Dose and timing effects of caffeine on subsequent sleep: A randomised clinical crossover trial.

STUDY OBJECTIVES: To investigate the effect of a typical dose of caffeine and a high dose of caffeine consumed in the morning, afternoon, and evening on subsequent sleep. METHODS: Using a placebo-controlled, double-blind, randomised crossover design, 23 males (25.3±5.0 years) with a moderate habitual caffeine intake (<300mg∙day-1) completed seven conditions: placebo, and 100 and 400mg of caffeine consumed 12, eight, and four hours prior to bedtime, with a 48-hour washout. In-home partial polysomnography and sleep diaries were used to assess sleep. Linear mixed models estimated the effect of each condition. RESULTS: No significant effect on objective or subjective sleep occurred with the 100mg dose of caffeine compared to the placebo (p>0.05) but significant effects occurred with the 400mg dose (p<0.05). Significant delays in sleep initiation and alterations to sleep architecture were observed when 400mg was consumed within 12 hours of bedtime (p<0.05), and significantly greater sleep fragmentation occurred when 400mg was consumed within eight hours of bedtime (p<0.05). Additionally, perceived sleep quality was significantly reduced when 400mg was consumed four hours prior to bedtime (-34.02%, p=.006) but not at eight or 12 hours. CONCLUSIONS: A 100mg dose of caffeine can be consumed up to four hours prior to bedtime, but 400mg may negatively impact sleep when consumed as one dose within 12 hours of bedtime, with the adverse influence on sleep increasing the closer consumption occurs to bedtime. The discrepancy between objective and subjective sleep quality suggests individuals may have difficulty accurately perceiving the influence of caffeine on sleep quality.

Comparison of Sprint Timing Methods on Performance, and Displacement and Velocity at Timing Initiation.

ABSTRACT: Weakley, J, McCosker, C, Chalkley, D, Johnston, R, Munteanu, G, and Morrison, M. Comparison of sprint timing methods on performance, and displacement and velocity at timing initiation. J Strength Cond Res 37(1): 234-238, 2023-Sprint testing is commonly used to assess speed and acceleration in athletes. However, vastly different outcomes have been reported throughout the literature. These differences are likely due to the sprint timing method rather than differences in athlete ability. Consequently, this study compared different sprint starting methods on sprint time and quantified the velocity and displacement of the athlete at the moment timing is initiated. Starting in a staggered 2-point stance, 12 team sport athletes were required to accelerate 10 meters for 10 repetitions. During each repetition, 5 independent timing methods were triggered. The methods were (a) triggering a Move sensor; (b) starting 50 cm behind the line; (c) triggering a front-foot switch; (d) triggering a rear-foot switch; and (e) starting with the front foot on the line. Timing for each method was initiated at different points during the acceleration phase, and the displacement and velocity of the centroid of the pelvis at the point of timing initiation was assessed under high-speed motion capture. The Move sensor had the smallest displacement and lowest velocity at the point of timing initiation, whereas the front-foot trigger demonstrated the largest displacement and highest velocities. Trivial to very large effect size differences were observed between all methods in displacement and velocity at the point of timing initiation. Furthermore, small to very large differences in time to 5 m were found. These findings emphasize that sprint outcomes should not be compared, unless starting methods are identical. In addition, to detect real change in performance, consistent standardized protocols should be implemented.

The Criterion Validity and Between-Day Reliability of the Perch for Measuring Barbell Velocity During Commonly Used Resistance Training Exercises.

ABSTRACT: Weakley, J, Munteanu, G, Cowley, N, Johnston, R, Morrison, M, Gardiner, C, Pérez-Castilla, A, and García-Ramos, A. The criterion validity and between-day reliability of the Perch for measuring barbell velocity during commonly used resistance training exercises. J Strength Cond Res 37(4): 787-792, 2023-This study aimed to assess the criterion validity and between-day reliability (accounting for technological and biological variability) of mean and peak concentric velocity from the Perch measurement system. On 2 testing occasions, 16 subjects completed repetitions at 20, 40, 60, 80, 90, and 100% of 1-repetition maximum in the free-weight barbell back squat and bench press. To assess criterion validity, values from the Perch and a 3-dimensional motion capture system (criterion) were compared. Technological variability was assessed by determining whether the differences between the Perch and criterion for each load were comparable for both testing sessions, whereas between-day reliability with both technological and biological variability was calculated from Perch values across days. Generalized estimating equations were used to calculate R2 and root mean square error, whereas Bland-Altman plots assessed magnitude of difference between measures. To support monitoring of athletes over time, standard error of measurement and minimum detectable changes (MDC) were calculated. There was excellent agreement between the Perch and criterion device, with mean velocity in both exercises demonstrating a mean bias ranging from -0.01 to 0.01 m·s -1 . For peak velocity, Perch underestimated velocity compared with the criterion ranging from -0.08 to -0.12 m·s -1 for the back squat and -0.01 to -0.02 m·s -1 for the bench press. Technological variability between-days were all less than the MDC. These findings demonstrate that the Perch provides valid and reliable mean and peak concentric velocity outputs across a range of velocities. Therefore, practitioners can confidently implement this device for the monitoring and prescription of resistance training.