The purpose of the study was to determine the acute responses to a jump squat protocol designed to induce postactivation potentiation on sprint running performance in experienced track and field athletes and soccer players. Twenty-five regional level athletes (12 track and field: ∼17 years; ∼177 cm; ∼73 kg and 13 soccer: ∼18 years; ∼175 cm; ∼72 kg) performed 2 test sessions assessing 40-m sprint running performance in a balanced, crossover design. Dual-beam light timing gates measured 0-20 and 20-40 m sprint times before and after either 9 minutes of sitting (control) or 2 sets of 6 repetition half-squat jump with the load eliciting maximum power (experimental) conditions. Sprint performance was significantly enhanced over both 0-20 m (3.09 ± 0.07 to 3.04 ± 0.08 seconds; Δ ∼1.5%; p ≤ 0.05) and 20-40 m (2.42 ± 0.09 to 2.39 ± 0.09 seconds; Δ ∼1%; p ≤ 0.05) in track and field athletes only. Also, the magnitude of enhanced sprint performance was related to baseline 0-20 m sprint performance (r = 0.44; p = 0.028; n = 25). It seems that using loaded half-squat jumps to enhance sprint performance could be used in training of high-level young athletes.

It has been clearly established that maximal force and power is lower in the morning compared to noon or afternoon hours. This morning neuromuscular deficit can be diminished by regularly training in the morning hours. However, there is limited and contradictory information upon hypertrophic adaptations to time-of-day-specific resistance training. Moreover, no cellular or molecular mechanisms related to muscle hypertrophy adaptation have been studied with this respect. Therefore, the present study examined effects of the time-of-day-specific resistance training on muscle hypertrophy, phosphorylation of selected proteins, hormonal concentrations and neuromuscular performance. Twenty five previously untrained males were randomly divided into a morning group (n = 11, age 23 ± 2 yrs), afternoon group (n = 7, 24 ± 4 yrs) and control group (n = 7, 24 ± 3 yrs). Both the morning and afternoon group underwent hypertrophy-type of resistance training with 22 training sessions over an 11-week period performed between 07:30-08:30 h and 16:00-17:00 h, respectively. Isometric MVC was tested before and immediately after an acute loading exclusively during their training times before and after the training period. Before acute loadings, resting blood samples were drawn and analysed for plasma testosterone and cortisol. At each testing occasion, muscle biopsies from m. vastus lateralis were obtained before and 60 min after the acute loading. Muscle specimens were analysed for muscle fibre cross-sectional areas (CSA) and for phosphorylated p70S6K, rpS6, p38MAPK, Erk1/2, and eEF2. In addition, the right quadriceps femoris was scanned with MRI before and after the training period. The control group underwent the same testing, except for MRI, between 11:00 h and 13:00 h but did not train. Voluntary muscle strength increased significantly in both the morning and afternoon training group by 16.9% and 15.2 %, respectively. Also muscle hypertrophy occurred by 8.8% and 11.9% (MRI, p < 0.001) and at muscle fibre CSA level by 21% and 18% (p < 0.01) in the morning and afternoon group, respectively. No significant changes were found in controls within these parameters. Both pre- and post-training acute loadings induced a significant (p < 0.001) reduction in muscle strength in all groups, not affected by time of day or training. The post-loading phosphorylation of p70S6Thr421/Ser424 increased independent of the time of day in the pre-training condition, whereas it was significantly increased in the morning group only after the training period (p < 0.05). Phosphorylation of rpS6 and p38MAPK increased acutely both before and after training in a time-of-day independent manner (p < 0.05 at all occasions). Phosphorylation of p70S6Thr389, eEF2 and Erk1/2 did not change at any time point. No statistically significant correlations were found between changes in muscle fibre CSA, MRI and cell signalling data. Resting testosterone was not statistically different among groups at any time point. Resting cortisol declined significantly from pre- to post-trai...

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PURPOSE Many types of vertical jumps (VJ) are commonly used to assess the development of the level of explosive strength of lower limbs achieved after a training period. This study is focused on comparing various parameters of different types of VJ with 1 RM in Olympic-style weightlifting, squat and deadlift with an Olympic bar.METHODS Twelve elite weightlifters (men=8; women=4; age 26±4 years, height = 173±8 cm; weight 93±23 kg; weight category from 64 kg to +109 kg) were tested for 1 RM in the following exercises: snatch, clean and jerk, deadlift, squat and variations of VJ on dynamometric plates (Kistler Force Plate). The variations of VJ were: squat jump with the arm swing (SJA) and non-arm swing (SJ), countermovement jump with the arm swing (CMJA) and non-arm swing (CMJ). The parameters compared for each type of VJ were: jump height (m), relative force (% of body weight), relative power (W/kg of body weight) and average power (W). For statistical analysis, the parametric Pearsons correlation coefficient with α=0.05 was used. RESULTS The results show a significant correlation between 1 RM in exercises with an Olympic bar (snatch, clean and jerk, back squat and deadlift) and the CMJ, CMJA, SJ and SJA only in the average power output (W) parameter (p<0.05). The significant correlation coefficients in the average power output (W) were for the CMJA and the snatch r=0.96 r2= 0.92, clean and jerk r=0.96 r2= 0.92, back squat r=0.97 r2= 0.94 and deadlift r=0.93 r2= 0.86; CMJ with hands on the hips and the snatch r=0.93 r2= 0.86, clean and jerk r= 0.93 r2= 0.86, back squat r= 0.95 r2= 0.90 and deadlift r= 0.94 r2= 0.88; for the SJA and the snatch r=0.8 r2= 0.64, clean and jerk r=0.81 r2= 0.65, back squat r=0.82 r2= 0.67 and deadlift r=0.78 r2= 0.60; for the SJ with hands on the hips and the snatch r= 0.76 r2= 0.57, clean and jerk r= 0.75 r2= 0.56, back squat r= 0.77 r2= 0.59 and deadlift r= 0.71 r2= 0.50. Significant correlation coefficients were not found for 1 RM in the snatch, clean and jerk, back squat and deadlift and the CMJ or SJ with and without arm swing in any of the following parameters: jump height (m), relative force (% of body weight), relative power output (W/kg of body weight).CONCLUSION The main finding is that the jump height (m) of the CMJ or SJ with or without arm swing did not correlate significantly with 1 RM in the snatch, clean and jerk, back squat and deadlift. Therefore, jump height measurement can be used as a motivation tool but not to predict maximum strength in Olympic bar exercises, or vice versa. We recommend using the average power output (W) parameter in the CMJ with using arms as a predictor of current performance level in exercises with an Olympic bar for men and women.Key words: snatch, clean and jerk, squat, deadlift, countermovement jump, squat jump

The aim two groups time parallel 6-week experiment was to compare selected types of plyometric training. One group trained with gradation of external weight loading in eccentric phase (EXP1) and the second group increased drop height (EXP2) during drop jump training. We compared their effects on changes in selected strength abilities. We assessed the level of countermovement vertical jump height (CMJ), standing vertical jump height (SJ) and average force gradient in squat exercises with the knee joint in 90 ° by maximal isometric contraction at intervals of 0-50 ms (RFD50) and 0-200 ms (RFD200). The results showed that in CMJ EXP1 had improved by 1.01 cm (3.5%) (p<0.01). EXP2 improved by an average of 1.78 cm (5.5 %) (p<0.05). SJ in EXP1 average improved by 0.94 cm (3.5 %) (p = n.s.) in EXP2 by 1.91 cm (6.6 %) (p<0.05). In RDF50 the average increase observed after a period of training in EXP1 1.03 N.ms-1 (26.08 %) (p = n.s.) and EXP2 0.57 N.ms-1 (16.39 %) (p<0.05). In the EXP1 RFD200 the average increase was 2.51 N.ms-1 after a period of training (20.91 %) (p<0.01), while on average EXP2 improved by 1.05 N.ms-1 (10.04 %) (p = n.s.). Based on these results we recommend to improving of vertical jump height with a countermovement and force gradient in longer intervals (200 ms) to apply the external weight in the form of small dumbbells in eccentric phase of drop jump training. To standing jump height development and shorter time intervals of force gradient (50 ms) is recommended to use a gradual increase in height of drop in plyometric training.

This study investigated the effects of instantaneous performance feedback during the jumpsquat exercise over a 6-week training period. Twenty-five strength-trained athletes were randomly divided into an instant feedback (n = 13, half-squat 3-RM/body weight = 2.38 ± 0.19) or a non-feedback (n = 12, half-squat 3-RM/body weight = 2.03 ± 0.44) group. Both groups performed the same training program (3×week), consisting of 4 sets of 8 repetitions (weeks 1-3) and 8 sets of 4 repetitions (weeks 4-6) using a barbell with a load that maximized the average concentric power output (Pmax) of each athlete. Subjects in the instant feedback group were given real-time data after each repetition. Pre-, mid-, and post-training testing consisted of maximum 20m, 30m and 50m running speed, 3-RM back half-squat load, Pmax and the load that maximized average concentric power output (Pmax load), countermovement (CMJ) and squat jump (SJ) height. Results revealed that the feedback group significantly improved all selected tests versus non-feedback (time×group interaction, p<0.01). Significant improvements post-training for 20m, 30m, 50m, 3-RM load, Pmax load, CMJ and SJ were observed in the feedback group only (p<0.01). Training without instant feedback did not lead to significant performance improvements, this group actually demonstrated significant decreases in SJ and Pmax (W) and Pmax load (p<0.05). The results of this study indicate that the use of instant feedback during jump-squat training in athletes was beneficial for improving multiple performance tasks over 6-weeks of training. Instant feedback is an important element of power training to maximize adaptations when training strength-trained athletes.

The purpose of this study was to determine the changes in the resting level of serum cortisol, testosterone and T/C ratio in response to different training modalities and their variations. A secondary purpose was to identify if the various six weeks training programs are an effective way to improve physical fitness. 86 regularly active young males were assigned to one of six groups: Endurance constant running (ECR), Endurance interval running (EIR), Resistance training (RT), Explosive training (ET), Speed-endurance 50 m running (SER50) and Speed-endurance 150 m running (SER150) training. The resting levels of testosterone, cortisol and T/C ratio, as well as physical fitness, were measured. The ECR, EIR, and RT training program decreased COR level (P < 0.05). An increase of the T/C ratio was observed in the ECR and EIR group (P < 0.05). Except for SER50, each training program improved physical fitness. Our results suggest that endurance and resistance training modalities performed with a moderate to vigorous intensity may be a usable way to manage the resting cortisol level and enhance physical fitness in active young males.