Igor Štirn

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

Abstract 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.

Relationship between different push-off variables and start performance in experienced swimmers

Abstract The objective of this study was to determine the relationship between different variables measured with a force plate during the swimming start push-off phase and start performance presented by times to 5, 10 and 15 m. Twenty-one women from the Slovenian national swimming team performed two different swim starts (freestyle and undulatory) on a portable force plate to a distance further than 15 m. Correlations between push-off variables and times to 5, 10 and 15 m were quantified through Pearsons product-moment correlation coefficient (r). The variables that significantly correlated (p < .05) to all times measured in the two starts performed were: average horizontal acceleration (freestyle: r = −0.58 to −0.71; and undulatory: r = −0.55 to −0.66), horizontal take-off velocity (freestyle: r = −0.56 to −0.69; and undulatory: r = −0.53 to −0.67) and resultant take-off velocity (freestyle: r = −0.53 to −0.65; and undulatory: r = −0.52 to −0.61). None of the variables derived from the vertical force were correlated to swimming start performance (p > .05). Based on the results of this study, we can conclude that horizontal take-off velocity and average horizontal acceleration (calculated as the average horizontal force divided by swimmers body mass) are the variables most related to swimming start performance in experienced swimmers, and therefore could be the preferred measures to monitor swimmers’ efficiency during the push-off phase.

The maximal mechanical capabilities of leg extensors muscles to generate velocity and power improve at altitude.

Abstract García-Ramos, A, Štirn, I, Padial, P, Argüelles-Cienfuegos, J, De la Fuente, B, Strojnik, V, and Feriche, B. The maximal mechanical capabilities of leg extensors muscles to generate velocity and power improve at altitude. J Strength Cond Res 32(2): 475–481, 2018—This study aimed (a) to analyze the effect of an acute exposure to terrestrial altitude on the force-velocity relationship parameters (maximum force [F0], maximum velocity [V0], and maximum power [P0]) during a loaded squat jump (SJ), and (b) to compare unloaded SJ and countermovement jump (CMJ) performance between sea level and altitude conditions. Seventeen international swimmers were tested at sea level (295 m asl) and 7 days later at terrestrial altitude (2,320 m asl) during their first 24 hours of altitude exposure. The maximum values of force and velocity were recorded during a loaded SJ (25–100% of body weight) to determine F0, V0, and P0 parameters. Inconsequential differences between environmental conditions were found for F0 (p = 0.993, 0.02%). However, V0 (p = 0.038, 7.6%) and P0 (p = 0.004, 6.8%) were higher at altitude. Peak values of force (SJ: p = 0.420, 1.19%; CMJ: p = 0.010, 3.6%), power (SJ: p = 0.028, 3.5%; CMJ: p = 0.005, 3.82%), and take-off velocity (SJ: p = 0.071, 1.6%; CMJ: p = 0.009, 1.9%) recorded during the SJ and CMJ were also higher at altitude. These results highlight the potential effect of an acute exposure to terrestrial altitude on enhancing vertical jump performance. The increase in maximal power of the leg muscles at altitude is caused by an improvement in the theoretical maximal velocity at which lower limbs can extend with no significant changes in the theoretical maximal force.

The Effect of an Altitude Training Camp on Swimming Start Time and Loaded Squat Jump Performance

This study evaluated the influence of an altitude training (AT) camp on swimming start time and loaded squat jump performance. To accomplish this goal, 13 international swimmers (8 women, 5 men) were allocated to both the control (Sea Level Training, SLT) and experimental conditions (AT, 2320 m above sea level) that were separated by a one year period. All tests (15 m freestyle swimming start and loaded squat jumps with additional loads of 25%, 50%, 75%, and 100% of swimmers’ body weight) were performed before and after a concurrent 3-week strength and endurance training program prescribed by the national coach. Following the SLT camp, significant impairments in swimming start times to 10 (+3.1%) and 15 m (+4.0%) were observed (P < 0.05), whereas no significant changes for the same distances were detected following the AT camp (-0.89%; P > 0.05). Trivial changes in peak velocity were obtained during the loaded squat jump after both training periods (effect sizes: < 0.20). Based on these results we can conclude that a traditional training high—living high strategy concurrent training of 3 weeks does not adversely affect swimming start time and loaded squat jump performance in high level swimmers, but further studies are necessary to assess the effectiveness of power-oriented resistance training in the development of explosive actions.

Reliability Analysis of Traditional and Ballistic Bench Press Exercises at Different Loads.

Abstract The purpose of this study was to determine test–retest reliability for peak barbell velocity (Vpeak) during the bench press (BP) and bench press throw (BPT) exercises for loads corresponding to 20–70% of one-repetition maximum (1RM). Thirty physically active collegiate men conducted four evaluations after a preliminary BP 1RM determination (1RM·bw-1 = 1.02 ± 0.16 kg·kg-1). In counterbalanced order, participants performed two sessions of the BP in one week and two sessions of the BPT in another week. Recovery time between sessions within the same week was 48 hours and recovery time between sessions of different weeks was 120 hours. On each day of evaluation the individual load-velocity relationship at each tenth percentile (20–70% of 1RM) in a Smith machine for the BP or BPT was determined. Participants performed three attempts per load, but only the best repetition (highest Vpeak), registered by a linear position transducer, was analysed. The BPT resulted in a significantly lower coefficient of variation (CV) for the whole load–velocity relationship, compared to the BP (2.48% vs. 3.22%; p = 0.040). Test–retest intraclass correlation coefficients (ICCs) ranged from r = 0.94-0.85 for the BPT and r = 0.91-0.71 for the BP (p < 0.001). The reduction in the biological within-subject variation in BPT exercise could be promoted by the braking phase that obligatorily occurs during a BP executed with light or moderate loads. Therefore, we recommend the BPT exercise for a most accurate assessment of upper-body velocity.

The Relationship Between the Lower-Body Muscular Profile and Swimming Start Performance

Abstract This study aimed to examine the correlation of different dry land strength and power tests with swimming start performance. Twenty international level female swimmers (age 15.3 ± 1.6 years, FINA point score 709.6 ± 71.1) performed the track freestyle start. Additionally, dry land tests were conducted: a) squat (SJ) and countermovement jumps (CMJ), b) squat jumps with additional resistance equivalent to 25, 50, 75 and 100% of swimmers’ body weight [BW]), and c) leg extension and leg flexion maximal voluntary isometric contractions. Correlations between dry land tests and start times at 5, 10 and 15 m were quantified through Pearson’s linear correlation coefficients (r). The peak bar velocity reached during the jumps with additional resistance was the variable most correlated to swimming start performance (r = -0.57 to -0.66 at 25%BW; r = -0.57 to -0.72 at 50%BW; r = -0.59 to -0.68 at 75%BW; r = -0.50 to - 0.64 at 100%BW). A few significant correlations between the parameters of the SJ and the CMJ with times of 5 and 10 m were found, and none with the isometric variables. The peak velocity reached during jumps with external loads relative to BW was found a good indicator of swimming start performance.

Frequent Immediate Knowledge of Results Enhances the Increase of Throwing Velocity in Overarm Handball Performance

Abstract In the present study, the effect of frequent, immediate, augmented feedback on the increase of throwing velocity was investigated. An increase of throwing velocity of a handball set shot when knowledge of results was provided or not provided during training was compared. Fifty female and seventy-three male physical education students were assigned randomly to the experimental or control group. All participants performed two series of ten set shots with maximal effort twice a week for six weeks. The experimental group received information regarding throwing velocity measured by a radar gun immediately after every shot, whereas the control group did not receive any feedback. Measurements of maximal throwing velocity of an ordinary handball and a heavy ball were performed, before and after the training period and compared. Participants who received feedback on results attained almost a four times greater relative increase of the velocity of the normal ball (size 2) as compared to the same intervention when feedback was not provided (8.1 ± 3.6 vs. 2.7 ± 2.9%). The velocity increases were smaller, but still significant between the groups for throws using the heavy ball (5.1 ± 4.2 and 2.5 ± 5.8 for the experimental and control group, respectively). Apart from the experimental group throwing the normal ball, no differences in velocity change for gender were obtained. The results confirmed that training oriented towards an increase in throwing velocity became significantly more effective when frequent knowledge of results was provided.

The examination of different tests for the evaluation of the efficiency of the eggbeater kicks.

Abstract The eggbeater kick presents an important basic technical skill in water polo. The aim of this study was to examine some different tests in order to recommend the best ones for the evaluation of the eggbeater kick. Twenty eight young male water polo players performed one test (squat jump) on land and ten tests in water: tethered swimming with legs only, using alternating and simultaneous eggbeater kicks, jumps out of water from basic and vertical (arms vertically above the head) position, water start and swimming two meters and swimming horizontally with legs only five meters with a flying start. The differences between tests were checked by executing dependent t-tests, while Pearsons correlation coefficients were calculated to evaluate the correlation between different parameters. Results showed that when performing alternate eggbeater kicks greater average forces were produced by the water polo players when compared to consecutive simultaneous eggbeater kicks. However, a short time maximal acceleration of the body in the vertical and horizontal plane was greater when the single simultaneous kick was performed. It was determined that horizontal swimming using legs only and a squat jump were less useful for the evaluation of the eggbeater kick. Therefore, the recommendation was to measure the average force of successive alternating eggbeater kicks, the height of the jump out of the water from the basic position and the water start and swim over a distance of 2 meters.

Evaluation of mean power spectral frequency of EMG signal during 100 metre crawl

Abstract The aim of our study was to compare mean frequency (MNF) decrease in some upper body muscles during a 100-metre all-out crawl by using two different normalization methods: firstly, when MNF at the end of swimming (MNFSend) was normalized with respect to its initial value at the beginning and expressed with a fatigue index (FI) labelled FIstart, and secondly when MNFmin was used to calculate FImin. MNFmin presented the lowest MNF obtained during isometric contractions until exhaustion executed on land after swimming for each of three observed muscles – triceps brachii (TB), latissimus dorsi (LD) and pectoralis major (PM). Eleven experienced swimmers participated in the study and surface electromyography (EMG) signals from TB, the upper and lower parts of LD (LD1 and LD2 respectively) and the upper and lower parts of PM (PM1 and PM2 respectively) were recorded during both swimming and isometric contractions. Results showed no differences in FIstart; however, when FImin values were compared differences between the muscles were found (P<0.05). The triceps brachii (TB) and the upper part of the latissimus dorsi muscles (LD1) showed the lowest FImin (40.0±15.7 and 40.7±24.4 respectively), which implied that MNFSend obtained from these muscles most closely approached their respective MNFmin values during swimming. This might suggest that these muscles fatigued more than other observed muscles. The use of a different type of muscle contraction for calculating FImin (isometric versus dynamic) might represent a drawback to our study, but this approach could be acceptable when between-muscle comparisons are made.

Comparison of lower leg muscle activity in running on tarmac and grass

The observation that dynamic ankle DF is not predicted by passive ankle DF is consistent with previous observations of low correlation between static and dynamic measures (Hamill et al. 1989). This highlights the importance of measuring ankle DF during dynamic running gait if seeking to identify those with limited functional ankle DF. Through measurement of dynamic ankle DF during running, it has been possible to identify those recruits will low functional DF. The additional measurement of plantar pressures has revealed that limited dynamic ankle DF does not necessarily lead to high MT3 loading. The low correlations between peak ankle DF in running and the magnitude of load, represented by peak force, loading rate or impulse, suggests that factors other than ankle DF are important in determining the load on this area. This finding is consistent with that of Sacco et al. (2001), investigating walking, and highlights the importance of measuring forefoot loading directly, rather than inferring load from kinematic measurements of DF.