Effects of High-Intensity Interval Training and Isoinertial Training on Leg Extensors Muscle Function, Structure, and Intermuscular Adipose Tissue in Older Adults.

We compared the effects of aerobic high-intensity training () and isoinertial resistance training () on the strength, mass, architecture, intermuscular adipose tissue () quality, and neuromuscular activation of the quadriceps in elderly subjects. Twelve healthy men (69.3 ± 4.2 years; 77.8 ± 10.4 kg; 1.72 ± 0.05 m) were exposed to 8 weeks of (7 × 2-min cycling repetitions at 90% of O , 3 times/week) and, after 4 months (detraining), to (4 × 7 maximal concentric-eccentric knee extensions, 3 times/week). Before and after trainings, we measured knee extension isometric ( ) and dynamic ( ) maximal concentric torque, anatomical cross-sectional area () at 25, 50, and 75% of femur length, quadriceps volume (), , pennation angle (θ ) of the fibers from the , and voluntary activation (). and were significantly larger only after ( = 0.008); was able to elicit a greater increase of than ; increases similarly and significantly after and ( = 0.003-0.001); at 50% of femur length decreased after both and ( = 0.001-0.003); physiological cross-sectional area () was larger after than before ( = 0.025); specific torque did not change throughout the study (45.5 N cm ± 12.0); % of the quadriceps was significantly affected only by ( = 0.011). Both and are able to elicit beneficial modifications of muscular mass, architecture, and quality (reducing ) in elderly subjects in connection with an amelioration of strength. and caused a homogeneous increase of and of of the quadriceps. increases, but specific strength per unit of did not change. The increases of functional torque seemed to be attributed to a parallel increase of % and muscle hypertrophy only after . Data suggest that may be a prominent indicator to track metabolic-dependent activity and skeletal muscle quality.