Effect of Different Types of Loads on the Force-Velocity Relationship Obtained During the Bench Press Throw Exercise.

ABSTRACT: Cosic, M, Knezevic, OM, Nedeljkovic, A, Djuric, S, Zivkovic, MZ, and Garcia-Ramos, A. Effect of different types of loads on the force-velocity relationship obtained during the bench press throw exercise. J Strength Cond Res 35(9): 2401-2406, 2021-This study aimed (a) to evaluate the degree of linearity of the force-velocity (F-V) relationship across different types of loads, (b) to compare the magnitude of the F-V relationship parameters (maximum values of force [F0], velocity [V0], and power [Pmax]) between the different types of loads, and (c) to explore the concurrent validity of F0 with traditional measures of maximal strength. The F-V relationships of 15 physically active men (age: 20.9 ± 2.0 years, bench press 1 repetition maximum relative to body mass: 1.20 ± 0.10 kg·kg-1) were determined during the bench press throw exercise using predominantly gravitational (W), inertial (I), and combined (W + I) loads. The bench press maximal isometric force (Fiso) and the 1RM were also assessed. The individual F-V relationships were highly linear regardless of the type of load considered (median r [range] = 0.98 [0.94, 1.00]). The W + I load provided the largest value of F0 (972 ± 45 N; 6.0 and 14.6% higher than W and I, respectively), the I load the largest value of V0 (2.99 ± 0.34 m·s-1; 40.4 and 20.1% higher than W and W + I, respectively), and the W load the lowest value of Pmax (501 ± 46 W; -22.7 and -17.1% lower than I and W + I, respectively). The F0 obtained from the W load presented the highest association with Fiso and 1RM values (r > 0.90). The W + I load and the I load should be recommended to work closer to the F0 and V0 capacities, respectively. However, the W load should be recommended to assess maximal strength capacity through the value of F0.

Seasonal variations of Saanen goat milk composition and the impact of climatic conditions.

The aim of this research was to investigate the effect of climatic conditions and their impact on seasonal variations of physico-chemical characteristics of Saanen goat milk produced over a period of 4 years. Lactation period (early, mid and late) and year were considered as factors that influence physico-chemical composition of milk. Pearson's coefficient of correlation was calculated between the physico-chemical characteristics of milk (fat, proteins, lactose, non-fat dry matter, density, freezing point, pH, titrable acidity) and climatic condition parameters (air temperature, temperature humidity index-THI, solar radiation duration, relative humidity). Results showed that all physico-chemical characteristics of Saanen goat milk varied significantly throughout the lactation period and years. The decrease of fat, protein, non-fat dry matter and lactose content in goat milk during the mid-lactation period was more pronounced than was previously reported in the literature. The highest values for these characteristics were recorded in the late lactation period. Observed variations were explained by negative correlation between THI and the physico-chemical characteristics of Saanen goat milk. This indicated that Saanen goats were very prone to heat stress, which implied the decrease of physico-chemical characteristics during hot summers.

A Novel Two-Velocity Method for Elaborate Isokinetic Testing of Knee Extensors.

Single outcomes of standard isokinetic dynamometry tests do not discern between various muscle mechanical capacities. In this study, we aimed to (1) evaluate the shape and strength of the force-velocity relationship of knee extensors, as observed in isokinetic tests conducted at a wide range of angular velocities, and (2) explore the concurrent validity of a simple 2-velocity method. Thirteen physically active females were tested for both the peak and averaged knee extensor concentric force exerted at the angular velocities of 30°-240°/s recorded in the 90°-170° range of knee extension. The results revealed strong (0.960

Contralateral limb deficit after ACL-reconstruction: an analysis of early and late phase of rate of force development.

The aim of this study was to assess the effect of a unilateral anterior cruciate ligament reconstruction (ACLR) on maximum voluntary contraction (MVC) and explosive strength of both the involved limb and the uninvolved limb. Nineteen male athletes completed a standard isometric testing protocol 4 months post-ACLR, while 16 healthy participants served as a control group (CG). The explosive strength of the knee extensors and flexors was assessed as RFD obtained from the slope of the force-time curves over various time intervals. Both muscle groups of the involved limb had significantly lower MVC compared to the uninvolved. The involved limb also had significantly lower RFD in the late phase of contraction (140-250 ms) for both knee extensors and flexors (P < 0.05). There was no difference in MVC between the uninvolved limb and the CG. However, RFD of the uninvolved limb was lower compared to CG for both knee extensors (0-180 ms; P < 0.01) and flexors (0-150 ms; P < 0.05). ACLR leads to lower MVC and explosive strength of the involved limb. As a consequence of potential crossover (presumably neural-mediated) effects, explosive strength deficits could be bilateral, particularly in the early phase of the contraction (<100 ms).

Evaluation of force-velocity and power-velocity relationship of arm muscles.

PURPOSE: A number of recent studies have revealed an approximately linear force-velocity (F-V) and, consequently, a parabolic power-velocity (P-V) relationship of multi-joint tasks. However, the measurement characteristics of their parameters have been neglected, particularly those regarding arm muscles, which could be a problem for using the linear F-V model in both research and routine testing. Therefore, the aims of the present study were to evaluate the strength, shape, reliability, and concurrent validity of the F-V relationship of arm muscles. METHODS: Twelve healthy participants performed maximum bench press throws against loads ranging from 20 to 70 % of their maximum strength, and linear regression model was applied on the obtained range of F and V data. One-repetition maximum bench press and medicine ball throw tests were also conducted. RESULTS: The observed individual F-V relationships were exceptionally strong (r = 0.96-0.99; all P < 0.05) and fairly linear, although it remains unresolved whether a polynomial fit could provide even stronger relationships. The reliability of parameters obtained from the linear F-V regressions proved to be mainly high (ICC > 0.80), while their concurrent validity regarding directly measured F, P, and V ranged from high (for maximum F) to medium-to-low (for maximum P and V). CONCLUSIONS: The findings add to the evidence that the linear F-V and, consequently, parabolic P-V models could be used to study the mechanical properties of muscular systems, as well as to design a relatively simple, reliable, and ecologically valid routine test of the muscle ability of force, power, and velocity production.

Force-velocity relationship of leg extensors obtained from loaded and unloaded vertical jumps.

PURPOSE: Resent research has suggested that loaded multi-joint movements could reveal a linear force-velocity (F-V) relationship. The aim of the present study was to evaluate the F-V relationship both across different types of vertical jumps and across different F and V variables. METHODS: Ten healthy subjects performed maximum various vertical jumps that were either loaded or unloaded by constant external forces of up to 30 % of their body weight. Both the maximum and averaged F and V data were recorded. RESULTS: The observed F-V relationships proved to be strong (median correlation coefficients ranged 0.78-0.93) and quasi-linear. Their F- and V-intercepts and the calculated maximum power (P) were highly reliable (0.85 < ICC < 0.98), while their concurrent validity with respect to their directly measured values was on average moderate-to-large. The obtained F-V relationships also revealed that (1) the assessment of maximum F and P could be somewhat more reliable and valid than the assessment of maximum V, (2) natural countermovement jumps should be employed rather than the jumps performed from a fixed squat position, while (3) both maximum and averaged F and V variables could be used despite revealing markedly different regression parameters. CONCLUSIONS: The data generally reveal a reliable, valid, strong and quasi-linear F-V relationship across variety of vertical jumps and the recorded F and V variables. Therefore, we conclude that the loaded vertical jumps could be developed into a routine method for testing the force, velocity, and power generating capacity of leg extensors.

Power output in vertical jumps: does optimum loading depend on activity profiles?

The previously proposed maximum dynamic output hypothesis (MDO: i.e. the optimum load for maximizing the power output during jumping is one's own body) was tested on individuals of various activity profiles. Forty males (10 strength-trained athletes, 10 speed-trained athletes, 10 physically active non-athletes, and 10 sedentary individuals) performed different vertical jumps on a force plate while a pulley system was used to either reduce or increase the subject's body weight by 10-30 %. As expected, an increase in external loading resulted in a significant increase (p < 0.001) in force output and a concomitant decrease of peak jumping velocity in all groups of participants. The main finding, however, was that all groups revealed the maximum peak and mean power output at approximately the subjects' own body weight although their weight represented prominently different percentage of their maximum dynamic strength. While a significant (p < 0.05), albeit moderate, 'group × load' interaction in one jump was observed for the peak power output, the individual optimum load for maximizing the power output number did not differ among the groups. Although apparently further research on various types of movements is needed, the present results provide, so far, the strongest support of the MDO hypothesis.

Effects of Different Loading Types on the Validity and Magnitude of Force-Velocity Relationship Parameters.

BACKGROUND: Force-velocity (F-V) relationship models gained popularity as a tool for muscle mechanical assessment. However, it is not clear whether the validity of the F-V relationship parameters (maximal theoretical force [F0], velocity [V0] and power [Pmax]) is affected using different load types: gravitational (W, rubber bands pulling the barbell downward), inertial (I, rubber bands pulling the barbell, which is equalized to the weight of the added plates upward), and combined (W + I, weight of the plates). HYPOTHESIS: Load type would affect both the magnitude and validity of F-V relationship parameters. The highest magnitude and validity was expected for F0 using a W, for V0 using an I, and for Pmax using a W + I load. STUDY DESIGN: Cross-sectional. LEVEL OF EVIDENCE: Level 3. METHODS: A total of 13 resistance-trained men (body mass, 87.7 ± 11.2 kg and body height, 183.9 ± 6.4 cm) performed bench press (BP) throws (BPTs) using 3 types of loads against 30 to 80 kg. The validity of F-V relationship parameters was explored with respect to the tests used traditionally for force (maximal voluntary contraction and 1-repetition maximum [1RM]), velocity (maximal velocity achieved during almost unloaded tasks), and power (BPT against the 50%1RM and medicine ball throws) assessment. RESULTS: The W + I loading promoted the highest values of F0 and Pmax, while the highest magnitude of V0 was promoted by the I loading. The validity was acceptable for F0 obtained using the 3 loading conditions with respect to the BP 1RM (r range, 0.30-0.83), and V0 obtained using the I loading with respect to the stick throw (r = 0.54). CONCLUSION: The magnitude of the F-V relationship parameters is affected by load type, but their validity with respect to standardized tests is comparable, with the exception of the higher validity of V0 when obtained using the I loading. CLINICAL RELEVANCE: Any load type can be used for assessing F0, while I load should be selected when assessing V0.

Optimum loading for maximizing muscle power output: the effect of training history.

Although the effect of external load on the mechanical output of individual muscle has been well documented, the literature still provides conflicting evidence regarding whether the optimum loading (L(opt)) for exerting the maximum muscle power output (MPO) could be different for individuals with different levels of strength and power. The aim of this study was to explore the effect of training history on L(opt) that maximizes MPO during the 6-s maximal cycling sprint test. Forty healthy young males (strength-and speed-trained athletes, and physically active and sedentary non-athletes) were tested on maximum strength, and on peak MPO when loaded 5-12% of body weight (BW). As expected, the strength trained and sedentary participants, respectively, revealed the highest and lowest strengths and MPO (p < 0.001). However, the main finding was a significant across-group difference in L(opt) (p < 0.001) revealing the values 9.7% (for strength trained), 9.2% (speed trained), 8.7% (active), and 8.0% of BW (sedentary individuals). This suggests that the effects of external loading on maximum MPO in complex functional movements could be training history dependent. In addition to revealing a sensitivity of the 6-s maximal cycling sprint tests (and, perhaps, other maximum cycling tests), the results suggest that the external loading in routine MPO tests should not be solely adjusted to a fixed percentage of subject's BW (as routinely done in standard tests), but also to their training history. The same phenomenon remains to be evaluated in a number of other routine tests of MPO and other maximum performance tasks.

Alternating consecutive maximum contractions as a test of muscle function.

Although regularly used, the standard strength test (SST) is known to have several shortcomings, such as being based only on sustained maximum forces, and on a relatively large number of trials that expose the tested muscle to rapid fatigue. The purpose of this study was to evaluate alternating consecutive maximum contractions (ACMCs) as a test of the muscle function through its comparison with SST. Twenty-four participants performed both the externally paced isometric ACMC (i.e., series of consecutive maximum force exertions in 2 directions) and SST of the knee extensor and flexor muscle. The derived variables of both tests included the knee extensor and flexor peak forces (PFs) and their maximum rates of development. Movement speed and muscle power output were also assessed through standard maximum performance tests. Both ACMC and SST revealed on average high intratrial (intraclass correlation coefficient [ICC] > 0.80) and moderate-to-high test-retest reliability (ICC > 0.60), and significant (p < 0.05) positive relationships among the PFs and their rates of development of the tested muscles. The variables of both tests also suggested on average moderate correlations with the maximum performance tests. Finally, ACMC variables revealed relatively stable values across a wide range of frequencies including the 'self-selected' one. Although some properties of ACMC could be similar to SST, the important comparative advantages of ACMC could be relatively low and transitional maximum forces exerted, and fewer trials needed for testing 2 antagonistic muscles. Although further research is needed, particularly concerning the external validity and generalizability, we conclude that the ACMC represents a test of muscle function that could be applied either as an alternative or complementary test to SST.

Reliability and Sensitivity of Reaction Time Measurements During Quasi-Realistic Soccer Situations.

Reliability and sensitivity of reaction time (RT) during quasi-realistic soccer situations was explored in 10 professional soccer players (skilled; age = 20.9 ± 3.6 years) and 10 males without soccer experience (nonskilled; age = 23.4 ± 0.5 years). The participants were instructed to react as fast as possible to a stimulus presented via the video-based method while standing on force platforms. RT was computed as the difference between the instant when the rate of force development of any leg reaches 5% of its maximal value and the instant of stimulus presentation. The results revealed acceptable to high reliability of RT (intraclass correlation coefficient median = .90; coefficient of variation ≤ 5.83%), and shorter RT for skilled compared with nonskilled participants in three out of eight comparisons (effect size range = 1.00-1.41). The video-based methods can be confidently used to assess the RT in soccer players.

Effects of Resistance Training With Constant, Inertial, and Combined Loads on Muscle Power and Strength Output.

The aim of this study was to investigate the resistance-specific gains in muscle power and strength (1RM) following the training of maximum bench-press throws (BPT) against constant, inertial, and combined resistance. Forty-eight male participants (age 20.5 ± 2.0 years) were randomly assigned to the constant, inertial, combined resistance, or control group. Participants underwent 8 weeks of training of BPT against the loads that corresponded to the different effects of mass of 40 kg (∼50% of 1RM). The gains in average and maximum power, and 1RM were significant in all experimental groups (P < 0.01), but not in the control group (P > 0.1). Relative gains in the average (26.3 ± 9.8%) and maximum power (25.2 ± 9.8%) were larger than that in the 1RM (mean 7.2 ± 6.9%; both P < 0.001). The gains in the average (F 4, 66 = 6.0; P < 0.01) and maximum power (F 4, 66 = 4.7; P < 0.01) were higher when tested against the training-specific resistance than when tested against the remaining two resistance types. Differences in 1RM among experimental groups were not significant (P = 0.092). The most important and rather novel finding of the study is that the training against the weight and inertial resistance, and their combination results in resistance-specific gains in muscle power, although the overall gains muscle strength and power remain comparable across the training protocols.

Optimal Instructions to Maximize Attack Efficiency in Beginners and Experienced Fencers.

This study aimed to determine the instruction that maximizes fencing attack performance and to explore the sensitivity of a novel efficiency index (EI) that considers reaction time, attack velocity, and absolute error to discriminate between beginners and experienced fencers. Instructions that directed attentional focus internally (react as fast as possible and perform the attack movement as fast as possible) or externally (be as accurate as possible) were provided prior to stimulus presentation. The EI did not differ between the instructions in any group (p > .05), the instructions "react as fast as possible" and "be as accurate as possible" promoted in beginners the highest and the lowest EI, and the EI was higher for fencers. Our findings suggest that the EI could be recommended as a general index of fencing attack efficiency.

Comparison of reaction time between beginners and experienced fencers during quasi-realistic fencing situations.

This study aimed (I) to investigate the impact of the number of stimulus-responses alternatives on reaction time (RT) under quasi-realistic fencing situations, and (II) to elucidate whether the regression slope based on the RT and the number of stimulus-responses alternatives could distinguish between beginners and experienced fencers. Ten beginners (7 men) and 10 experienced (6 men) fencers participated in the study. A video-based method was used to present four typical fencing movement techniques (i.e. "stimulus") after which the participants had to perform an offensive (high or low attack) or defensive (high or low defence) action (i.e. "response"). The simple-RT (specific stimulus known in advance), 2Choice-RT (only defensive or offensive stimuli), and 4Choice-RT (all possible stimuli) were evaluated. The increase in the number of stimulus-responses alternatives was associated with higher RT (4Choice-RT > 2Choice-RT > Simple-RT; p < 0.05). Beginners always presented higher RT compared to fencers (range: 25.5-34.8%; p < 0.05) and also showed a steeper slope of the relationship between RT and the number of stimulus-responses alternatives (range: 35.2-55.2%; p < 0.05). These results suggest that the capability to quickly respond to specific fencing stimuli increases with training experience, being the differences accentuated with increasing number of stimulus-responses alternatives.

Tests of muscle power output assess rapid movement performance when normalized for body size.

Among other routinely tested physical abilities, the tests of rapid movement performance and the tests of direct assessment of muscle power have been independently evaluated in complex batteries of physical fitness tests. Based on the scaling effects, we hypothesized that the tests of rapid movement performance assess the same physical ability as the tests of direct assessment of muscle power properly normalized for the effect of body size. Young physically active men (n = 111) were evaluated on 23 physical ability tests based on the assessment of muscle strength, muscle power, and rapid movement performance. When non-normalized data were used, a principle component analysis revealed a structure with overlapping tests from the above-mentioned groups including the indices of body size. However, when the indices of muscle strength and directly assessed muscle power were properly normalized for the effect of body size, the obtained structure was in line with the hypothesis. Most of the tests of both the direct assessment of muscle power and rapid movement performance proved to belong to the same factor, whereas the muscle strength tests and body size measures, respectively, loaded the remaining 2 factors. This result suggests that the rapid movement performance could be employed to assess muscle power and, possibly, the neuromuscular efficiency in general, which could be important for understanding some basic aspects of the design and function of the human locomotor system. An important practical implication of our findings could be that the direct assessment of muscle power (that usually requires expensive equipment and complex data processing procedures) could be skipped from the complex batteries of physical fitness tests and replaced by generally simpler tests of rapid movement performance.

Is Test Standardization Important when Arm and Leg Muscle Mechanical Properties are Assessed through the Force-Velocity Relationship?

The force-velocity (F-V) relationship observed in multi-joint tasks proved to be strong and approximately linear. Recent studies showed that mechanical properties of muscles: force (F), velocity (V) and power (P) could be assessed through the F-V relationship although the testing methods have not been standardized. The aim of the present study was to evaluate and compare F-V relationships assessed from two tests performed on a modified Smith machine that standardizes kinematics of the movement pattern. Fifteen participants were tested on the maximum performance bench press throws and squat jumps performed against a variety of different loads. In addition, their strength properties were assessed through maximum isometric force (Fiso) and one repetition maximum (1 RM). The observed individual F-V relationships were exceptionally strong and approximately linear (r = 0.98 for bench press throws; r = 0.99 for squat jumps). F-V relationship parameter depicting maximum force (F0) revealed high correlations with both Fiso and 1 RM indicating high concurrent validity (p < 0.01). However, the generalizability of F-V relationship parameters depicting maximum force (F0), velocity (V0) and power (P0) of the tested muscle groups was inconsistent and on average low (i.e. F0; r = -0.24) to moderate (i.e. V0 and P0; r = 0.54 and r = 0.64, respectively; both p < 0.05). We concluded that the F-V relationship could be used for the assessment of arm and leg muscle mechanical properties when standard tests are applied, since the typical outcome is an exceptionally strong and linear F-V relationship, as well as high concurrent validity of its parameters. However, muscle mechanical properties could be only partially generalized across different tests and muscles.

Evaluation of the reliability of soccer-specific field tests.

The soccer-specific field tests are popular among coaches due to their simplicity, validity, and minimal use of equipment. Nevertheless, there is a general lack of data about their reliability, particularly regarding the tests of anaerobic performance. Twenty professional male soccer players performed 3 consecutive trials of the tests of throwing-in and standing-kick performance (the distance measured) as well as on timed 10-m sprint, flying 20-m sprint, running 10 x 5 m, zigzag running with and without the ball, and the skill index (i.e., the ratio of the zigzag running without and with the ball). With the exception of the throwing-in and standing kick, the evaluated tests revealed high intraclass correlation coefficients (i.e., >0.80), small within-individual variations (coefficient of variation, <4%), and sample sizes for detecting a 2% change in the tested performance that are either close to or below the standard size of a professional soccer squad. In addition to simplicity and face validity, most of the evaluated tests revealed high reliability. Therefore, the evaluated tests are recommended for sport-specific profiling and early selection of young athletes as well as for routine testing procedures that could detect effects of various intervention procedures. Regarding the throwing-in and standing-kick tests, direct measurement of the ball velocity (e.g., with a standard radar gun) is recommended.

Feasibility of discrimination of dairy creams and cream-like analogues using Raman spectroscopy and chemometric analysis.

Dairy cream and its analogues with sunflower oil, coconut oil and palm oil in different milk fat/vegetable fat ratios were prepared and analysed using Raman spectroscopy. The linear discriminant analysis was conducted in order to classify the samples. Samples were well separated and displayed distinguishing linear arrangement along the principal component that expressed the variation in lipid unsaturation. Good separation of sunflower oil and milk fat samples was obtained in contrast to the samples with coconut and palm oil, where the substantial overlapping occurred. The method permitted classifying of the samples in terms of the type of fat used. Calibrated model was extremely sensitive (100%) for dairy cream. The results indicated that it is possible to consider the Raman spectroscopy coupled with chemometric analysis as a rapid way for the detection of dairy cream adulteration with sunflower, coconut and palm oils.

Force-velocity property of leg muscles in individuals of different level of physical fitness.

The present study explored the method of testing muscle mechanical properties through the linear force-velocity (F-V) relationships obtained from loaded vertical jumps. Specifically, we hypothesised that the F-V relationship parameters depicting the force, power, and velocity of the tested muscles will differ among individuals of different physical fitness. Strength trained, physically active, and sedentary male participants (N = 10 + 10 + 10; age 20-29 years) were tested on maximum countermovement and squat jumps where manipulation of external loads provided a range of F and V data. The observed F-V relationships of the tested leg muscles were approximately linear and mainly strong (median correlation coefficients ranged from 0.77 to 0.92; all p < 0.05), independently of either the tested group or the jump type. The maximum power revealed higher values in the strength trained than in the physically active and sedentary participants. This difference originated from the differences in F-intercepts, rather than from the V-intercepts. We conclude that the observed parameters could be sensitive enough to detect the differences among both the individuals of different physical fitness and various jump types. The present findings support using loaded vertical jumps and, possibly, other maximum performance multi-joint movements for the assessment of mechanical properties of active muscles.