Comparison of four different methods to measure power output during the hang power clean and the weighted jump squat

Measurement of power output during resistance training is becoming ubiquitous in strength and conditioning programs, but there is great variation in the methods used. The main purposes of this study were to compare the power output values obtained from 4 different methods and to examine the relationships between these values. Male semiprofessional Australian rules football players (n = 30) performed hang power clean and weighted jump squat while ground reaction force (GRF)-time data and barbell displacement-time data were sampled simultaneously using a force platform and a linear position transducer attached to the barbell. Peak and mean power applied to the barbell was obtained from barbell displacement-time data (method 1). Peak and mean power applied to the system (barbell + lifter) was obtained from 3 other methods: (a) using GRF-time data (method 2), (b) using barbell displacement-time data (method 3), and (c) using both barbell displacement-time data and GRF-time data (method 4). The peak power values (W) obtained from methods 1, 2, 3, and 4 were (mean +/- SD) 1,644 +/- 295, 3,079 +/- 638, 3,821 +/- 917, and 4,017 +/- 833 in hang power clean and 1,184 +/- 115, 3,866 +/- 451, 3,567 +/- 494, and 4,427 +/- 557 in weighted jump squat. There were significant differences between power output values obtained from method 1 vs. methods 2, 3, and 4, as well as method 2 vs. methods 3 and 4. The power output applied to the barbell and that applied to the system was significantly correlated (r = 0.65-0.81). As a practical application, it is important to understand the characteristics of each method and consider how power output should be measured during the hang power clean and the weighted jump squat.     

Influence of different relative intensities on power output during the hang power clean: identification of the optimal load

The influence of different relative intensities on power output was investigated in the present study in order to identify the optimal load that maximizes power output during the hang power clean. Fifteen men (age: 22.1 +/- 2.0 years, height: 180.1 +/- 6.3 cm, and body mass: 89.4 +/- 14.7 kg) performed the hang power cleans on a forceplate at 30-90% of one repetition maximum (1RM). Peak power was maximized at 70% 1RM, which was, however, not significantly different from peak power at 50, 60, 80, and 90% 1RM. Average power also was maximized at 70% 1RM, which was not significantly different from average power at 40, 50, 60, 80, and 90% 1RM. It was concluded that (a) the relative intensity had a significant influence on power output, and (b) power output can be maximized at a submaximal load during the hang power clean.     

Stroke volume response to progressive exercise in athletes engaged in different types of training

Using the impedance cardiography method, heart rate ( _c) matched changes on indexed stroke volume (SI) and cardiac output (CI) were compared in subjects engaged in different types of training. The subjects consisted of untrained controls (C), volleyball players (VB) who spent about half of their training time (360 min · week^–1) doing anaerobic conditioning exercises and who had a maximal oxygen uptake ( ) 41% higher than the controls, and distance runners (D) who spent all their training time (366 min·week^–1) doing aerobic conditioning exercises and who had a 26% higher than VB. The subjects performed progressive submaximal cycle ergometer exercise (10 W·min^–1) up to _c of 150 beats·min^–1. In group C, SI had increased significantly (P<0.05) at _c of 90 beats·min^–1 ( + 32%) and maintained this difference up to 110 beats·min^–1, only to return to resting values on reaching 130 beats·min^–1 with no further changes. In group VB, SI peaked (+ 54%) at _c of 110 beats·min^–1, reaching a value significantly higher than that of group C, but decreased progressively to 22010 of the resting value on reaching 150 beats·min^–1. In group D, SI peaked at _c of 130 beats·min^–1 (+ 54%), reaching a value significantly higher than that of group VB, and showed no significant reduction with respect to this peak value on reaching 150 beats·min^–1. As a consequence, the mean CI increase per _c unit was progressively higher in VB than in C (+46%) and in D than in VB (+ 105%). It was concluded that thef _c value at which SI ceased to increase during incremental exercise was closely related to the endurance component in the training programme.     

Effect of interrepetition rest on power output in the power clean

The effect of interrepetition rest (IRR) periods on power output during performance of multiple sets of power cleans is unknown. It is possible that IRR periods may attenuate the decrease in power output commonly observed within multiple sets. This may be of benefit for maximizing improvements in power with training. This investigation involved 10 college-aged men with proficiency in weightlifting. The subjects performed 3 sets of 6 repetitions of power cleans at 80% of their 1 repetition maximum with 0 (P0), 20 (P20), or 40 seconds (P40) of IRR. Each protocol (P0, P20, P40) was performed in a randomized order on different days each separated by at least 72 hours. The subjects performed the power cleans while standing on a force plate with 2 linear position transducers attached to the bar. Peak power, force, and velocity were obtained for each repetition and set. Peak power significantly decreased by 15.7% during P0 in comparison with a decrease of 5.5% (R1: 4,303 ± 567 W, R6: 4,055 ± 582 W) during P20 and a decrease of 3.3% (R1: 4,549 ± 659 W, R6: 4,363 ± 476 W) during P40. Peak force significantly decreased by 7.3% (R1: 2,861 ± 247 N, R6: 2,657 ± 225 N) during P0 in comparison with a decrease of 2.7% (R1: 2,811 ± 327 N, R6: 2,730 ± 285 N) during P20 and an increase of 0.4% (R1: 2,861 ± 323 N, R6: 2,862 ± 280 N) during P40. Peak velocity significantly decreased by 10.2% (R1: 1.97 ± 0.15 m·s(-1), R6: 1.79 ± 0.11 m·s(-1)) during P0 in comparison with a decrease of 3.8% (R1: 1.89 ± 0.13 m·s(-1), R6: 1.82 ± 0.12 m·s(-1)) during P20 and a decrease of 1.7% (R1: 1.93 ± 0.17 m·s(-1), R6: 1.89 ± 0.14 m·s(-1)) during P40. The results demonstrate that IRR periods allow for the maintenance of power in the power clean during a multiple set exercise protocol and that this may have implications for improved training adaptations.     

Ground reaction forces during the power clean

Identifying and understanding the key biomechanical factors that exemplify the power clean can provide athletes the proper tools needed to prevail at a competitive event. Therefore, the purpose of this study was to characterize and describe ground reaction forces (Fz) during the power clean lift. Three 60-Hz motion-detecting cameras and an AMTI force plate were used to collect data from 10 collegiate weightlifting men who performed a power clean at 60 and 70% of their last competitive maximum clean. The results revealed that a greater peak force (Fz) was produced during the second pull compared with the first pull and unweighted phases in both percentage lifts. As the system weight increased from 60 to 70%, the peak force (Fz) increased for the first pull and unweighted phases and decreased during the second pull phase. Learning the proper technique of the power clean may provide athletes the basic understanding needed to be competitive in a weightlifting or sporting event.     

Kinetic comparisons during variations of the power clean

Comfort, P, Allen, M, and Graham-Smith, P. Kinetic comparisons during variations of the power clean. J Strength Cond Res 25(12): 3269-3273, 2011-The aim of this investigation was to determine the differences in peak power, peak vertical ground reaction forces, and rate of force development (RFD) during variations of the power clean. Elite rugby league players (n = 16; age 22 ± 1.58 years; height 182.25 ± 2.81 cm; body mass 98.65 ± 7.52 kg) performed 1 set of 3 repetitions of the power clean, hang power clean, midthigh power clean, or midthigh clean pull, using 60% of 1 repetition maximum power clean, in a randomized order, while standing on a force platform. One-way analysis of variance with Bonferroni post hoc analysis revealed a significantly (p < 0.001) greater peak power output during the midthigh power clean (3,565.7 ± 410.6 W) and the midthigh clean pull (3,686.8 ± 386.5 W) compared with both the power clean (2,591.2 ± 645.5 W) and the hang power clean (3,183.6 ± 309.1 W), along with a significantly (p < 0.001) greater peak Fz during the midthigh power clean (2,813.8 ± 200.5 N) and the midthigh clean pull (2,901.3 ± 226.1 N) compared with both the power clean (2,264.1 ± 199.6 N) and the hang power clean (2,479.3 ± 267.6 N). The midthigh power clean (15,049.8 ± 4,415.7 N·s) and the midthigh clean pull (15,623.6 ± 3,114.4 N·s) also demonstrated significantly (p < 0.001) greater instantaneous RFD when compared with both the power clean (8,657.9 ± 2,746.6 N·s) and the hang power clean (10,314.4 ± 4,238.2 N·s). From the findings of this study, when training to maximize power, Fz, and RFD, the midthigh power clean and midthigh clean pull appear to be the most advantageous variations of the power clean to perform.     

Alteration of protein patterns in black rock inhabiting fungi as a response to different temperatures

Rock inhabiting fungi are among the most stress tolerant organisms on Earth. They are able to cope with different stressors determined by the typical conditions of bare rocks in hot and cold extreme environments. In this study first results of a system biological approach based on two-dimensional protein profiles are presented. Protein patterns of extremotolerant black fungi – Coniosporium perforans, Exophiala jeanselmei – and of the extremophilic fungus – Friedmanniomyces endolithicus – were compared with the cosmopolitan and mesophilic hyphomycete Penicillium chrysogenum in order to follow and determine changes in the expression pattern under different temperatures. The 2D protein gels indicated a temperature dependent qualitative change in all the tested strains. Whereas the reference strain P. chrysogenum expressed the highest number of proteins at 40 °C, thus exhibiting real signs of temperature induced reaction, black fungi, when exposed to temperatures far above their growth optimum, decreased the number of proteins indicating a down-regulation of their metabolism. Temperature of 1 °C led to an increased number of proteins in all of the analysed strains, with the exception of P. chrysogenum. These first results on temperature dependent reactions in rock inhabiting black fungi indicate a rather different strategy to cope with non-optimal temperature than in the mesophilic hyphomycete P. chrysogenum.     

Growth plate cartilage shows different strain patterns in response to static versus dynamic mechanical modulation

Longitudinal growth of long bones and vertebrae occurs in growth plate cartilage. This process is partly regulated by mechanical forces, which are one of the underlying reasons for progression of growth deformities such as idiopathic adolescent scoliosis and early-onset scoliosis. This concept of mechanical modulation of bone growth is also exploited in the development of fusionless treatments of these deformities. However, the optimal loading condition for the mechanical modulation of growth plate remains to be identified. The objective of this study was to evaluate the effects of in vitro static versus dynamic modulation and of dynamic loading parameters, such as frequency and amplitude, on the mechanical responses and histomorphology of growth plate explants. Growth plate explants from distal ulnae of 4-week-old swines were extracted and randomly distributed among six experimental groups: baseline (\(n=10\)), control (\(n=10\)), static (\(n=10\)) and dynamic (\(n=3\times 10\)). For static and dynamic groups, mechanical modulation was performed in vitro using an Indexed CartiGen bioreactor. A stress relaxation test combined with confocal microscopy and digital image correlation was used to characterize the mechanical responses of each explant in terms of peak stress, equilibrium stress, equilibrium modulus of elasticity and strain pattern. Histomorphometrical measurements were performed on toluidine blue tissue sections using a semi-automatic custom-developed MATLAB toolbox. Results suggest that compared to dynamic modulation, static modulation changes the strain pattern of the tissue and thus is more detrimental for tissue biomechanics, while the histomorphological parameters are not affected by mechanical modulation. Also, under dynamic modulation, changing the frequency or amplitude does not affect the biomechanical response of the tissue. Results of this study will be useful in finding optimal and non-damaging parameters for the mechanical modulation of growth plate in fusionless treatments.     

Biomechanical analysis of the knee during the power clean

To our knowledge, no scientific literature has examined the 3-dimensional forces acting at the knee joint during a power clean. Ten male weightlifting subjects (25.9 years, SD 3.54) performed 1 set of the power clean at 60 and 70% of their maximal collegiate level for 5 repetitions. The subjects displayed a large compressive, moderate anterior, and a small degree of lateral and medial force at the knee during both percentage lifts. The majority of these forces occurred during the second pull phase or the catching phase of the lift. Lifters with decreased weight/system weight percentages displayed a more efficient lift that placed less stress on the knees. This analysis may provide invaluable information in the assessment of weight percentages used for Olympic weightlifters throughout the training year. the power clean.     

Reliability of the one-repetition-maximum power clean test in adolescent athletes

Although the power clean test is routinely used to assess strength and power performance in adult athletes, the reliability of this measure in younger populations has not been examined. Therefore, the purpose of this study was to determine the reliability of the 1-repetition maximum (1RM) power clean in adolescent athletes. Thirty-six male athletes (age 15.9 ± 1.1 years, body mass 79.1 ± 20.3 kg, height 175.1 ±7.4 cm) who had >1 year of training experience in weightlifting exercises performed a 1RM power clean on 2 nonconsecutive days in the afternoon following standardized procedures. All test procedures were supervised by a senior level weightlifting coach and consisted of a systematic progression in test load until the maximum resistance that could be lifted for 1 repetition using proper exercise technique was determined. Data were analyzed using an intraclass correlation coefficient (ICC[2,k]), Pearson correlation coefficient (r), repeated measures analysis of variance, Bland-Altman plot, and typical error analyses. Analysis of the data revealed that the test measures were highly reliable demonstrating a test-retest ICC of 0.98 (95% confidence interval = 0.96-0.99). Testing also demonstrated a strong relationship between 1RM measures in trials 1 and 2 (r = 0.98, p < 0.0001) with no significant difference in power clean performance between trials (70.6 ± 19.8 vs. 69.8 ± 19.8 kg). Bland-Altman plots confirmed no systematic shift in 1RM between trials 1 and 2. The typical error to be expected between 1RM power clean trials is 2.9 kg, and a change of at least 8.0 kg is indicated to determine a real change in lifting performance between tests in young lifters. No injuries occurred during the study period, and the testing protocol was well tolerated by all the subjects. These findings indicate that 1RM power clean testing has a high degree of reproducibility in trained male adolescent athletes when standardized testing procedures are followed and qualified instruction is present.     

Functional patterns and temperature response of cellulose-fermenting microbial cultures containing different methanogenic communities

The effect of microbial composition on the methanogenic degradation of cellulose was studied using two lines of anaerobic cellulose-fermenting methanogenic microbial cultures at two different temperatures: that at 15 degrees C being dominated by Methanosaeta and that at 30 degrees C by Methanosarcina. In both cultures, CH4 production and acetate consumption were completely inhibited by either 2-bromoethanesulfonate or chloroform, whereas H2 consumption was only inhibited by chloroform, suggesting that homoacetogens utilized H2 concomitantly with methanogens. Hydrogen was the intermediate that was consumed first, while acetate continued to accumulate. At 15 degrees C, acetoclastic methanogenesis smoothly followed H2-dependent CH4 production. Fluorescence in situ hybridization showed that populations of Methanosaeta steadily increased with time from 5 to 25% of total cell counts. At 30 degrees C, two phases of CH4 production were obtained, with acetate consumed after the abrupt increase of Methanosarcina from 0 to 45% of total cell counts. Whereas populations of Methanosaeta were able to adapt after transfer from 15 to 30 degrees C, those of Methanosarcina were not, irrespective of during which phase the cultures were transferred from 30 degrees C to 15 degrees C. Our results thus show that the community structure of methanogens indeed affects the function of a cellulose-fermenting community with respect to temperature response.     

Lactate dehydrogenase isoenzyme study of Trichinella larvae of different ages

LDH isoenzymes of Trichinella larvae isolated from experimentally infected guinea pigs were investigated between days 30 and 400 inclusive after infection. It was found that on the 30 th day after infection the larvae have two isoenzymes while from the 40th to the 400 th day--three isoenzymes. The first of the latter is of fast responce and is located in the anod area near the indicator while the two others are of slow response and are located between the isoenzymes LDH-3 and LDH-5 of the muscular tissue of guinea pigs. This indicates that energetic metabolism of Trichinella larvae proceeds in muscular tissues by aerobic and anaerobic way. Since electrophoretic specificity of LDH-isoenzymes of Trichinella larvae differ from that of LDH-isoenzymes of muscular tissue the former are apparently characteristic of Trichinella larvae.     

Lactate dehydrogenase isoenzyme patterns as a method of pregnancy detection in cattle

The objective of this study was to evaluate serum lactate dehydrogenase isoenzyme patterns in open and pregnant Holstein and Hereford cows as a method of detecting pregnancy. Serum samples were collected from 26 Holstein and 13 Hereford cows and lactate dehydrogenase isoenzyme patterns were examined by electrophoresis and quantitated by scanning densitometry. Lactate dehydrogenase isoenzyme(4) and LDH(5) were found in higher concentration (P 相似文献   

The effect that side dominance has on barbell power symmetry during the hang power clean

The aim of this study was to examine whether ground reaction force (GRF) side differences were transmitted and related to bar end power output asymmetries during hang power clean (HPC) performance and whether progressive loading would intensify this effect. Differences between the dominant (D) and nondominant (ND) side average GRFs (AGRFs) of both feet and average bar end power outputs were recorded simultaneously from 15 recreationally trained male volunteers at 30, 60, and 90% 1RM using 2 force platforms and 3 high-speed digital cameras, quantifying side dominance from perceived handedness (left- or right-side dominance [LRSD]), GRF side dominance (force side dominance [FSD]), and bar end power output side dominance (barbell side dominance [BSD]). With the exception of the LRSD condition, differences between the D and ND side AGRFs were significant (FSD: 1.8-4.3%; BSD: 5.1-6.4%, p < 0.05). Bar end power output side differences were significant for all conditions (LRSD: 1.5-5.4%; FSD: 0.5-3.4%; BSD: 3.9-5.6%, p < 0.05). Progressive loading did not significantly affect GRF side differences or the FSD average bar power side differences. However, during the LRSD and BSD conditions, the 60 and 90% side average bar power side differences were >the 30% equivalents. Average GRF side differences were not related to bar end power output side differences. Because of the consistent side difference of 4-6% investigators and strength and conditioning practitioners should exercise caution when interpreting changes in bar end power output.