Resistance training is widely prescribed for rehabilitation of injuries and as a
method to improve athletic performance. It is accepted that resistance training
increases the maximal force production of whole muscle and it has been suggested that
the velocity of shortening can increase as well. However, little is known about the
effects of resistance training at the cellular level. Therefore, we investigated
morphology, force production, velocity, and force-velocity-power relationships of
single chemically skinned muscle fibers from chronically resistance trained humans,
including cross sectional area (CSA), peak Ca²⁺ -activated force production (P₀),
specific tension (P₀/CSA), unloaded shortening velocity (V₀), and isotonic
contractions. The untrained group (NT) group consisted of sedentary males (n=6, age
=27 ± 2 yrs) while the chronically trained group (CHRT) group consisted of males
with 7.7 ± 0.4 yrs resistance training experience (n=6, 22 ± 1 yrs). Maximum
voluntary isometric and isokinetic knee extensor strength were measured along with 6
repetition maximum (6RM) free weight bench press and leg press. Muscle biopsies
were obtained from the vastus lateralis. Chemically skinned single muscle fibers were
mounted between a force transducer and servo-controlled motor and subjected to slack
tests to determine peak Ca²⁺ -activated force (P₀) and unloaded shortening velocity
(V₀). Isotonic load clamps were used to determine the force-velocity-power
relationship. All fiber experiments were performed at 15°C. Fiber myosin heavy
chain (MHC) content was determined by gel electrophoresis. The CHRT group was
119% and 81% stronger for 6RM leg press and bench press respectively. Peak
isometric torque was 28% greater for the CHRT subjects and was significantly higher
at all isokinetic speeds tested. No differences were seen in strength or isokinetic power
between groups after normalization for lean body mass. CHRT fibers (n=213)
expressing type I, IIa, and I₀a/IIx MHC were significantly greater in CSA (+41%,
+51%, and +33%, respectively) and produced significantly greater P₀ (+37%, +48%,
and +34%, respectively) than NT fibers (n=236). However, P₀/CSA was not different
between CHRT and NT groups. Fibers expressing type IIa/IIx fibers produced greater
P₀/CSA than IIa which produced greater P₀/CSA than type I. The P₀/CSA
relationship between fibers within groups was type IIa/IIx>IIa>I and was significant
for both groups. Fiber V₀ was not different between groups. Absolute power was
significantly greater in the CHRT for all fiber types whereas power normalized for
fiber volume was not different between groups. This resulted in a significantly greater
force at peak power for all but type IIa/IIx fibers and trends for greater velocity at
peak power. Single-cell contractile function in terms of V₀ and P₀/CSA, measured
under standardized conditions, appears to be unaltered as a result of long term CHRT
in young adult males. Group differences in absolute P₀ can be attributed solely to the
greater CSA of the CHRT fibers. Long-term CHRT is not associated with a difference
in fiber V₀. Therefore, the greater power was due entirely to the greater force. These
data suggest that differences in whole muscle strength and power between NT and
CHRT groups are primarily due to differences in fiber CSA rather than differences in
cross-bridge mechanisms of contraction. Supported by National Institute of Health
grant R3AR46392A. / Graduation date: 2002
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/29965 |
| Date | 06 August 2001 |
| Creators | Shoepe, Todd C. |
| Contributors | Widrick, Jeffrey J. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
Page generated in 0.0019 seconds