title: Age-related differences in the properties of the plantar flexor muscles and tendons.
abstract: OBJECTIVE
  The purpose of this study was to determine age-related differences in the human plantar flexor muscles and tendon.
  
  
  METHODS
  Four age groups--a 20-yr group (20-27 yr, N = 19), 30-yr group (31-38 yr, N = 15), 50-yr group (46-57 yr, N = 10) and 70-yr group (62-77 yr, N = 15)--volunteered to take part in the present study. Muscle thickness, strength, and activation level (using twitch-interpolation technique) of plantar flexor muscles were measured. Elongation of the Achilles tendon was determined using ultrasonography while subjects performed ramp isometric plantar flexion up to the voluntary maximum.
  
  
  RESULTS
  No significant difference in relative muscle thickness (to limb length) was observed among the four age groups. Muscle strength and activation level of the 20-yr group were significantly higher than those of the 50- and 70-yr groups (activation levels were not measured in the 70-yr group), and maximal strain (elongation/initial tendon length) of the Achilles tendon decreased with aging. Although there were no differences in muscle strength and activation levels between the 20- and 30-yr groups, maximal strain of the Achilles tendon of the 30-yr group was already lower than that of the 20-yr group (P = 0.062).
  
  
  CONCLUSIONS
  These results suggest that the processes of age-related changes in the muscle and tendon are different. Furthermore, the differences in age-related changes of muscle and tendon might play a role in the frequency of Achilles tendon ruptures among men in their 30s.
authors.affiliation: Department of Life Science, University of Tokyo, Meguro, Tokyo, Japan. kubo@idaten.c.u-tokyo.ac.jp
authors.forename: Keitaro
authors.initials: K
authors.lastname: Kubo
authors.forename: Masanori
authors.initials: M
authors.lastname: Morimoto
authors.forename: Teruaki
authors.initials: T
authors.lastname: Komuro
authors.forename: Naoya
authors.initials: N
authors.lastname: Tsunoda
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Kanehisa
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Fukunaga
mesh_terms: D000125:Achilles Tendon / Q000000981:diagnostic imaging / Q000293:injuries / Q000502:physiology*; D000328:Adult; D000367:Age Factors; D000368:Aged; D000375:Aging / Q000502:physiology*; D005528:Foot / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology*; D053580:Muscle Strength / Q000502:physiology*; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging / Q000502:physiology*; D010865:Pilot Projects; D013314:Stress, Mechanical; D013708:Tendon Injuries / Q000209:etiology*; D014463:Ultrasonography