Training effect during the polar night in different chronotypes

Introduction: In a previous study we have found that adults with different chronotypes have responded differently to exercise performed in day-light or darkness (Vitale, Calogiuri, & Weydahl, 2013). Above 70 dgr North, the sun is. not above the horizon for about 8 weeks, giving the people living there very little daylight. The aim of this paper is to study the effect of training during the polar nights in relation to the individual’s chronotype. To the best of our knowledge, no past studies investigated this topic. Method: We used Horne and Östberg questionnaire to determine chronotype in 265 inhabitants wanting to participate. 10 M-, 10N- and 10 E-types were chosen to participate. The last week before the polar night, we found the participants’ anaerobic lactic acid profile (AT) and their maximal oxygen consumption (VO2 max) (test 1). During the polar night period the participants trained in a group one hour out-of-doors and one hour indoors each week in addition to every-day homework, like going outside at least 10 minutes and some flexibility, balance and strength exercise. The week after the polar night, the subjects were retested (test 2), Subjects that did not participate in training or test 2 were excluded in the further analyses. We run multiple regression analyses to check for a possible relationship between chronotype and the % of changes from test 1 to test 2. Results: Fifteen subjects completed the study: 8 females and 7 males with mean age 37 years, BMI: 28. They were 3 E-types, 5 N-types and 7 M-types. Mean values at test 1: VO2max: 36.9 ml/min x kg and HR at AT: 82% of HRmax. No significant relations were observed from multiple regression analyses looking at the % of changes in VO2 max (R2: 0.07, p=0.369) and AT (R2: 0.02 p=0.61) and the MEQ scores of each subjects. The data for VO2max and AT were normally distributed therefore we performed a paired t-test from test 1 to test 2 conditions for the whole group. We observed that the subjects increased significantly their VO2 max (from 36.9 to 39.6 with a p=0.02). Discussion: The increased VO2max is expected since the subjects trained for several weeks nevertheless, this increase was significant only for E-types and N-types but no for M-types. We can hypothesized that M-types did not increase their VO2 max because they were disadvantaged during the training period with darkness. We did not observe a real overall chronotype effect on test results performed after the period of polar nights. The group size is a limiting factor, it is advisable to continue the study to include more subjects. References: Vitale, J. A., Calogiuri, G., & Weydahl, A. (2013). Influence of chronotype on responses to a standardized, self-paced walking task in the morning vs afternoon: A pilot study 1. Perceptual & Motor Skills, 116(3), 1020-1028.