Sprint Interval Training and Endurance Exercise Performance: Influence of Constant vs Variable Time of Day of Training and Time of Assessment

• Published in: The FASEB journal 2020-04, Vol.34 (S1), p.1-1
• Main Authors: Ewell, Taylor Russell, Harms, Kole Jerel, Abbotts, Kieran Shay Struebin, Bell, Christopher
• Format: Article
• Language: English
• ISSN: 0892-6638; 1530-6860
• DOI: 10.1096/fasebj.2020.34.s1.04978

Abstract only In light of the many demands competing for our attention in today’s modern lifestyle, scheduling healthy behaviors, such as daily exercise, at or around the same time of day can be difficult. Accordingly, the purpose of this study was to compare the endurance benefits of short‐term sprint interval training (SIT) when SIT was completed at a constant or variable time of day. The influence of the time of day of assessment relative to the time of day of training was also examined. SIT consisted of six sessions of 4‐to‐7 x 30‐second sprints on a stationary cycle ergometer completed over two weeks. Endurance exercise performance was assessed via a laboratory‐based cycle ergometer time trial equivalent to 10‐km. Two habituation time trials were completed prior to pre‐SIT assessment. Twenty healthy adults (age: 23 ± 7 years, body mass index: 24.7 ± 3.0 kg/m 2 , maximal oxygen uptake: 44 ± 9 ml/kg/min (mean ± SD)) were randomly assigned to one of two training conditions: (1) Constant (6 males, 3 females), in which all training and pre/post time‐trials occurred at a fixed time of day that was not necessarily the same time for each participant; or, (2) Variable (7 males, 4 females), in which all training was scheduled such that each session never occurred within 6‐hours of the time of day of the previous session; post‐SIT time trials for the Variable group were completed at the same time of day as pre‐SIT time trials. A second post‐SIT time trial (Post2) was scheduled for all participants to occur at a time of day a minimum of 6‐hours earlier/later than the time of day of the first post‐SIT time trial. SIT improved time trial performance (main effect P =0.019) but only when the time trial did not occur at the same time of day as training (i.e. Post2); the magnitude of improvement was not influenced by whether the training was completed at a constant or variable time of day (Constant: Pre 1153 ± 173, Post 1136 ± 179, & Post2 1123 ± 154 s vs . Variable: Pre 1186 ± 159, Post 1166 ± 158, & Post2 1149 ± 130 s; group x training interaction P =0.646). SIT did not influence body mass or composition, as determined by dual energy X‐ray absorptiometry (all P >0.34). At the start of each SIT session, oral temperature was measured. The co‐efficient of variation appeared lower for the Constant compared with the Variable group (0.6 ± 0.3 vs . 1.1 ± 0.7%; P =0.099). Our preliminary data suggest that SIT improves endurance exercise performance when assessed at a variabl