title: Effect of age on metabolic fatigue and on indirect symptoms of skeletal muscle damage after stretch-shortening exercise.
abstract: OBJECTIVE
  The purpose of this study was to establish the main differences between men (M) and adolescents (A) (males) in metabolic fatigue and damage induced by exercise performed at maximal intensity.
  
  
  METHODS
  Healthy A (age 13.4 0.6 years, n = 12) and healthy adult M (age 25.4 1.7 years, n = 12) participated in this study. To induce muscle damage and metabolic fatigue stretch-shortening exercise (SSE) (5 bouts of 20 jumps with counter-movement to 90 degrees angle in the knee with 10 s between bouts) has been chosen. The following data were measured: the force of the quadriceps muscle, aroused by electrical stimulation at different frequencies, maximal voluntary contraction force, height of jump (JH), muscle soreness, lactate (La) concentration and creatine kinase (CK) activity in the blood. All the parameters mentioned were measured before exercise and 2-5 min, 20 min, 24 h and 48 h after the SSE, except for La concentration changes in the blood measured before exercise, 2 min and 20 min after the SSE.
  
  
  RESULTS
  The main findings in this study are the following: 1) during SSE JH decreased significantly (P < 0.05) more in M than in A, whereas La concentration in the blood after SSE increased more in M than in A; 2) indirect symptoms of muscle damage were more evident in M than in A; 3) there was secondary decrease in electrically induced muscle force at 10-20 Hz from 3 min until 20 min after SSE but only in the muscles of M; 4) low frequency fatigue after SSE was more evident in M than A.
  
  
  CONCLUSIONS
  The results of the present study indicate that the muscles of adolescents are more resistant to both metabolic fatigue and exercise-induced damage than those of men.
authors.affiliation: Laboratory of Human Motorics, Department of Applied Physiology and Health Education, Lithuanian Academy of Physical Education, Kaunas, Lithuania. a.skurvydas@lkka.lt
authors.forename: A
authors.initials: A
authors.lastname: Skurvydas
authors.forename: V
authors.initials: V
authors.lastname: Streckis
authors.forename: D
authors.initials: D
authors.lastname: Mickeviciene
authors.forename: S
authors.initials: S
authors.lastname: Kamandulis
authors.forename: A
authors.initials: A
authors.lastname: Stanislovaitis
authors.forename: G
authors.initials: G
authors.lastname: Mamkus
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000704:Analysis of Variance; D015415:Biomarkers / Q000097:blood; D003402:Creatine Kinase / Q000097:blood; D004558:Electric Stimulation; D004734:Energy Metabolism; D015444:Exercise; D006801:Humans; D019344:Lactic Acid / Q000097:blood; D008297:Male; D009068:Movement; D009119:Muscle Contraction; D018763:Muscle Fatigue; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000503:physiopathology*; D010807:Physical Endurance; D012016:Reference Values
chemical_list: D015415:Biomarkers; D019344:Lactic Acid; D003402:Creatine Kinase