Chronotypical and Habitual Exercise Timing Effects on Physical Activity and Sleep Quality

An individual\u27s circadian rhythm and chronotype, or circadian preference, influence physical activity (PA) and sleep patterns during the 24-hour period, with people who prefer later exercise exhibiting poorer sleep patterns and reduced physical activity (PA) levels. Previous work comparing exercise timing’s relationship with chronotype examined single bouts of exercise, indicating the need to examine habitual exercise trends on a longer-term basis. PURPOSE: To analyze the interaction between chronotype and long-term exercise timing preference on physical activity and sleep quality. METHODS: Data were analyzed retrospectively from an open-source data set collected by Cunningham et al. from 05/2020 – 11/2021. Chronotype was determined using the reduced Morningness-Eveningness Questionnaire (rMEQ) along with daily questionnaires throughout 2020 and 2021 where participants self-reported exercise timing and step count. PA was reported as a percent of exercise days to total days responded. Habitual exercise timing (time of day, TOD) was categorized as \u3e33% of their reported exercise completed in the morning, afternoon, or evening. Sleep quality was assessed using the Pittsburgh Sleep Quality Index (PSQI) and the Insomnia Severity Index (ISI). Two-way ANOVA was used to determine the interaction between TOD of exercise and chronotype. RESULTS: From 05/2020 – 11/2021, participants averaged 67 daily questionnaire responses. PA and step count was higher among earlier chronotypes (main effect [ME] Chronotype; pCONCLUSION: The 67 average responses allowed us to create robust exercise timing groups and analyze patterns larger than a single bout of exercise. Supporting previous literature, later chronotypes are less physically active and exhibit worse sleep quality, regardless of the individual\u27s habitual exercise timing. Further investigation is necessary to determine cardiovascular or wellness consequences of later chronotypes performing reduced physical activity

Effects of Social Jetlag on Exercise-Induced Adaptations in Skeletal Muscle Mitochondrial Content in Mice

Social jetlag (SJL) occurs when the sleep/wake schedule differs on work days (weekdays) and free days (weekends). Previous studies have shown that individuals with SJL have lower physical fitness and are prone to obesity. While exercise reverses this phenotype (i.e. - via increasing skeletal muscle mitochondrial content), the effects of social jetlag on exercise training adaptations have yet to be shown. PURPOSE: To determine how social jetlag impacts skeletal muscle adaptations to exercise training in mice. METHODS: Male C57BL/6J mice aged 10-weeks (n=40) were assigned to four groups, with experimental conditions persisting for 6-weeks; control sedentary (C-SED), control with voluntary wheel exercise (C-EX), social jetlag sedentary (SJL-SED), and social jetlag with exercise (SJL-EX). SJL was introduced weekly via 4h shifts in light/dark cycles on weekends. Skeletal muscles (quad, gas, sol) were collected for gravimetric analysis, and assessment of circadian clock gene expression and mitochondrial content. RESULTS: Mice with SJL had larger quadriceps (ME-SJL, p\u3c0.05), but this effect was lost when normalized to BW. Exercised mice had smaller quadriceps (ME-EX, p\u3c0.05), and larger solei (ME-EX, p\u3c0.05). No effects of SJL were seen in solei. SJL led to alterations in PER1, PER2, and CRY2 expression (ME-SJL, p\u3c0.05 all), while exercise led to reductions in PER2 and CRY2 expression (ME-EX, p\u3c0.05), with no interactions reaching significance. Exercise increased OXPHOS complex expression (ME Exercise; C-V, C-III, C-I, all p\u3c0.05), which was attenuated by SJL (ME SJL; C-II, C-I, p\u3c0.05). We found an interaction in C-IV expression where the exercise-induced increase was blunted in SJL-EX mice (p\u3c0.05). CONCLUSION: These data suggest that, while exercise has a beneficial impact on mitochondrial content in skeletal muscle, social jetlag prevents some of the exercise-induced improvements, potentially via disruption of the muscle circadian clock

Effects of Chronotype and Social Jetlag on Blood Biomarkers During WLFF 2-Week Critical Training Period

Chronotype, an individual\u27s natural preference towards activity during certain times of the day, influences the interaction between one\u27s internal circadian rhythms and the external environment. When this is disrupted, it can result in social jet lag (SJL), the misalignment between our sleep/wake schedule on work days and free days. Wildland firefighters grapple with unpredictable and intense demands of their job, making them vulnerable to the challenges posed by SJL. Their duties necessitate abrupt changes in active hours, pushing against their body\u27s inherent circadian preferences. SJL is a behavioral trait that may alter an individual\u27s ability to respond to high stress environments and situations. PURPOSE: To analyze the relationship between chronotype and social jet lag on blood biomarkers during a WLFF 2-week Critical Training period. METHODS: Participants underwent baseline testing which included the Morningness-Eveningness Questionnaire and the Munich Chronotype Questionnaire. Anthropometric measurements were recorded alongside body composition via skinfold measurements. A comprehensive blood draw was conducted to analyze Complete Blood Count. Following baseline assessments, participants entered a 12-day CT period. During this period, daily activity and HR were monitored. Participants maintained a daily training log, sleep log, and completed a Visual Analog Scale for sleep quality and muscle soreness. Upon completion of the CT period, the same measurements as the baseline testing were completed. RESULTS: 25 participants completed the study. Chronotype analysis showed a ME of exercise in lactate dehydrogenase (LDH) and creatine kinase (CK) with both increasing post-CT in intermediate (INT) and morning-types (MT) (p1h of SJL (pCONCLUSION: This data shows that chronotype and SJL had modest effects on blood biomarkers in response to a 2-week CT period but the magnitude of SJL does influence the increase in muscle damage biomarkers. Strategies to mitigate SJL among WLFFs may be necessary to manage the effects of hard training