Functional and structural adaptations in skeletal muscle of trained athletes.
Twitch contractile and ultrastructural characteristics of the human triceps surae were determined in six male strength-trained athletes, six endurance-trained athletes, six active controls, and seven sedentary controls of similar height and age. Twitch contraction time in the triceps surae complex was 20% longer in strength-trained and sedentary groups than in endurance-trained or active control groups. In the 15 subjects peak twitch torque and one-half relation time in the triceps surae were 22.6 +/- 7.9 N.m and 91.1 +/- 18.3 ms, respectively. Mean fiber area in the gastrocnemius was approximately 1.6-, 1.7-, and 2.5-fold greater in the active control, endurance-trained, and strength-trained groups, respectively, relative to the sedentary group. Despite these large differences in fiber areas, the fiber fractional volume of the sarcoplasmic reticulum-transverse tubule network averaged 3.38 +/- 0.86% and 5.50 +/- 0.94% in type I and type II fibers, respectively, in all subjects. The fractional fiber volume of cytoplasm and lipid were similar for all four groups. However, mitochondrial volume was approximately 30% lower in both fiber types of the strength-trained group relative to the other groups. This implies that with exercise-induced hypertrophy, the sarcoplasmic reticulum, cytoplasm, and lipid components increase proportionately with contractile protein, whereas the mitochondrial fraction does not. The proportion of type I fibers in the soleus, medial gastrocnemius, and lateral gastrocnemius was 75.2 +/- 8.3, 58.5 +/- 6.1, and 52.4 +/- 4.2%, respectively, and was similar in all subject groups. The results demonstrate that twitch duration is prolonged in strength-trained athletes relative to endurance athletes.(ABSTRACT TRUNCATED AT 250 WORDS)
Alway
S E
SE
Department of Physical Education, McMaster University, Hamilton, Ontario, Canada.
MacDougall
J D
JD
Sale
D G
DG
Sutton
J R
JR
McComas
A J
AJ
D000293:Adolescent; D000328:Adult; D006801:Humans; D008297:Male; D008854:Microscopy, Electron; D008870:Microtubules / Q000648:ultrastructure; D008931:Mitochondria, Muscle / Q000648:ultrastructure; D009119:Muscle Contraction; D009132:Muscles / Q000032:analysis / Q000502:physiology* / Q000648:ultrastructure; D005082:Physical Exertion; D012420:Running; D012519:Sarcoplasmic Reticulum / Q000648:ultrastructure*; D014891:Weight Lifting