title: The reduction of physical activity reflects on the bone mass among young females: a follow-up study of 142 adolescent girls.
abstract: Maintenance of positive effects of physical activity on growing bone is unknown. Physical activity was associated with increased BMC and BMD in a 7-year follow-up with 142 adolescent girls. Marked reduction in physical activity had an unfavorable effect on bone measurements, which is an important finding when the prevention of osteoporosis is considered.
  
  
  BACKGROUND
  Environmental factors influence quality and durability of bone. Physical activity, with high-impact weight bearing activity during puberty in particular, has been shown to have a beneficial effect on growing bone. Only few studies have been published on the maintenance of these effects.
  
  
  METHODS
  At baseline, 142 girls aged 9-15 years participated in the present 7-year follow-up study. Growth and development, physical activity, and intakes of calcium and vitamin-D were recorded at intervals. BMC and BMD measurements were repeated using DXA. Based on the recording of physical activity during the follow-up measurements, the effect of the reduction in physical activity was examined with the bone measurements, and the measurements in the tertiles based on the amount of physical activity during the whole follow-up period were compared.
  
  
  RESULTS
  Physical activity was positively associated with the development of BMC and BMD during the follow-up. The mean BMC of the lumbar spine increased 1.69 g (3%) (p = 0.021) more among those girls who maintained the physical activity level as compared with those who reduced it during last 4 years. In the femoral neck, the corresponding difference was 0.14 g (4.6%) (p = 0.015) between the same two groups of girls. The mean increases in BMC at lumbar spine and femoral neck were more substantial among those girls having the highest physical activity levels during the 7-year follow-up (46.7% and 22.6%) as compared with those having the lowest physical activity levels (43.3% and 17.4%, respectively).
  
  
  CONCLUSIONS
  The findings of the present study show that regular physical activity is valuable in preserving the peak bone mass acquired at puberty in particular. Many of the girls who markedly reduced their activity levels lost bone in their femoral neck prior to their 25th birthday.
authors.affiliation: Jyväskylä Central Hospital, Keskussairaalantie 19, 40620, Jyväskylä, Finland. esanra@utu.fi
authors.forename: E
authors.initials: E
authors.lastname: Rautava
authors.forename: M
authors.initials: M
authors.lastname: Lehtonen-Veromaa
authors.forename: H
authors.initials: H
authors.lastname: Kautiainen
authors.forename: S
authors.initials: S
authors.lastname: Kajander
authors.forename: O J
authors.initials: OJ
authors.lastname: Heinonen
authors.forename: J
authors.initials: J
authors.lastname: Viikari
authors.forename: T
authors.initials: T
authors.lastname: Möttönen
mesh_terms: D015502:Absorptiometry, Photon; D000293:Adolescent; D015519:Bone Density / Q000502:physiology*; D001846:Bone Development / Q000502:physiology*; D001842:Bone and Bones / Q000000981:diagnostic imaging / Q000502:physiology*; D002648:Child; D015444:Exercise / Q000502:physiology*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D009043:Motor Activity / Q000502:physiology*; D010024:Osteoporosis / Q000517:prevention & control