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The time-of-day effect of exercise on human function remains largely equivocal. Hence, this study aimed to further analyze the existing evidence concerning diurnal variations in cardiorespiratory responses and endurance performance using a meta-analytic approach. Literature search was conducted through databases, including PubMed, CINAHL, and Google Scholar. Article selection was made based on inclusion criteria concerning subjects' characteristics, exercise protocols, times of testing, and targeted dependent variables. Results on oxygen uptake (VO2), heart rate (HR), respiratory exchange ratio, and endurance performance in the morning (AM) and late afternoon or evening (PM) were extracted from the chosen studies. Metaanalysis was conducted with the random-effects model. Thirty-one original research studies that met the inclusion criteria were selected. Meta-analysis revealed higher resting VO2 (Hedges' g = -0.574; p = 0.040) and resting HR (Hedges' g= -1.058; p = 0.002) in PM than in AM. During exercise, although VO2 remained indifferent between AM and PM, HR was higher in PM at submaximal (Hedges' g = -0.199; p = 0.046) and maximal (Hedges' g = -0.298; p = 0.001) levels. Endurance performance as measured by time-to-exhaustion or the total work accomplished was higher in PM than in AM (Hedges' g = -0.654; p = 0.001). Diurnal variations in VO2 appear less detectable during aerobic exercise. The finding that exercising HR and endurance performance were greater inPMthan in AMemphasizes the need to consider the effect of circadian rhythm when evaluating athletic performance or using HR as a criterion to assess fitness or monitor training. [ABSTRACT FROM AUTHOR]

Kusumoto, H, Ta, C, Brown, SM, and Mulcahey, MK. Factors contributing to diurnal variation in athletic performance and methods to reduce within-day performance variation: A systematic review. J Strength Cond Res 35(12S): S119–S135, 2021—For many individuals, athletic performance (e.g., cycle ergometer output) differs based on the time of day (TOD). This study identified factors contributing to diurnal variation in athletic performance and methods to reduce TOD performance variation. Comprehensive searches of PubMed, Ovid, EMBASE, Web of Science, and Cochrane Libraries were conducted in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Peer-reviewed publications reporting quantitative, significant diurnal variation (p ≤ 0.05) of athletic performance with explanations for the differences were included. Studies providing effective methods to reduce diurnal variation were also included. Literature reviews, studies involving nonhuman or nonadult subjects, studies that intentionally manipulated sleep duration or quality, and studies deemed to be of poor methodological quality using NIH Quality Assessment Tools were excluded. Forty-nine studies met the inclusion criteria. Body temperature differences (n = 13), electromyographic parameters (n = 10), serum biomarker fluctuations (n = 5), athlete chronotypes (n = 4), and differential oxygen kinetics (n = 3) were investigated as significant determinants of diurnal variation in sports performance. Successful techniques for reducing diurnal athletic performance variability included active or passive warm-up (n = 9), caffeine ingestion (n = 2), and training-testing TOD synchrony (n = 3). Body temperature was the most important contributor to diurnal variation in athletic performance. In addition, extended morning warm-up was the most effective way to reduce performance variation. Recognizing contributors to diurnal variation in athletic performance may facilitate the development of more effective training regimens that allow athletes to achieve consistent performances regardless of TOD. [ABSTRACT FROM AUTHOR]

The aim of this study was to analyze the acute effects of resistance training (RT) systems on lower- and upper-limb performance in trained adults. Eighteen male young adults with experience in RT aged from 18 to 26 years underwent the 3 experimental conditions (drop-set [DS], decrescent pyramid [DP], and traditional [TR]). The subjects performed 2 exercises (bench press and leg press 45°). In the DS condition, they underwent 2 sets of 10 repetitions at 12RM, followed by 5 additional repetitions with an intensity of 15RM with 6-minute interval rest between sets. In the DP, it was performed 3 sets of 10 repetitions at 10RM, 12RM, and 15RM, respectively, and the rest interval was 3 minutes between sets. In the TR, the subjects performed 3 sets of 10 repetitions at 12RM with 3 minutes of rest between sets. Countermovement jump, peak power (Wpeak), and force (Fpeak) in the bench press were evaluated in the baseline, before, and 30 minutes after the experimental sessions. Countermovement jump performance decreased significantly only after the DS and DP conditions (26.7 and21.9%, respectively). The groups were significantly different in the post-intervention; the DS condition presented lower values when compared with the DP (p 5 0.01) and TR (p 5 0.001). According to Fpeak and Wpeak, only DS condition significantly decreased the performance (23.8 and 24.1%, respectively). The results indicate the DS and DP conditions impair the neuromuscular performance of the lower limbs, whereas for upper limbs, only DS condition negatively affect upper-limb performance. [ABSTRACT FROM AUTHOR]

Carbohydrate (CHO) mouth rinsing rapidly increases corticomotor output and maximal muscle force production, which could enhance muscular strength and endurance during resistance exercise. However, previous research has found no effect of CHO rinsing on muscular strength or endurance. The current study altered the CHO rinse composition and frequency and the muscular endurance test to further investigate the effects of a CHO mouth rinse on upper-body muscular strength and endurance. Twelve recreationally resistance-trained men (mean ± SD age 22 ± 1 year, height 179.2 ± 1.8 cm, body mass 80.9 ± 6.1 kg) completed a bench press protocol (1 repetition maximum [RM] test followed by repetitions to failure at 40% of 1RM) on 3 occasions. Subjects rinsed 25 ml of an 18% CHO solution or a placebo for 10 seconds before 1RM and repetitions to failure and completed a no-rinse control condition. Felt arousal (FA) was measured before and after each rinse, heart rate (HR) was measured before and after both exercise protocols, and rating of perceived exertion (RPE) was recorded after repetitions to failure. Rinsing did not influence 1RM (p = 0.680, ηp² = 0.03), repetitions to failure (p = 0.677, ηp² = 0.04), or exercise volume (load x reps; p = 0.600, ηp² = 0.05). There were no significant treatment effects on heart rate (p = 0.677, ηp² = 0.04), FA (p = 0.674, ηp² = 0.04) or rating of perceived exertion (p = 0.604, ηp² = 0.05). A CHO mouth rinse does not improve upper-body muscular strength or endurance. [ABSTRACT FROM AUTHOR]

It is well established that many physiological functions are time-of-day (TOD) dependent, and their circadian rhythms are well documented in healthy populations at resting state. In fact, greater rate of oxidative stress, white blood cell, homocysteine, and muscle damage markers were shown in the early evening (≈ 18:00 hours), and more efficient antioxidant activity was observed in the early morning (≈ 06:00 hours). During physical tasks, the majority of the above-mentioned physiological functions increase from pre to post physical exercise with different rates of increases from morning to evening. These different rates of increases are suggested to alter the physiological resting diurnal variation. In this context, given the possible significant interaction "TOD x physical exercise," circadian rhythms of the physiological responses during physical activity are still not well established in trained subjects. Otherwise, it was suggested that the diurnal variation of these biochemical parameters could, in part, explain the typical diurnal fluctuation of physical performance. Therefore, the aim of this review was to summarize the currently available studies investigating the circadian rhythms of physiological functions at rest and after physical exercise and to establish their possible effect on the diurnal variation of sport performance. Although studies in this field are limited, the available information shows that compared with sedentary subjects, trained population maintained similar diurnal variations of hematological parameters, homocysteine, and some biochemical markers at rest and even after physical exercise. However, after strength exercises, the circadian rhythms for the majority of oxidative stress and muscle damage markers were altered because of the higher rate of increased pre-post exercises registered in the morning compared with the afternoon and evening. The available studies reveal that the significant circadian variation observed for sport performances could be more likely explained by the alteration of ionic movement and the diurnal fluctuation of homocysteine, lactate, muscle damage, and antioxidant markers. [ABSTRACT FROM AUTHOR]

The authors discuss a study which has identified that blunted and persistent diurnal variations of muscular anaerobic exercises can result from strength training. They state that an anaerobic performance can be enhanced by effective adjustment to sleep-wake cycle. The authors note that the minimum of circadian rhythms is the basis for morning and evening tests.