Twenty-Four-Hour Low Energy Availability Induced by Diet or Exercise Exhibits Divergent Influences on Sleep and Recovery Indices among Female and Male Cyclists.

Abstract

To examine the effects of 24-h manipulations in energy availability (EA), through altering energy intake (EI) or exercise energy expenditure (EEE), on sleep characteristics and nocturnal heart rate variability (HRV). Twenty endurance athletes (10 females, 10 males) undertook five 24-h periods of EA manipulation, separated by 8 d, in a randomized Latin square design. Following 24 h of standardized high EA (45 kcal·kg -1 FFM·d -1 ), athletes then followed a diet providing low EA (15 kcal·kg -1 FFM·d -1 ) either with/without exercise (LEA EX/REST ), high EA (45 kcal·kg -1 FFM·d -1 ) with/without exercise (HEA EX/REST ), and excess EA (75 kcal·kg -1 FFM·d -1 ) without exercise (GEA). Sleep and overnight HRV were assessed using Somfit and Oura ring devices, respectively, pre- and post-EA manipulation. Total sleep duration was extended by 53-61 min following LEA EX versus non-exercise conditions: GEA ( P = 0.002), HEA REST ( P = 0.003), and LEA REST ( P = 0.020). Time in bed was also increased during LEA EX compared with GEA ( P = 0.006) and HEA REST ( P = 0.023), but without alterations to sleep efficiency between conditions ( P = 0.613). Sleep onset latency increased by 8 min following LEA REST compared with GEA ( P = 0.012), whereas there were no other alterations to objective/subjective sleep characteristics between conditions (all P > 0.05). There was no difference in overnight HRV following the 24-h EA manipulation ( P > 0.05). However, mean overnight HR was lower following LEA REST and HEA REST (-4 ± 3 and -2 ± 3 bpm), compared with LEA EX (+1 ± 3 bpm), HEA EX (0 ± 3 bpm), and GEA (0 ± 3 bpm, all P < 0.01). There was no difference between sexes in the response to EA manipulation across all variables. Twenty-four hours of exercise-induced LEA extended total sleep time, whereas diet-induced LEA reduced mean overnight HR. The responses to EA manipulations did not differ between sexes.