurrently measure the jumps and subsequently derive power and jump height (based on take-off velocity and flight time). The IMU significantly overestimated power (mean difference = 7.3 W/kg; P < 0.001) compared to force-platform-derived power but good correspondence between methods was observed (Intra-class correlation coefficient [ICC] = 0.69). IMU-derived power exhibited good reliability (ICC = 0.67). Velocity-derived jump heights exhibited poorer concurrent validity (ICC = 0.72 to 0.78) and repeatability (ICC = 0.68) than flight-time-derived jump heights, which exhibited excellent validity (ICC = 0.93 to 0.96) and reliability (ICC = 0.91). Since jump height and power are closely related, and flight-time-derived jump height exhibits excellent concurrent validity and reliability, flight-time-derived jump height could provide a more desirable measure compared to power when assessing athletic performance in a counter-movement jump with IMUs.     

Reliability and validity of field-based measures of leg stiffness and reactive strength index in youths

Abstract

The aim of the study was to assess the reliability of a mobile contact mat in measuring a range of stretch–shortening cycle parameters in young adolescents. Additionally, vertical leg stiffness using contact mat data was validated against a criterion method using force–time data. The reliability study involved 18 youths completing a habituation and three separate test sessions, while 20 youths completed a single test session for the validity study. Participants completed three trials of a squat jump, countermovement jump, and maximal hopping test and a single trial of repeated sub-maximal hopping at 2.0 Hz and 2.5 Hz. All tests were performed on the contact mat. Reliability statistics included repeated-measures analysis of variance, intraclass correlation coefficient, and coefficient of variation (CV), while the correlation coefficient (r) and typical error of estimate (TEE) were reported for the validity study. Squat jump height was the most reliable measure (CV = 8.64%), while leg stiffness during sub-maximal hopping, and reactive strength index produced moderate reliability (CV = 10.17–13.93% and 13.98% respectively). Measures of leg stiffness obtained from contact mat data during sub-maximal hopping were in agreement with the criterion measure (r = 0.92–0.95; TEE = 6.5–7.5%), but not during maximal hopping (r = 0.59; TEE = 41.9%). The contact mat was deemed a valid tool for measuring stretch–shortening cycle ability in sub-maximal but not maximal hopping. Although reliability of performance was generally moderate, the tests offer a replicable assessment method for use with paediatric populations.     

Reliability and Validity of Finger Strength and Endurance Measurements in Rock Climbing

Purpose: An advanced system for the assessment of climbing-specific performance was developed and used to: (a) investigate the effect of arm fixation (AF) on construct validity evidence and reliability of climbing-specific finger-strength measurement; (b) assess reliability of finger-strength and endurance measurements; and (c) evaluate the relationship between finger flexor all-out test scores and climbing ability. Methods: To determine the effect of AF, 22 male climbers performed 2 maximal strength and all-out tests with AF (shoulder and elbow flexed at 90°) and without AF (shoulder flexed at 180° and elbow fully extended). To determine reliability, 9 male climbers completed 2 maximal strength tests with and without AF and an all-out and intermittent test without AF. Results: The maximal strength test without AF more strongly determined climbing ability than the test with AF (r² = .48 and r² = .42 for sport climbing; r² = .66 and r² = .42 for bouldering, respectively). Force and time variables were highly reliable; the rate of force development and fatigue index had moderate and low reliability. The maximal strength test with AF provided slightly higher reliability than without AF (intraclass correlation coefficient [ICC] = 0.94, ICC = 0.88, respectively). However, smaller maximal forces were achieved during AF (484 ± 112 N) than without AF (546 ± 132 N). All-out test average force had sufficiently high reliability (ICC = 0.92) and a relationship to sport climbing (r² = .42) and bouldering ability (r² = .58). Conclusion: Finger strength and endurance measurements provided sufficient construct validity evidence and high reliability for time and force parameters. Arm fixation provides more reliable results; however, the position without AF is recommended as it is more related to climbing ability.     

The validity and reliability of a novel app for the measurement of change of direction performance

ABSTRACT

The aim of the present investigation was to analyze the validity and reliability of a novel iPhone app (CODTimer) for the measurement of total time and interlimb asymmetry in the 5 + 5 change of direction test (COD). To do so, twenty physically active adolescent athletes (age = 13.85 ± 1.34 years) performed six repetitions in the COD test while being measured with a pair of timing gates and CODTimer. A total of 120 COD times measured both with the timing gates and the app were then compared for validity and reliability purposes. There was an almost perfect correlation between the timing gates and the CODTimer app for the measurement of total time (r = 0.964; 95% Confidence interval (CI) = 0.95–1.00; Standard error of the estimate = 0.03 s.; p < 0.001). Moreover, non-significant, trivial differences were observed between devices for the measurement of total time and interlimb asymmetry (Effect size < 0.2, p > 0.05). Similar levels of reliability were observed between the timing gates and the app for the measurement of the 6 different trials of each participant (Timing gates: Intraclass correlation coefficient (ICC) = 0.651–0.747, Coefficient of variation (CV) = 2.6–3.5%; CODTimer: ICC = 0.671–0.840, CV = 2.2–3.2%). The results of the present study show that change of direction performance can be measured in a valid, reliable way using a novel iPhone app.