Journal of the International Society of Sports Nutrition最新文献

Introduction: Caffeine has been shown to improve endurance performance probably primary due to its pharmacological effects in the central nervous system modifying, among others, the perceptual responses during exercise. However, most studies proving the performance-enhancing effects of caffeine utilized an experimental caffeine restriction phase prior to the measurement sessions. Therefore, the effects of 2.5 and 6 mg*kg^-1 oral caffeine ingestion on endurance performance, perceptual, affective, and cognitive responses during exercise, as well as time perception, were investigated in participants following their normal "ad libitum" daily diet.

Methods: Two double-blinded, randomized placebo-controlled cross-over studies were performed to test the effect of 2.5 (N = 35, age: 23.3 ± 3.5 years, habitual caffeine consumption of 106 ± 89 mg*day^-1) and 6.0 mg*kg^-1 (N = 21, age: 21.2 ± 2.3 years, habitual caffeine consumption of 87 ± 64 mg*day^-1) oral caffeine ingestion on time to exhaustion (TTE), perceived fatigue, perceptual-discriminatory (effort perception, physical strain), affective-motivational (affective valence, arousal, dominance, motivation, boredom), and cognitive-evaluative responses (decisional conflict, attentional focus) as well as time perception (time production and estimation) and heart rate during cycling at 65% peak power. Participants were low-to-moderate caffeine consumers (one participant in each study reported no habitual caffeine intake) and asked to follow their regular "ad libitum" diet without any restrictions regarding caffeinated beverages and/or food during the studies.

Results: Neither a dose of 2.5 nor of 6.0 mg*kg^-1 was found to be superior to placebo with respect to TTE, perceived fatigue, the perceptual-discriminatory, affective-motivational, and cognitive-evaluative responses to exercise, as well as time perception.

Conclusion: Both dosages of caffeine had no effect on TTE, perceived fatigue, perceptual-discriminatory, affective-motivational, and cognitive-evaluative responses to exercise, as well as on time perception and heart rate in low-to-moderate caffeine consumers without a prior experimental caffeine restriction phase. The findings suggest that caffeine´s positive effects on endurance performance and perceptual responses to exercise found in previous studies might be partly explained by the reversal of adverse effects induced by a prior caffeine restriction phase.

Purpose: This study aimed to investigate and compare the effects of chronic supplementation with L-Citrulline (LC) vs. L-Citrulline DL-malate (CM) on resistance training (RT) performance.

Methods: Thirty-three resistance-trained men were randomly assigned to ingest LC (8 g), CM (12 g), or Placebo (PL) daily, along with participation in a 6-week RT protocol. Muscular strength (1-repetition maximum [1RM] for hack squat [HS] and bench press [BP]), muscular endurance (repetitions to failure [RTF] for HS, leg extension [LE], BP, and incline press [IP]), rating of perceived exertion (RPE), and blood biomarkers (lactate, urea, and nitric oxide metabolites [NO_X]) were assessed before and after the intervention. This study was registered on irct.ir (IRCTID: IRCT20221128056642N1).

Results: Comparing mean ∆ scores revealed a significant difference between LC and PL (p < 0.001) and between CM and PL (p = 0.026) for total upper body (the sum of BP and IP) RTF, but only a trend for difference between LC and PL (p = 0.070) for total lower body (the sum of HS and LE) RTF. A significant time effect for NO_X was detected only for LC (p = 0.014) and CM (p = 0.003). In addition, a significant difference between CM and PL (p = 0.009) and a marginally significant difference between LC and PL (p = 0.057) was detected regarding post-exercise NO_X values at post-intervention. There were no other between-group differences for any outcome measure.

Conclusion: Chronic citrulline supplementation seems to enhance upper body muscular endurance and post-exercise NO_X response to RT, but there is no apparent difference between LC and CM in these aspects.

Background: Studies have demonstrated that both transcranial direct current stimulation (tDCS) and caffeine improve cognitive abilities through similar mechanisms. This study investigated the acute effects of tDCS combined with caffeine on executive functions.

Methods: Eighty females were randomly assigned to four groups (tDCS + caffeine, tDCS + placebo, sham tDCS + caffeine, and sham tDCS + placebo). Each participant completed two experimental sessions. In the first session, participants performed the Stroop, 3-back, and More-Odd Shifting tasks (T0). For the second session, participants ingested a 200 mg caffeine capsule/placebo, waited 45 minutes, and then received 2 mA real or sham tDCS for 20 minutes. Next, they performed the same cognitive tasks as in the first session (T1), and rested for 30 minutes before completing the cognitive test again (T2).

Results: Accuracy in the 3-back task was significantly improved for the tDCS + caffeine group at T1 and T2, for the tDCS + placebo group at T1, and for the sham tDCS + caffeine group at T2 compared to the sham tDCS + placebo group. Accuracy on the Stroop task was significantly enhanced in the tDCS + caffeine group at T1 compared to the sham tDCS + caffeine and sham tDCS + placebo groups, and in the tDCS + placebo group at T1 compared to the sham tDCS + caffeine group. No significant differences were observed among groups for the More-Odd Shifting task.

Conclusions: These findings suggest that both tDCS and caffeine interventions can improve cognitive task performance, and their combination results in more persistent improvements in executive functions compared to tDCS or caffeine alone.

Background: Sodium bicarbonate (SB) supplementation may enhance short-term, high-intensity exercise performance through improved extracellular buffering capacity, but its effect on continuous running performance has not been systematically evaluated. We conducted a systematic review with meta-analysis of randomized, double-blind, placebo-controlled trials examining the effects of oral single-dose SB supplementation on continuous running performance.

Methods: We searched Medline, Embase, and the Cochrane Central Register of Controlled Trials for eligible trials published through 31 December 2024. The primary outcome was performance on a continuous running test. Secondary outcomes included gastrointestinal (GI) symptoms and GI-associated study withdrawal rates. Running performance was analyzed using random-effects meta-analysis with adjustment for GI-related study withdrawals using intent-to-treat methods and publication bias using the trim-and-fill method. Treatment effects were reported using the standardized mean difference (SMD) statistic where 0.00-0.19 represents negligible benefit, 0.20-0.49 small benefit, 0.50-0.79 medium benefit, and ≥ 0.80 large benefit. We used univariable meta-regression to examine factors associated with treatment effect magnitude. The certainty of evidence was assessed using the GRADE (Grading of Recommendations Assessment, Development and Evaluation) approach.

Results: Among 11 studies with 126 participants, all used a cross-over design. Most (84%) subjects were male, SB dose was typically 0.3 g/kg, and performance test durations ranged from 1 to 30 minutes (median: 4 minutes). GI symptoms occurred more frequently with SB than placebo (29.5% vs. 2.6%; odds ratio = 5.9; p = 0.003; low certainty), as did GI-related study withdrawal (8.7% vs. 1.6%; odds ratio = 2.9; p = 0.049; moderate certainty). After adjusting for GI-related study withdrawal and publication bias, the treatment effect of SB was negligible and not statistically significant (SMD = 0.18; 95% CI: -0.01, 0.36; p = 0.06; I² = 0%; moderate certainty). In meta-regression, male sex (p = 0.03) and higher body mass (p = 0.04) were associated with greater SB performance benefits. In the 8 studies that enrolled males only, the treatment effect of SB was small and statistically significant (SMD = 0.40; 95% CI: 0.18, 0.63; p < 0.001).

Conclusions: SB supplementation has a negligible benefit on continuous running performance in a mixed-sex population, the ergogenic effect may be more pronounced in males, GI symptoms are common, and some users may not tolerate supplementation. Athletes should carefully weigh the potential performance benefit of SB against the risk of GI symptoms and establish individual tolerance during training before considering use during competition.

Background: Snake fruit is rich in vitamin C, carotene, phenolic compounds, flavonoids, and monoterpenoids - bioactive constituents known for their potent antioxidant properties. Based on these components, the present study investigated the potential effects of snake fruit jelly ingestion on glycemic control, endurance performance, alongside its impact on antioxidant status, inflammatory responses, and metabolic biomarkers in healthy individuals.

Methods: A randomized crossover design was used in two separate experiments involving 48 healthy sedentary men and women aged 19-35 years. All participants ingested 140 g of both control jelly and snake fruit jelly on separate occasions. Experiment 1 (n = 25): Blood glucose (BG) concentrations were measured at baseline and every 30 minutes for 2 hours post-ingestion. Experiment 2 (n = 23): Following each jelly ingestion, participants performed leg cycling at 60% of peak oxygen consumption until exhaustion. Blood samples were collected before and after exercise to measure BG, insulin, cortisol, and biomarkers of antioxidant status and inflammation.

Results: In Experiment 1, BG concentrations at 30 and 60 minutes post-ingestion, as well as the incremental area under the BG curve at 30, 60, 90, and 120 minutes, were significantly lower following snake fruit jelly ingestion compared with control (all p < 0.05). In Experiment 2, post-exercise superoxide dismutase (SOD) activity was significantly increased, while tumor necrosis factor-alpha (TNF-α) and cortisol concentrations were significantly decreased after snake fruit jelly ingestion (all p < 0.05). Between-group analysis revealed that endurance time and SOD activity were significantly higher, whereas BG, insulin, and TNF-α concentrations were significantly lower following snake fruit jelly ingestion compared with control jelly ingestion (all p < 0.05). Cortisol and interferon-gamma concentrations showed no significant differences between conditions.

Conclusion: Acute ingestion of snake fruit jelly enhances glycemic control, endurance performance, and antioxidant activity, while reducing blood glucose, insulin, and pro-inflammatory markers in response to endurance exercise.

Clinical trial registration: Retrospectively registered at ClinicalTrials.gov (Identifier: NCT06227260).

Background: There is growing recognition of Low Energy Availability (LEA) symptoms in physique sports, however there are no clear recovery guidelines. This study explores how athletes perceive and manage recovery from prolonged and intentional LEA. Findings will inform future recovery strategies aimed at restoring energy availability.

Methods: Semi-structured interviews were conducted with 19 natural physique athletes (11 males, 8 females) from Australia, New Zealand, North America, and Europe, and data were analyzed thematically.

Results: Five themes were identified relating to weight management experiences pre- and post-competition: (1) pride, suffering, and rationalizing LEA, (2) navigating energy restoration, (3) body image disruption, (4) evolving autonomy, and (5) opportunities for supporting recovery. Perceived recovery was influenced by the severity of energy restriction, coaching support, and athlete readiness. Athletes voiced that psychological flexibility and physiological literacy were interconnected with successful outcomes.

Conclusions: Athletes experience benefit from early recovery planning, applying flexible approaches to nutrition and training post-competition, and a shift from aesthetic to functional goals. Identified themes support treating recovery as a deliberate and individualized phase within the competitive cycle, with further investigation needed on optimizing post-LEA refeeding and coaching practices.