title: Muscle inactivity is adversely associated with biomarkers in physically active adults.
abstract: OBJECTIVE
  While the lack of muscular activity is a proposed trigger for metabolic alterations, this association has not been directly measured. We examined the associations between EMG-derived muscle inactivity and activity patterns and cardiometabolic biomarkers in healthy, physically active adults.
  
  
  METHODS
  Data for this cross-sectional study were pooled from two studies (EMG24 and InPact), resulting in a sample of 150 individuals without known chronic diseases and with high-quality EMG data (female n = 85, male n = 65, age = 38.8 ± 10.6 yr, body mass index = 23.8 ± 3.1 kg·m⁻²). EMG was measured during one to three typical weekdays using EMG shorts, measuring quadriceps and hamstring muscle EMG. Muscle inactivity time and moderate- to vigorous-intensity muscle activity were defined as EMG amplitude below that of standing still and above that of walking 5 km·h⁻¹, respectively. Blood pressure index, waist circumference, fasting plasma glucose, HDL cholesterol, and triglycerides were measured, and long-term exercise behaviors were assessed by questionnaire.
  
  
  RESULTS
  In a group of physically active participants, muscles were inactive for 65.2% ± 12.9% of the measurement time in an average of 24.1 ± 9.8-s periods. Compared to those in the lowest muscle inactivity quartile (<55.5% of measurement time), those in the highest quartile (≥74.8% of measurement time) had 0.32 mmol·L⁻¹ lower HDL cholesterol (P < 0.05) and 0.30 mM higher triglycerides (P < 0.05) independent of muscle's moderate- to vigorous-intensity activity.
  
  
  CONCLUSIONS
  Clinically significant differences in HDL cholesterol and triglycerides were found, favoring participants having low muscle inactivity time, independent of moderate- to vigorous-intensity muscle activity. Even physically active individuals may benefit from light-intensity activities that reduce ubiquitous muscle inactivity time.
authors.affiliation: 1Department of Biology of Physical Activity, Neuromuscular Research Center, University of Jyväskylä, FINLAND; 2Department of Sport Sciences, University of Jyväskylä, FINLAND; and 3Department of Health Sciences, Gerontology Research Center, University of Jyväskylä, FINLAND.
authors.forename: Arto J
authors.initials: AJ
authors.lastname: Pesola
authors.forename: Arto
authors.initials: A
authors.lastname: Laukkanen
authors.forename: Olli
authors.initials: O
authors.lastname: Tikkanen
authors.forename: Sarianna
authors.initials: S
authors.lastname: Sipilä
authors.forename: Heikki
authors.initials: H
authors.lastname: Kainulainen
authors.forename: Taija
authors.initials: T
authors.lastname: Finni
mesh_terms: D000203:Activities of Daily Living; D000328:Adult; D000368:Aged; D000886:Anthropometry; D015415:Biomarkers / Q000097:blood; D008076:Cholesterol, HDL / Q000097:blood*; D003430:Cross-Sectional Studies; D004576:Electromyography; D004734:Energy Metabolism / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000502:physiology*; D057185:Sedentary Behavior; D014280:Triglycerides / Q000097:blood*
chemical_list: D015415:Biomarkers; D008076:Cholesterol, HDL; D014280:Triglycerides