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Introduction: Advancements in technology have recently made it possible to implement effective training solutions across different environmental conditions. This study evaluated the reliability and validity of measures obtained from the innovative motorized device, Alex7 (Inosportas, Lithuania), and differences in speed and kinematic characteristics between resisted and assisted sprinting in young football players. Methods: Twenty-seven male athletes (mean age: 16.5 ± 0.8 years; height: 179.5 ± 6.9 cm; body weight: 67.7 ± 8.3 kg) each performed 30-m sprints twice under three different conditions: regular, resisted, and assisted sprinting. The Alex7 device provided the assistance and resistance during sprints. Results were compared with those from Witty timing gates. Ground contact time, flight time, stride length, and pace were measured using the OptoJump system. Reliability was assessed using two-way mixed intraclass correlation coefficients (ICCs) for single measures, the standard error of the mean (SEM), and the coefficient of variation (CV). Pearson's correlation coefficient determined the associations between Alex7 and Witty timing systems. Criterion-referenced validity was based on the mean difference and CV. Systematic bias was determined by limits of agreement using Bland-Altman analysis. Results: Running times obtained using the Alex7 equipment exhibited good to excellent test-retest reliability between sessions (ICC, 0.83-0.94) and good to excellent correlation (Pearson's r = 0.88-0.98) between the Alex7 and Witty systems in both assisted and resisted running conditions. However, the Alex7 device consistently produced longer running times than the Witty device (up to 0.16 s difference, p < 0.001). The different running conditions produced substantial variations in kinematic variables, such as stride length, ground contact time, and running speed (p < 0.001 for all), but the effects on flight time and running pace were smaller. Discussion: The Alex7 device shows high reliability for creating resisted and assisted running conditions for young football players. However, it tends to overestimate running time, necessitating caution when assessing the time parameters.

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Carbohydrate (CHO) metabolism is crucial for short-duration, high-intensity exercise performance, but the effects of variations in glycogen availability have not been investigated in field trials of trained athletes. This study was designed to test how 1500 m time trial (TT) performance is affected by the manipulation of pre-race glycogen reserves. Competitive middle-distance runners (n = 11 (4 females)) completed a 1500 m individually paced indoor TT after abundant (high, >5 g/kg/d) or restricted (low, <1.5 g/kg/d) dietary CHO intake for 2 days after a glycogen-depleting session. Stride pattern, heart rate (HR), capillary blood lactate, and glucose and plasma malondialdehyde (MDA) response were determined. The TT was slower in low vs. high condition by 4.5 (4.5) s (~2%; p < 0.01), with a tendency toward shorter stride length. Blood lactate and glucose were lower before the TT in low vs. high condition (1.8 (0.5) vs. 2.2 (0.7) mmol/L and 5.4 (0.7) vs. 5.9 (0.8) mmol/L, p = 0.022 and 0.007, respectively), and peak lactate was higher in high vs. low condition (16.8 (3.1) vs. 14.5 (4.2) mmol/L, p = 0.039). Plasma MDA was the same before the TT, and 15 min after the TT, it increased similarly by 15% in low (p = 0.032) and high (p = 0.005) conditions. The restriction of pre-test CHO intake impaired 1500 m TT performance and reduced baseline and peak blood lactate concentrations but not blood glucose or MDA response.

Asunto(s)

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BACKGROUND: Low-intensity resistance exercises with blood flow restriction have been shown is effective to increase muscular strength and hypertrophy. However, the effects of combined training: one-week occlusion training with various exercise intensities by using less occlusion pressure on muscle strength improvement, fatigability and their work capacity are not clear. METHODS: Participants (N.=24) were middle-distance runners with 4-6 years of training experience. A control group without blood flow restriction (N.=12, age 23±1 years) and an experimental group with blood flow restriction (N.=12, age 22±1 years). In this study, the calf muscles were impacted by the training with occlusion 120 mmHg. We used intensive one-week daily training, whereby exercise intensity was gradually increased daily from 20% to 80% of maximal voluntary contraction (MVC) and then decreased to 60% by the end of the week. RESULTS: MVC of foot flexion muscles after the one-week occlusion training in the experimental group and control group increased (P<0.05) by 5.6±1.3% and 5.3±1.2%, respectively. Meanwhile in experimental group work capacity improved only 2.4±3.5% (P>0.05) and in control group it significantly decreased 11.8±2.5% (P<0.05). StO2 decreased during exercise test from the baseline 100% to 45.2±4.3% before occlusion training and to 34.6±6.2% after the week of occlusion training (P<0.05). CONCLUSIONS: Intensive one-week training with occlusion with varying intensity improves resistance to fatigue and recovery after training. This kind of training improves oxygen consumption while exercising.

Asunto(s)

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Hamstring muscle injuries occur during high-speed activities, which suggests that muscular strength at high velocities may be more important than maximal strength. This study examined hamstring adaptations to training for maximal strength and for strength at high velocities. Physically active men (n = 25; age, 23.0 ± 3.2 years) were randomly divided into: (1) a resistance training (RT, n = 8) group, which performed high-load, low-velocity concentric-eccentric hamstring contractions; (2) a resistance training concentric (RTC; n = 9) group, which performed high-load, low-velocity concentric-only hamstring contractions; and (3) a high-velocity elastic band training (HVT, n = 8) group, which performed low-load, high-velocity concentric-eccentric hamstring contractions. Pre- and posttraining tests included hamstring strength on a hamstring-curl apparatus, concentric knee extension-flexion at 60°/s, 240°/s, and 450°/s, eccentric knee flexion at 60°/s and 240°/s, hamstring and quadriceps coactivation, knee flexion and extension frequency in the prone position, and 30-m sprint running speed from a stationary start and with a running start. Knee flexor torque increased significantly by 21.1% ± 8.1% in the RTC group and 16.2% ± 4.2% in the RT group (p < 0.05 for both groups). Hamstring coactivation decreased significantly in both groups. In the HVT group, knee flexion and extension frequency increased by 17.8% ± 8.2%, concentric peak torque of the knee flexors at 450°/s increased by 31.0% ± 12.0%, hamstring coactivation decreased, and running performance over 30 m improved (p < 0.05 for all parameters). These findings suggest that resistance training at high velocities is superior to traditional heavy resistance training for increasing knee flexor strength at high velocities, movement frequency, and sprint running performance. These findings also indicate that traditional training approaches are effective for increasing knee flexor strength and reducing knee extensor coactivation, but this outcome is limited to low and moderate speeds.

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Electrical myostimulation (EMS) method is applied to improve skeletal muscle function. The aim of this study was to evaluate the efficacy of EMS applied to the sole and calf muscles on their strength and on maximal sprint performance. Each of 10 training sessions involved 10 seconds of stimulation and 50 seconds of rest for a total of 10 minutes. After the 10 training sessions, the maximal voluntary contraction (MVC) of right calf muscles increased by 6.0% from 830.0 ± 47.0 N to 878.0 ± 45.3 N (p ≤ 0.05). When EMS was applied to trained athletes, their 10-m sprint performance improved by 2.1% (p ≤ 0.05). In the second part of the study, a 3-week training program with EMS was applied to athletes, which significantly improved their 10-m sprint performance from a standing start by 5.3% and from a running start by 4.7% (p ≤ 0.05). Thus, 10 EMS cycles up to the maximal tolerated intensity applied every other day improved the MVC of foot flexion muscles and 10-m sprint performance from both standing and running starts. Three weeks of EMS training did not affect the intensity of calf muscle blood flow and oxygen saturation at rest. The training program supplemented with 10 EMS sessions produced significantly greater effects on the 10-m sprint performance from both a standing and a running start.

Asunto(s)

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[Purpose] Occlusion training with low-intensity resistance exercises and blood flow restriction increases muscle cross-sectional area and strength. This form of training is used in rehabilitation; therefore, the aim of this study was to examine the effect of one occlusion training session on the cardiovascular response to bouts of exercise. [Subjects and Methods] Two groups took part: a control group without blood flow restriction and an experimental group with blood flow restriction. A single training session was used with the exercise intensity set at 40% of the one repetition maximum. Maximum voluntary contraction, arterial blood pressure, and electrocardiogram measurements were performed. [Results] Heart rate was slightly higher in the control group. The performed training had no effect on diastolic blood pressure in either group, however, a tendency for a small systolic blood pressure increase was observed during the session in the experimental group. JT interval changes did not reveal significant differences between groups. There were no significant changes in ST-segment depression during the exercise or at rest. A lower tendency for JT/RR increases was observed during the repeated exercise tasks with partial blood flow restriction. [Conclusion] Low intensity exercises carried out with a partial blood flow restriction do not result in significant overload of cardiac function.

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OBJECTIVE: The aim of this study was to find out the characteristics of cardiovascular changes when performing Bosco repeated jumps anaerobic test depending on the duration of jumping in a nonathletes cohort. MATERIALS AND METHODS: Changes in arterial blood pressure indices and changes in 12-lead ECG indices were analyzed. The characteristics of recovery after workloads were assessed by evaluating the time of half period of recovery of registered indices and by the Lyapunov exponent. RESULTS: The results have shown that the ratio of JT and RR intervals of ECG (JT/RR) can be useful for outlining to what extent a cardiovascular function was mobilized. The mobilization of cardiovascular function when performing a 30-s jump test changed up to 0.454±0.012 and when performing a Bosco test, up to the maximal values, i.e. 0.634±0.004. When performing jumps of maximal intensity, a maximal change of JT/RR occurrence was between 50 and 60s. The increasingly serious myocardial ischemic episodes were observed at the onset of the jumping task. The duration of 60-s of all-out jump test has made an influence on the stability of the recovery processes of cardiovascular indices, i.e. the nonexponential type of recovery was observed. CONCLUSIONS: When performing Bosco 60-s repeated jumps in an anaerobic test, a maximal mobilization of the cardiovascular system occurs between 50 and 60s. The 30-s all-out test duration in jumping is enough to outline at what extent cardiovascular function was mobilized as well as to assess other functional characteristics during high intensity intensive exercising.