Purpose: High-intensity interval training (HIIT) has emerged as a time-efficient alternative to traditional endurance training. This study investigated the molecular, systemic, and physiological adaptations induced by an 8-week HIIT program in national-level flatwater kayak athletes. Methods: Six trained male kayakers completed an 8-week HIIT intervention. Skeletal muscle biopsies and venous blood samples were collected before and after training to assess markers related to endocrine function, growth and remodeling, angiogenesis, and inflammation. Physiological and performance measures were evaluated using a maximal oxygen uptake (VO₂max) test and kayak ergometer trials. Results: HIIT elicited significant improvements across molecular, systemic, and performance parameters. Post-training analyses showed increased expression of IGF-1R, MMP-4, MMP-9, and TNF-α (p < 0.05), along with elevated serum testosterone concentrations (p < 0.05). Notable performance gains were observed in paddling speed at the second ventilatory threshold (PSVT2; p < 0.05) and in 1000 m (p < 0.01) and 200 m (p < 0.001) time-trial performances. Conclusions: An 8-week HIIT program effectively enhanced molecular signaling, systemic adaptation, and sport-specific performance in elite flatwater kayak athletes. The concurrent upregulation of anabolic, remodeling, and inflammatory pathways suggests that HIIT facilitates coordinated muscular and systemic adaptations beneficial for kayak performance.

Background: This study examined the impact of aerobic capacity on force–velocity (F–v) variables and repeated-sprint (RS) performance in male national-level sprinters (SPRs, n = 8; 177.0 ± 4.3 cm; 74.0 ± 5.0 kg; maximal oxygen uptake [VO₂max]: 55.4 ± 3.0 mL/kg/min) and middle-distance runners (MDRs; n = 8; 179.0 ± 5.1 cm; 67.2 ± 5.0 kg; VO₂max: 64.3 ± 3.3 mL/kg/min). Method: Participants underwent assessments of aerobic capacity, mechanical F-v profiling in sprinting 2 × 60 m with full recovery, and a 10 × 60 m repeated-sprint test with 30 s recovery. Results: MDRs exhibited significantly higher VO₂max (p < 0.001) and speed at VO₂max (vVO₂max, p < 0.001), while SPRs demonstrated greater anaerobic speed reserve (ASR, p < 0.001), maximal theoretical horizontal force (F₀, p = 0.012), and power output (P_max, p < 0.01). During the RS test, SPRs displayed a 16.6% performance decrement (p = 0.002) and failed to complete all sprints with voluntary withdrawal after 5–8 sprints due to exhaustion, whereas MDRs maintained consistent performance. SPRs exhibited a larger decrease in v₀ compared to MDRs (p < 0.01), whereas no differences were observed on F₀ (p = 0.519) and P_max (p = 0.758). Blood lactate accumulation was higher in SPRs (p < 0.001). Multiple linear regression analysis on the pooled sample identified vVO₂max (p = 0.003) and not ASR (p = 0.482) as a key predictor of fatigue resistance. Conclusions: These findings underscore the critical role of aerobic capacity in sustaining RS performance. Aerobic capacity, specifically vVO₂max, emerged as the primary determinant of fatigue resistance during repeated sprints, underscoring its critical role in sustaining RS performance over mechanical variables such as v₀ but not F₀ and P_max.

Background/Objectives: This study aimed to examine the post-activation performance enhancement effects of bilateral horizontal drop jumps (BHDJs) on 30 m sprint and countermovement jump (CMJ) performance, as well as in sprint mechanical and kinematics characteristics. Methods: Fourteen young sprinters (nine boys and five girls) completed both an experimental condition (EC) and a control condition (CC). The EC consisted of five BHDJs performed at each participant’s individually determined optimal drop height, whereas in the CC, no exercise has been performed. Results: The findings revealed no significant (p > 0.05) interactions for CMJ and time to 30 m. Significant increases in 5 m split times were observed across all segments in the CC, as well as in the initial 5 m segment in the EC. Regarding sprint mechanics, a significant interaction was found in the effectiveness of horizontal force application (−2.42% in CC vs. −0.33% in EC). Step frequency demonstrated significant interaction in the 5–10 m segment (−1.79% in CC vs. 1.20% in EC) and decreased significantly in the 15–20 m segment in the CC (−2.03% in CC vs. −1.85% in EC). Conclusions: In conclusion, performance parameters reduced under the CC, whereas the BHDJ intervention stabilized these parameters or exhibited smaller performance variations than in the CC.

AIM: There is some evidence to suggest that exercise in the evening, compared with exercise in the morning, has a more beneficial impact on glycemia in patients with type 2 diabetes (T2D). The aim of this study was to examine a possible acute effect of aerobic exercise performed at different times of day on blood glucose levels during and after exercise in patients with T2D. MATERIAL & METHOD: Eight male T2D patients (61.8 ± 6.9 yrs, 27.7 ± 3.1 kg/m², HbA1c: 6.5 ± 1.1%; mean ± SD), who did not receive insulin, performed 60-min cycling at about 75% maximal heart rate (HRmax) either at 10:30 (Morning-M), or at 17:30 (Evening-E), or 30-min cycling at 10:30 and 30-min cycling at 17:30 (ME). A control condition (C) was also included where volunteers did not exercise but had their blood glucose measured at day-time intervals similar to the time intervals of the three exercise trials. Two days before each condition no physical activity was allowed, while the day before and on the day of each trial participants controlled their diet. RESULTS: Compared to resting levels, blood glucose at the end of exercise decreased at similar levels in M (20 ± 12%), E (28 ± 14%), in the morning of ME (21 ± 10%) and in the evening of ME (26 ± 19%) (p > 0.05). Also, heart rate, blood lactate and rate of perceived exertion responses during exercise were similar between the 3 exercise conditions. Mean area under the blood glucose-time curve over the two-hour post-exercise period in exercise trials, and at similar time intervals in C, was different only between the morning in C (15,173 ± 1830 mg/dL•120 min) and the evening in ME (11,681 ± 1526 mg/dL•120 min, p = 0.045). In addition, overnight fasting serum glucose the morning after each trial was similar between conditions (p > 0.05). CONCLUSIONS: No acute effect of cycling at about 75% HRmax was observed on glycemia in patients with T2D when exercise was performed at different times of day.