Linear Position Transducer Research Articles

Explosive Leg Press Stretch-Shortening Potentiation

The importance of understanding how the stretch-shortening cycle (SSC) may enhance muscle performance over concentric-only (CO) contractions has great relevance to sport scientists, coaches, and athletes. Potentiation is the enhancement that occurs in the concentric phase of the SSC as compared to performing concentric-only contractions (contractions with no immediate preceding eccentric contractions). PURPOSE: To determine ballistic leg press potentiation of force, acceleration, velocity, and power at six leg press sled time intervals across the concentric range of motion (ROM) and at ten time intervals across the initial 200 ms of the concentric phase of contraction. We also sought to determine relationships between specific potentiation variables and the time of the amortization phase and eccentric force during the last 100 ms of the eccentric phase of the SSC. METHODS: Twenty-one male competitive distance runners (age: 31 ± 5 yrs; weight: 80 ± 11 kg) performed SSC and CO leg press ballistic throws with a load of 150% bodyweight on a 35 degree angle leg press machine. The machine connected to a cable-extension linear position transducer that was interfaced with a data acquisition system utilizing custom software. After familiarization, warm-ups, and practice trials subjects performed 3 SSC and 3 CO leg press ballistic throws with a large amplitude concentric ROM at the knee from 90 to 0 degrees. Test-retest evaluations of muscle performance variables for this study have a coefficient of variation ranging from 1.7% to 4.3%. RESULTS: Across the full concentric ROM, differences from zero (p<0.05) existed with 1) potentiated mean force and acceleration only at the first 1/6th time interval over the concentric phase, and 2) potentiated mean velocity and power at all leg press time intervals over the entire concentric phase with the exception of power over the last 1/6 time interval (closest to full knee extension). Across the initial 200ms of the concentric phase, differences from zero (p<0.05) existed with 1) potentiated mean force and acceleration up until the time intervals greater than 160 ms, and 2) potentiated mean velocity and power for all time intervals over the first 200ms of the concentric phase. There were significant correlations between eccentric mean force measured during the last 100ms of the eccentric phase and potentiated average mean force during the initial 200ms of the concentric phase (r = 0.44, p<0.05) and potentiated average mean power across the full concentric ROM (r = 0.62, p < 0.01). CONCLUSIONS: Findings indicate large amplitude SSC leg press ballistic throws potentiate mean force, acceleration, velocity, and power early in the concentric ROM, and that potentiated mean velocity and power are conserved throughout the full concentric ROM with the exception of power at the very end of the range. Eccentric mean force measured during the last 100ms of the stretching phase is positively related to potentiated average mean force during the initial 200ms of the concentric phase and potentiated average mean power across the full concentric ROM. Practical Applications: To facilitate positive effects on potentiated concentric force and power during large amplitude SSC movements like an explosive leg press exercise, it may be beneficial to specifically train to improve force late in the eccentric phase of the SSC.

Experimental Investigations of Backfill Conditions on the Performance of High-Density Polyethelene Pipes

In this study, a series of laboratory tests on 100-mm-diameter high-density polyethylene (HDPE) 100 PE flexible pipe buried in poorly graded Sile quartz sand with different relative densities are described. The laboratory tests were performed in a 40-mm-thick plexiglass fronted test tank that replicated a classical trench section in field conditions. The HDPE flexible pipe was positioned against the glass with its longitudinal axis perpendicular to the glass. This allowed direct observation of the backfill–pipe interactions. Three high-definition photogrammetric cameras were used to capture the photogrammetric images through the glass allowing the discrete measurement and image processing of the deformation patterns of the pipe conduit during the pipe installation and incremental surcharge loading. Vertical loads were applied in increments of 10–150 kPa using air pressure membranes. Electric resistant strain gauges measured the bending moments of the pipe walls under vertical surcharge loadings. For each loading step, the vertical deformation of the pipe crown was also measured using linear position transducers. According to the test results, it is understood that the installation technique and backfill relative density have an important effect on circumferential strains, performance, and deformation characteristics of HDPE pipes. It was also observed that close-range image processing is a very simple and appropriate method for measuring three-dimensional pipe deformations under various conditions.

Effect of Instantaneous Performance Feedback During 6 Weeks of Velocity-Based Resistance Training on Sport-Specific Performance Tests

The purpose of this study was to investigate the effect of instantaneous performance feedback (peak velocity) provided after each repetition of squat jump exercises over a 6-week training block on sport-specific performance tests. Thirteen professional rugby players were randomly assigned to 1 of 2 groups, feedback (n = 7) and non-feedback (n = 6). Both groups completed a 6-week training program (3 sessions per week) comprising exercises typical of their normal preseason conditioning program. Squat jumps were performed in 2 of the 3 sessions each week during which both groups performed 3 sets of 3 concentric squat jumps using a barbell with an absolute load of 40 kg. Participants in group 1 were given real-time feedback on peak velocity of the squat jump at the completion of each repetition using a linear position transducer and customized software, whereas those in group 2 did not receive any feedback. Pre and posttesting consisted of vertical jump, horizontal jump, and 10-/20-/30-m timed sprints. The relative magnitude (effect size) of the training effects for all performance tests was found to be small (0.18-0.28), except for the 30-m sprint performance, which was moderate (0.46). The probabilities that the use of feedback during squat jump training for 6 weeks was beneficial to increasing performance of sport-specific tests was 45% for vertical jump, 65% for 10-m sprints, 49% for 20-m sprints, 83% for horizontal jump, and 99% for 30-m sprints. In addition to improvements in the performance of sport-specific tests, suggesting the potential for greater adaptation and larger training effects, the provision of feedback may also be used in applications around performance targets and thresholds during training.

Effect of Different Types of Conditioning Contraction on Upper Body Postactivation Potentiation

Muscle contractions preceding an activity can result in increased force generation (postactivation potentiation [PAP]). Although the type of muscular contractions could affect subsequent strength and power performance, little information exists on their effects. The purpose of this study was to examine PAP effects produced by isometric (ISO), concentric (CON), eccentric (ECC), or concentric-eccentric (DYN) conditioning contractions on upper body force and power performance. Ten male, competitive rugby players (mean ± SD: age 20.4 ± 0.8 years, height 177.0 ± 8.1 cm, body mass 90.2 ± 13.8 kg) performed a ballistic bench press throw (BBPT) followed by a 10-minute rest and one of the conditioning contractions. After a 12-minute rest, the subjects performed another BBPT (post-BBPT). The conditioning contractions, applied on separate days and in counterbalanced randomized order, were a 7-second isometric barbell bench press for ISO and 1 set of 3 bench press repetitions at 3 repetition maximum for CON, ECC, and DYN (each repetition lasting 2 seconds for CON and ECC, overall execution time <7 seconds for DYN). Peak power (Ppeak), peak force (Fpeak), maximum distance (Dmax) and rate of force development (RFD) were measured using a linear position transducer. Electromyography (EMG) of the pectoralis major and triceps brachii was also recorded. The ISO produced significantly higher Ppeak (587 ± 116 and 605 ± 126 W for pre- and post-BBPT, respectively; p < 0.05). No significant differences in Ppeak were revealed for CON, ECC, and DYN (p > 0.05), and no significant differences existed in Fpeak, Dmax, and RFD for ISO, CON, ECC, and DYN (p > 0.05). Finally, EMG was not significantly different between pre- and post-BBPT for any of the conditioning contractions (p > 0.05). Isometric contractions appear to be the only conditioning contractions increasing upper body power output after long resting periods.

Comparison of Kinetic Variables and Muscle Activity During a Squat vs. a Box Squat

The purpose of this investigation was to determine if there was a difference in kinetic variables and muscle activity when comparing a squat to a box squat. A box squat removes the stretch-shortening cycle component from the squat, and thus, the possible influence of the box squat on concentric phase performance is of interest. Eight resistance trained men (Height: 179.61 ± 13.43 cm; Body Mass: 107.65 ± 29.79 kg; Age: 24.77 ± 3.22 years; 1 repetition maximum [1RM]: 200.11 ± 58.91 kg) performed 1 repetition of squats and box squats using 60, 70, and 80% of their 1RM in a randomized fashion. Subjects completed the movement while standing on a force plate and with 2 linear position transducers attached to the bar. Force and velocity were used to calculate power. Peak force and peak power were determined from the force-time and power-time curves during the concentric phase of the lift. Muscle activity (electromyography) was recorded from the vastus lateralis, vastus medialis, biceps femoris, and longissimus. Results indicate that peak force and peak power are similar between the squat and box squat. However, during the 70% of 1RM trials, the squat resulted in a significantly lower peak force in comparison to the box squat (squat = 3,269 ± 573 N, box squat = 3,364 ± 575 N). In addition, during the 80% of 1RM trials, the squat resulted in significantly lower peak power in comparison to the box squat (squat = 2,050 ± 486 W, box squat = 2,197 ± 544 W). Muscle activity was generally higher during the squat in comparison to the box squat. In conclusion, minimal differences were observed in kinetic variables and muscle activity between the squat and box squat. Removing the stretch-shortening cycle during the squat (using a box) appears to have limited negative consequences on performance.

Validity of two kinematic systems for calculating force and power during squat jumps

Force and power are key exercise outputs in research and training practice. The direct acquisition of this kinetic data typically requires a force plate, which is not always practical and cost-effective, and generally limited to laboratory-based settings. Thus, kinematic systems (eg, linear position transducers, accelerometers) are becoming increasingly popular as tools for calculating force and power in situ during exercise. The aim was to assess the validity of a commercial linear position transducer and accelerometer for calculating force and power during squat jumps. Seven healthy males performed 2×single repetition squat jumps with four loads (20 kg, 40 kg, 60 kg and 80 kg). The squats were performed on top of a Kistler force plate. A commercial linear position transducer (Gymaware (GYM)) and accelerometer (Myotest (MYO)) were attached to the bar to assess concentric peak force (PF) and peak power (PP), based on the combined mass of the external load and each subject. Data were pooled across all loads for analysis. The PF and PP data from the GYM and MYO systems were strongly correlated with the force plate data (r=0.84-0.93, p&lt;0.001) and also with each other (r=0.90-0.97, p&lt;0.001). The mean PF and/or PP values calculated from the GYM and MYO systems were found to be 4.5%-6.5% higher than the measured values from the force plate (p&lt;0.01). The PF and PP data from the linear position transducer and accelerometer showed strong relative validity compared to the force plate, but some differences in absolute validity were noted. The two kinematic systems provide other benefits (eg, portability, ease of use, cost effectiveness) for assessing PF and PP during squat jumps or similar isoinertial exercises.

Using Additional Eccentric Loads to Increase Concentric Performance in the Bench Throw

The purpose of this study was to determine whether superior concentric performance could be achieved in the bench throw with the use of additional eccentric loads. Fourteen male subjects performed bench throws in a smith machine with an eccentric-concentric load of 40-kg (40-40), and 40-kg concentric with additional eccentric loads of 20 (60-40), 30 (70-40), and 40 kg (80-40). A linear position transducer was used to record displacement-time characteristics, allowing for determination of maximum displacement of the barbell. Differences between the conditions were accepted when p < 0.05. Barbell displacements in the 60- to 40-, 70- to 40-, and 80- to 40-kg eccentric-concentric conditions were all significantly greater than for the 40- to 40-kg eccentric-concentric equated load condition, but no significant difference was observed between each eccentric-concentric load condition. Superior concentric peak barbell displacement can be achieved with additional eccentric loads in the 40-kg bench throw when compared to an equated eccentric-concentric 40- to 40-kg condition, possibly because of greater muscle tension and crossbridging during the eccentric action. Strength and conditioning coaches can use accentuated eccentric load bench throws to elicit greater concentric bench throw performance in athletes.

Effect of Absolute and Relative Loading on Muscle Activity During Stable and Unstable Squatting

The purpose of this investigation was to determine the effect of stable and unstable conditions on one repetition maximum strength and muscle activity during dynamic squatting using absolute and relative loading. Ten recreationally weight-trained males participated in this study (age = 24.1 +/- 2.0 y, height = 178.0 +/- 5.6 cm, body mass = 83.7 +/- 13.4 kg, 1RM/body mass = 1.53 +/- 0.31), which involved two laboratory sessions separated by 1 wk. Linear position transducers were used to track bar displacement while subjects stood on a force plate for all trials. Vastus lateralis (VL), biceps femoris (BF) and erector spinae (L1) muscle activity (average integrated EMG [IEMG]) was also recorded during all trials. During the first session subjects complete a one repetition maximum test in a stable dynamic squat (S1RM = 128.0 +/- 31.4 kg) and an unstable dynamic squat (U1RM = 83.8 +/- 17.3 kg) in a randomized order with a 30-min rest period between conditions. The second session consisted of the performance of three trials each for 12 different conditions (unstable and stable squats using three different absolute loads [six conditions] and unstable and stable squats using three different relative loads [six conditions]). Results revealed a statistically significant difference between S1RM and U1RM values (P < or = .05). The stable trials resulted in the same or a significantly higher value for VL, BF and L1 muscle activity in comparison with the unstable trials for all twelve conditions. Unstable squatting is of equal or less (depending on the loading condition) benefit to improving or maximizing muscle activity during resistance exercise.

Comparative Force Outputs From Non-Centered Accelerometers During Loaded Barbell Jump Squats

The direct acquisition of ground reaction force data during isoinertial resistance tasks typically requires a force platform. As this is not always practical, alternative devices have been used to estimate dynamic force by directly measuring other variables and then using inverse dynamics to calculate it. For example, linear position and linear velocity transducers have been tethered to bars and used for this purpose. Recently, a dynamometer incorporating an accelerometer and no tether became available for this application. However, since barbell equipment inherently allows for asymmetrical movement through multiple planes, it follows that force output may differ depending upon bar orientation, especially deviations from horizontal. Furthermore, differences related to dynamometer placement and/or variations in the lifting movement pattern could be problematic if training-induced changes are to be monitored. To determine if peak force differed during barbell jump squats using non-centered accelerometer placements. 52 subjects (27 women & 25 men) with squat training experience were recruited from a university population. Subjects performed duplicate loadspectrum countermovement jump squats (CMJ) and static jump squats (SJ) (20%, 30% & 40% of their back squat 1RM) on two separate days in a counterbalanced sequence. A triaxial accelerometer device was directly affixed to each end of the barbell midway between the lateral-most aspect of the shoulder and the thumb side of each hand. Acceleration data were downsampled from 1.5 KHz to 500Hz by averaging every 3 data points. These data were then low-pass filtered (4th order Butterworth) with a cutoff frequency of 10Hz via proprietary software. Force was determined via inverse dynamics with mass considered the sum of body and barbell weights. Peak force data from the two dynamometers were always obtained from the same trial. Paired t-tests were used for data analysis. Dynamometers provided similar peak force values for both CMJ and SJ at 20% and 40% 1RM loads (p > .05) and different values at the 30% 1RM load (p < .01). Mean differences (20, 30, & 40%, respectively) for the CMJ were 9.8N, 15.1N, 8.1N and for the SJ were -1.5N, 15.4N, 5.9N (Table 1). For relatively light countermovement and static jump squats, dynamometer placement on both ends of barbell may result in differential peak force output. It appears that accelerometer placement during jump squats should either be as close as possible to the center of the bar or a squat machine with a horizontally-fixed bar should be used. Although not tested herein, it is likely that linear position and linear velocity transducers would have the identical constraints. As contiguous accelerometer placement was not tried herein, it is unclear what, if any, contribution the dynamometers made to measurement error.

Effect Of Absolute And Relative Loading On Muscle Activity During Stable And Unstable Squatting

Purpose: The purpose of this investigation was to determine the effect of stable and unstable conditions on one repetition maximum strength and muscle activity during dynamic squatting using absolute and relative loading. Methods: Ten recreationally weight-trained males participated in this study (age = 24.1 ± 2.0 y, height = 178.0 ± 5.6 cm, body mass = 83.7 ± 13.4 kg, 1RM/body mass = 1.53 ± 0.31), which involved two laboratory sessions separated by 1 wk. Linear position transducers were used to track bar displacement while subjects stood on a force plate for all trials. Vastus lateralis (VL), biceps femoris (BF) and erector spinae (L1) muscle activity (average integrated EMG [IEMG]) was also recorded during all trials. During the frst session subjects complete a one repetition maximum test in a stable dynamic squat (S1RM = 128.0 ± 31.4 kg) and an unstable dynamic squat (U1RM = 83.8 ± 17.3 kg) in a randomized order with a 30-min rest period between conditions. The second session consisted of the performan...

Effect Of Squat Depth On Vertical Jump Performance Variables

Maximizing vertical jump performance is a critical element to success in many athletic situations. Certain individual kinetic and kinematic variables may have greater contributing roles to vertical jump outcome. Squat depth prior to the initiation of the concentric motion would seem to have an impact on these variables, yet there are limited investigations comparing squat depths and vertical jump performance variables. To determine the effect of squat depth on vertical jump performance variables. Seven recreationally-trained males (Height = 177.9 ± 4.7 cm, Weight = 83.6 ± 10.5 kg) performed static jumps (SJ) and countermovement jumps (CMJ) from six squat depths (0.15 m, 0.30 m, 0.45 m, 0.60 m, 0.75 m and preferred depth) in a randomized order. Subjects held a weightless bar across their upper back attached to two linear position transducers ensuring the bar did not move independently of the body while standing on a force plate. Peak force (PF), impulse (I) and jump height (JH) were measured. Significant differences were found between 0.15 m squat depth and other squat depths (0.30 m, 0.45 m, 0.60 m and 0.75 m) for both the SJ and CMJ for PF, I and JH. SJ PF was significantly higher (p < 0.05) at 0.15m (2683.3 ± 281.5 N) in comparison to 0.30m (2285.3 ± 239.6 N), 0.45m (1992.4 ± 190.3 N), 0.60m (1842.5 ± 181.3 N), 0.75m (1761.9 ± 214.2 N). SJ I was significantly lower at 0.15 m (282.3 ± 53.9 N-s) in comparison to 0.30m (377.8 ± 53.3 N-s), 0.45 m (453.0 ± 41.2 N-s), 0.60 m (526.0 ± 62.5 N-s), 0.75 m (597.3 ± 58.1 N-s). SJ JH was significantly lower at 0.15 m (0.275 ± 0.046 m) in comparison to 0.30 m (0.374 ± 0.074 m), 0.45 m (0.447 ± 0.070 m), 0.60 m (0.477 ± 0.078 m), 0.75 m (0.490 ± 0.070 m). CMJ PF was significantly higher at 0.15 m (3068.9 ± 455.6 N) in comparison to 0.30 m (2389.1 ± 294.7 N), 0.45 m (2082.8 ± 266.1 N), 0.60 m (1912.8 ± 228.0 N), 0.75 m (1709.7 ± 210.5 N). CMJ I was significantly lower at 0.15 m (566.9 ± 96.7 N-s) in comparison to 0.30m (816.4 ± 119.3 N-s), 0.45m (930.3 ± 128.1 N-s), 0.60m (1060.6 ± 137.1 N-s), 0.75 m (1123.9 ± 136.2 N-s). CMJ JH was significantly lower at 0.15 m (0.311 ± 0.064 m) in comparison to 0.30 m (0.444 ± 0.055 m), 0.45 m (0.475 ± 0.053 m), 0.60 m (0.508 ± 0.078 m), 0.75m (0.540 ± 0.060 m). For both SJ and CMJ preferred squat depth occurred at the depth that maximized displacement (SJ-0.443 ± 0.060 m, CMJ-0.533 ± 0.037 m) while minimizing contact time (SJ- 253.7 ± 40.6 ms, CMJ-716.9 ± 97.4 ms). A shallow squat depth resulted in higher PF, lower I, and lower JH than squat depths of 0.30 m and lower. High PF values and low I values did not correspond with increased jump height. To maximize jump height a squat depth of at least 0.30m should be utilized for both CMJ and SJ. When self-selecting squat depth, subjects chose a depth that would produce the highest displacement with the shortest amount of contact time. While a shallow squat depth may decrease the time needed to initiate a jump during competition, the result will be a decrease in jump height. While decreased contact time may be required in competition, if the situation allows for an increased contact time it may result in greater jump height which could influence performance.

Effects Of Six Weeks Periodized Squat Training With Or Without Whole Body Vibration Upon The Relationship Between Isometric And Dynamic Performance

Resistance training interventions aimed at increasing lower body power and rates of force development have produced varying results. Potentially, the use of WBLFV in between sets of resistance training may increase high-threshold motor unit recruitment and synchronization leading to greater adaptations in both isometric and dynamic performance. The relationship between isometric force/time characteristics and dynamic performance and their respective changes in response to resistance training is of practical importance to strength and conditioning practitioners. To determine the effects of applying whole body vibration prior to and then intermittently between sets of Smith Machine squats upon training induced changes in isometric and dynamic performance and their relationships to one another. Twenty four recreationally resistance trained men were randomly assigned to one of two groups, resistance only (SQT n = 11), or resistance plus whole body vibration (SQTV n = 13). An isometric squat test as well as Squat Jumps (SQJ) and Depth Jumps (DJ) were performed prior to, and following a six-week, periodized Smith Machine squat program. WBLFV was applied 180 s prior to the first work set (50Hz 2-4mm, 30 s) and intermittently (50Hz 4-6mm, 3 × 10 s, 60s between exposures) within a 240s inter-set rest period. Subjects were instructed to assume a quarter squat posture while positioning their feet directly under their center of mass which was modified using a hand held goniometer to a knee angle of 135 ± 5°. Measures of isometric force (N) and isometric rates of force development (N·s−1) were recorded from the onset of contraction (F0) to time points corresponding to F30ms, F80ms, F250ms, Force at initial peak (Finitial), Force at 50% of MVC (MVC50) Time Finitial (ms) as well as the Peak Isometric Force (MVCp) and Peak Isometric Rate of Force Development (PISORFD). Squat jumps were performed with a 20kg Olympic barbell with a linear position transducer attached while the DJ utilized body mass as resistance while dropping from a height of 30cm onto a switch mat. Measures recorded during jumps included jump height (cm) peak power (PMax,W), peak power per kg of body mass (PMax/kg, W/kg) and mean power (Pav,W) for both jump conditions. Correlation matrices matching isometric force/time variables and dynamic (SQJ, DJ) performance within group between weeks 1 and 7(Pre- Post training) revealed multiple significant positive, and negative correlations (p = *<.05 and**<.001, range, r = −.624 to .859). A greater total amount of positive correlations were seen for SQTV (24) compared to SQT (2). Correlation coefficients (r) calculated between percent change (%Δ) scores for similar variables revealed small to moderate r values with the only significant correlation seen for the SQTV group between F30ms and DJ height (cm) (r = −.589, R2 = −.347, p <.05). More positive correlations were seen for isometric and dynamic %Δ variables that for SQTV (9) compared to SQT (7). The addition of WBLFV to the SQTVgroup appeared to effect neuro-muscular training adaptation differently from SQT as reflected in the percent change relationship between isometric and dynamic performance measures following six weeks of exposure. WBLFV may help facilitate early phase adaptations to resistance exercise with a tendency to improve early force time components of isometric and dynamic performance.

High Reliability Of Jump Performance Assessed With A Linear Transducer In Elite Track And Field Athletes

Although the countermovement vertical jump (CMJ) has been extensively used, data about reliability parameters on a large subject sample (∼50) of elite athletes are limited. PURPOSE: To determine the reliability of CMJ performance in a large sample of track and field top athletes using a linear transducer. METHODS: A group of 48 elite male sprinters and long-jumpers volunteered to participate in this study. Subjects performed three trials with 3 minutes of rest between each CMJ. This was accomplished by measuring jump performance using a linear transducer and a force platform simultaneously. The relationships between force-time dependent variables and CMJ performance were examined during the concentric phase using a Smith machine. RESULTS: The present study demonstrated high intraclass correlations (ICC) values for maximum rate of force development (RFDmax) accessed with linear transducer, however, the coefficient of variation (CV) was somewhat high (15-17%). Nevertheless, ICC of peak force (PF) and the maximum power measured with force platform were very high. The maximum negative velocity presents a somewhat smaller but likewise high degree of stability, although the CV is slightly high (9.9%). The trial-to-trial reliability of the CMJ measured by the force platform gave an ICC of 0.87-0.97 for PF, maximum power and maximum negative velocity. Similar ICCs of 0.93-0.98 for RFDmax, PF, and for rate of force development at PF were observed by the linear transducer. The CVs were 3.6-17% and 5.8-9.9% with force platform and with linear transducer, respectively. CONCLUSIONS: The present findings showed that the calculations derived from the linear transducer synchronized with a force platform were very similar and hence provided evidence of the reliability of this method in elite track and field athletes. Moreover, this method suggests that the linear position transducer offers a cost-effective, versatile, and valid means for the measurement of force in track and field top athletes.

Validité et reproductibilité d’un dynamomètre inertiel basé sur l’accélérométrie

Introduction The purpose of this study was to investigate the validity and reliability of an inertial dynamometer using accelerometry. Methods Fourteen subjects were tested during three successive sessions at four increasing loads (30, 50, 70 and 95% of the 1RM). Maximal force, velocity and power performances were simultaneously assessed by the Myotest (Myotest S.A., Switzerland), an inertial dynamometer using accelerometry, and by another control valid dynamometer witch combine accelerometer and linear position transducer. At three first loads, only minor differences appeared in between both dynamometers, correlations were excellent and coefficients of variation were good and similar. However, at 95% of the 1RM, Myotest validity and reliability became insufficient. Conclusion Bench press inertial assessment with accelerometer appeared valid and reliable at 30, 50 and 70% of the 1RM, but not at 95% of the 1RM.

Increasing Compliance to Instructions in the Squat Jump

The purposes of this investigation were to evaluate the occurrence of a small amplitude counter-movement (SACM) in SJ (squat jump) trials of elite athletes to determine the efficacy of gross observation and the use of a portable position transducer to determine whether or not a SACM occurred. The subjects (N = 30, 20.1 +/- 3.0 years, 199.0 +/- 8.4 cm, and 87.2 +/- 9.5 kg) were a combination of high-performance (National Team) and elite athletes (Olympian) from the sports of athletics, swimming, and volleyball. All subjects performed SJ trials on a force platform, with a linear position transducer attached to a bar placed across the shoulders. Subjects performed the SJ from a depth that allowed for a 90 degrees knee angle, with the subject's instructed to maintain a 3-second isometric hold preceding the concentric action of the jump. One hundred twenty-five SJ trials were observed for a SACM and analyzed (using the force plate data and position transducer data) for a SACM. Of the 125 SJ trials, 69 trials (55.2%) were observed to have a SACM by the researchers. In the remaining 56 trials, 43 of these trials contained a force unload (>/=10% body mass) before initiation of the concentric action, indicating a SACM. Of the 119 SJ trials where a force unload was observed and detected by the force-time graph, 118 (99.2%) of these trials also showed a change in displacement using the displacement-time graph from the linear position transducer. The results of this study indicate that achieving compliance to protocol in the SJ is difficult, and that gross observation is inadequate in detecting a SACM in the SJ. From a practical perspective, these results suggest that using a force plate or a linear position transducer would allow the strength and conditioning coach to ensure compliance to instructions in the SJ.

Effects of Intensified Military Field Training on Jumping Performance

A sensitive, reliable, field-expedient test may be valuable for monitoring interventions during periods of anticipated physical performance decline. The purpose of this study was to determine the capabilities of unloaded jumping tests for detecting decrements in physical performance following eight days of military sustained operations. Twenty-nine U. S. Marines (24 +/- 1 y; 180 +/- 6 cm; 82.5 +/- 8.2 kg) performed 1, 5 and 30 repetition(s) of unloaded countermovement jumps (UJ) before and after eight days of sustained operations (SUSOPS). Jump performance data was collected simultaneously using a switch mat (SM) and a linear position transducer (LPT). Jump height (m) and power (W) were highest using 1 UJ and declined 4.9 and 8.9%, respectively after SUSOPS. Jump power (JP) declined progressively over 30 UJ (20%). Five UJ offered no advantages over 1 UJ and was inadequate to examine changes in muscle fatigability (pre: 1294 +/- 138 W; post: 1250 +/- 165 W). The SM and a LPT were in agreement and had a high correlation (r = 0.92). One UJ was a sensitive, easy to implement test for monitoring the collective impact of high physical, nutritional, cognitive, and environmental stress on an individuals' physical performance before and after 8 days of SUSOPS, suggesting decrements in physical performance associated with overreaching can be detected by simply administered field-expedient jumping tests.

Validation of Power Measurement Techniques in Dynamic Lower Body Resistance Exercises

The objective of this study was to investigate the validity of power measurement techniques utilizing various kinematic and kinetic devices during the jump squat (JS), squat (S) and power clean (PC). Ten Division I male athletes were assessed for power output across various intensities: 0, 12, 27, 42, 56, 71, and 85% of one repetition maximum strength (1RM) in the JS and S and 30, 40, 50, 60, 70, 80, and 90% of 1RM in the PC. During the execution of each lift, six different data collection systems were utilized; (1) one linear position transducer (1-LPT); (2) one linear position transducer with the system mass representing the force (1-LPT+MASS); (3) two linear position transducers (2-LPT); (4) the force plate (FP); (5) one linear position transducer and a force plate (1-LPT+FP); (6) two linear position transducers and a force place (2-LPT+FP). Kinetic and kinematic variables calculated using the six methodologies were compared. Vertical power, force, and velocity differed significantly between 2-LPT+FP and 1-LPT, 1-LPT+MASS, 2-LPT, and FP methodologies across various intensities throughout the JS, S, and PC. These differences affected the load-power relationship and resulted in the transfer of the optimal load to a number of different intensities. This examination clearly indicates that data collection and analysis procedures influence the power output calculated as well as the load-power relationship of dynamic lower body movements.

METHODOLOGICAL CONCERNS FOR DETERMINING POWER OUTPUT IN THE JUMP SQUAT

The purpose of this study was to investigate the validity of power measurement techniques during the jump squat (JS) utilizing various combinations of a force plate and linear position transducer (LPT) devices. Nine men with at least 6 months of prior resistance training experience participated in this acute investigation. One repetition maximums (1RM) in the squat were determined, followed by JS testing under 2 loading conditions (30% of 1RM [JS30] and 90% of 1RM [JS90]). Three different techniques were used simultaneously in data collection: (a) 1 linear position transducer (1-LPT); (b) 1 linear position transducer and a force plate (1-LPT + FP); and (c) 2 linear position transducers and a force place (2-LPT + FP). Vertical velocity-, force-, and power-time curves were calculated for each lift using these methodologies and were compared. Peak force and peak power were overestimated by 1-LPT in both JS30 and JS90 compared with 2-LPT + FP and 1-LPT + FP (p ≤ 0.05). Peak power determined by 2-LPT + FP was significantly higher than that determined by 1-LPT + FP under the JS90 loading condition. Peak vertical velocity determined by 2-LPT + FP was significantly lower than that determined by either 1-LPT and 1-LPT + FP in JS90. This investigation indicates that peak power and the timing of power output in the jump squat varies according to the measurement technique utilized. The 1-LPT methodology is not a valid means of determining power output in the jump squat. Furthermore, the 1-LPT + FP method may not accurately represent power output in free weight movements that involve a significant amount of horizontal motion.

Predicting Obstacle Course Performance of Women Using Less Complex Physiological and Performance Tests

Obstacle courses are used to test the readiness of soldiers, firefighters, and law enforcement officers to meet the physical challenges they are likely to encounter on the battlefield and in other occupational settings. However, obstacle courses are expensive to build and maintain and are not always available. PURPOSE: To predict obstacle course performance from less complex physical performance and physiological tests. METHODS: After 6 rounds of practice to stabilize obstacle course performance, 48 females (mean±SD: age 20.2± 1.85 yrs, height 1.65± 0.07 m, body mass 63.9± 7.01 kg) traversed an 8 station obstacle course (hurdles, cone weave, low crawl, pipe traversal wall, sprint, mantle and stair climb) as quickly as possible (66.1± 8.1 s). Subjects performed a battery of tests including anthropometry, DEXA body composition tests, 2-mile loaded and also unloaded timed runs, a 50 m simulated casualty recovery test and 1 repetition maximum (1RM) bench press and squat. Bench press throws and squat jumps with 30% of the subject's 1RM load were performed in which a computer with a compact linear position transducer was used to measure the peak height, velocity and power. Stepwise multiple linear regression analyses were run using these variables. RESULTS: Body composition and anthropometric variables failed as predictors and the following equation (p<0.001) using maximal 2-mile run for time (min), and the squat jump peak vertical velocity (SJPV, m.s-1) was the best predictor of obstacle course performance. Time(s) = 99.4 - 21.00(SJPV) + 0.795(2 Mile Run Time), R=0.738, R2= 0.544, SEE=5.6 CONCLUSION: The 2-mile run has been shown as a strong predictor of aerobic capacity (Mello,1988), the 1RM squat is an easy, reliable test that can be done with minimal resources and the squat jump peak velocity test, while requiring a computer and a position transducer, can be performed in any weight room. Ironically, anthropometry and body composition variables were poor predictors. It is interesting that an endurance test of 13.8-28.3 min. duration and an explosive jump test are the strongest predictors of a 66.1 s long task. Using simple performance tests for predicting obstacle course performance can help determine the readiness status of workers in physically demanding occupations when a lab or obstacle course is not available.

Methodological Concerns for Determining Power Output in the Jump Squat

The purpose of this study was to investigate the validity of power measurement techniques during the jump squat (JS) utilizing various combinations of a force plate and linear position transducer (LPT) devices. Nine men with at least 6 months of prior resistance training experience participated in this acute investigation. One repetition maximums (1RM) in the squat were determined, followed by JS testing under 2 loading conditions (30% of 1RM [JS30] and 90% of 1RM [JS90]). Three different techniques were used simultaneously in data collection: (a) 1 linear position transducer (1-LPT); (b) 1 linear position transducer and a force plate (1-LPT + FP); and (c) 2 linear position transducers and a force place (2-LPT + FP). Vertical velocity-, force-, and power-time curves were calculated for each lift using these methodologies and were compared. Peak force and peak power were overestimated by 1-LPT in both JS30 and JS90 compared with 2-LPT + FP and 1-LPT + FP (p <or= 0.05). Peak power determined by 2-LPT + FP was significantly higher than that determined by 1-LPT + FP under the JS90 loading condition. Peak vertical velocity determined by 2-LPT + FP was significantly lower than that determined by either 1-LPT and 1-LPT + FP in JS90. This investigation indicates that peak power and the timing of power output in the jump squat varies according to the measurement technique utilized. The 1-LPT methodology is not a valid means of determining power output in the jump squat. Furthermore, the 1-LPT + FP method may not accurately represent power output in free weight movements that involve a significant amount of horizontal motion.