Best Time of Day for Strength and Endurance Training to Improve Health and Performance? A Systematic Review with Meta-analysis

Abstract

Background: Current recommendations for physical exercise include information about the frequency, intensity, type, and duration of exercise. However, to date, there are no recommendations on what time of day one should exercise. The aim was to perform a systematic review with meta-analysis to investigate if the time of day of exercise training in intervention studies influences the degree of improvements in physical performance or health-related outcomes.

Methods: The databases EMBASE, PubMed, Cochrane Library, and SPORTDiscus were searched from inception to January 2023. Eligibility criteria were that the studies conducted structured endurance and/or strength training with a minimum of two exercise sessions per week for at least 2 weeks and compared exercise training between at least two different times of the day using a randomized crossover or parallel group design.

Results: From 14,125 screened articles, 26 articles were included in the systematic review of which seven were also included in the meta-analyses. Both the qualitative synthesis and the quantitative synthesis (i.e., meta-analysis) provide little evidence for or against the hypothesis that training at a specific time of day leads to more improvements in performance-related or health-related outcomes compared to other times. There was some evidence that there is a benefit when training and testing occur at the same time of day, mainly for performance-related outcomes. Overall, the risk of bias in most studies was high.

Conclusions: The current state of research provides evidence neither for nor against a specific time of the day being more beneficial, but provides evidence for larger effects when there is congruency between training and testing times. This review provides recommendations to improve the design and execution of future studies on this topic.

Registration: PROSPERO (CRD42021246468).

Keywords: Cardiovascular; Chronotype; Circadian; Diurnal; Endurance; Meta-analysis; Metabolic; Performance; Strength; Systematic review.

Fig. 1

PRISMA study selection flow diagram

Fig. 2

Description of the exercise interventions in the 22 studies included in the systematic review. Specific information is provided on training load (black/dark gray/light gray circle), type of exercise, time of day of exercise, and total duration of intervention. In addition, details on the sample size (size of the circle) and the existing risk of bias (open/closed circle) are presented for each study

Fig. 3

Meta-analysis of the standardized mean differences (SMD) for the change in performance due to the intervention, calculated as post-intervention value minus pre-intervention value, between morning training and evening training. Positive effect sizes indicate a higher improvement during the intervention period in the evening training condition, while negative effect sizes indicate a higher improvement in the morning training condition

Fig. 4

Meta-analysis of the standardized mean differences (SMD) for the change in performance due to the intervention (i.e., post-intervention value–pre-intervention value) between congruent training and testing in the morning and evening versus incongruent training and testing in the morning and evening for strength (A) and jump performance (C) and between morning exercise (tested both in the morning and evening) and evening exercise (tested both in the morning and evening) for strength (B) and jump performance (D). Positive effect sizes indicate a higher improvement during the intervention period in the evening training condition or with congruent training and testing, while negative effect sizes indicate a higher improvement in the morning training condition or with incongruent training and testing