Weekly versus monthly testosterone administration on fast and slow skeletal muscle fibers in older adult males.
BACKGROUND
In older adults, loss of mobility due to sarcopenia is exacerbated in men with low serum T. T replacement therapy is known to increase muscle mass and strength, but the effect of weekly (WK) vs monthly (MO) administration on specific fiber types is unknown.


OBJECTIVE
To determine the efficacy of WK vs MO T replacement on the size and functional capacity of individual fast and slow skeletal muscle fiber types.


METHODS
Subjects were randomized into a 5-month, double-blind, placebo-controlled trial. All subjects (ages, 61-71 y) were community-dwelling men who had T levels < 500 ng/dL.


METHODS
Subjects were dosed weekly for 5 months, receiving continuous T (WK, n = 5; 100 mg T enanthate, im injection), monthly cycled T (MO, n = 7; alternating months of T and placebo), or placebo (n = 7). Muscle biopsies of the vastus lateralis were obtained before and after treatment.


METHODS
Main outcomes for individual slow and fast fibers included fiber diameter, peak force (P0), rate of tension development, maximal shortening velocity, peak power, and Ca(2+) sensitivity.


RESULTS
Both treatments increased fiber diameter and peak power, with WK treatment 5-fold more effective than MO in increasing type I fiber P0. WK effects on fiber diameter and force were 1.5-fold higher in slow fibers compared to fast fibers. In fast type II fibers, diameter and P0 increased similarly between treatments. The increased power was entirely due to increased fiber size and force.


CONCLUSIONS
In conclusion, T replacement effects were fiber-type dependent, restricted to increases in cell size, P0, and peak power, and dependent on the paradigm selected (WK vs MO).
Department of Biological Sciences (R.H.F., J.R.P.), Marquette University, Milwaukee, Wisconsin 53233; and Department of Internal Medicine (E.L.D., W.J.D., M.S.-M., R.J.U.), University of Texas Medical Branch at Galveston, Texas 77555.
Robert H
RH
Fitts
James R
JR
Peters
E Lichar
EL
Dillon
William J
WJ
Durham
Melinda
M
Sheffield-Moore
Randall J
RJ
Urban
D000368:Aged; D004311:Double-Blind Method; D004334:Drug Administration Schedule; D020249:Hormone Replacement Therapy / Q000379:methods*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000187:drug effects; D018656:Muscle Fibers, Fast-Twitch / Q000187:drug effects*; D018657:Muscle Fibers, Slow-Twitch / Q000187:drug effects*; D055948:Sarcopenia / Q000188:drug therapy*; D013739:Testosterone / Q000008:administration & dosage* / Q000627:therapeutic use; D016896:Treatment Outcome
D013739:Testosterone