Mechanical overload and skeletal muscle fiber hyperplasia: a meta
-analysis.
George, Dr., Kelley.
Department of Physical Education, Northern Illinois University
APStracts 3:0262A, 1996.
Using the meta-analytic approach, the purpose of this study was to
examine the effects of mechanical overload on skeletal muscle fiber
number in animals. A total of 17 studies yielding 37 data points and
360 subjects met the initial inclusion criteria: (1) "basic"
research studies published in journals, (2) animals (no humans) as
subjects, (3) control group included, (4) some type of mechanical
overload (stretch, exercise, or compensatory hypertrophy) used to
induce changes in muscle fiber number, and (5) sufficient data to
accurately calculate percent changes in muscle fiber number. Across
all designs and categories, statistically significant increases were
found for muscle fiber number (mean + SD = 15.00 + 19.60%, 95%
confidence interval = 8.65 to 21.53), muscle fiber area (mean + SD =
31.60 + 44.30%, 95% confidence interval = 16.83 to 46.37) and muscle
mass (mean + SD = 90.50 + 86.50%, 95% confidence interval = 61.59 to
119.34). When partitioned according to fiber counting technique,
larger increases in muscle fiber number were found using the
histological versus nitric acid digestion method (histological =
20.70%, nitric acid digestion = 11.10%, p = .14). Increases in fiber
number partitioned according to species were greatest among those
groups which used an avian versus mammalian model (avian = 20.95%,
mammalian = 7.97%, p = .07). Stretch overload yielded larger
increases in muscle fiber number than exercise and compensatory
hypertrophy (stretch = 20.95%, exercise = 11.59%, compensatory
hypertrophy = 5.44%, p = .06). No significant differences between
changes in fiber number were found when data were partitioned
according to type of control (intra-animal = 15.20%, between animal =
13.90%, p = .82), or fiber arrangement of muscle (parallel = 15.80%,
pennate = 11.60%, p = .61). The results of this study suggest that in
several animal species certain forms of mechanical overload increase
muscle fiber number.
Received 26 Febrary 1996; accepted in final form 15 February
1996.
APS Manuscript Number A187-6.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 June 96