AUTHOR=Bruseghini Paolo , Capelli Carlo , Calabria Elisa , Rossi Andrea P. , Tam Enrico 

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

JOURNAL=Frontiers in Physiology

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2019.01260

DOI=10.3389/fphys.2019.01260

ISSN=1664-042X

ABSTRACT=<p>We compared the effects of aerobic high-intensity training (<italic>HIT</italic>) and isoinertial resistance training (<italic>IRT</italic>) on the strength, mass, architecture, intermuscular adipose tissue (<italic>IMAT</italic>) 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 <italic>HIT</italic> (7 × 2-min cycling repetitions at 90% of <inline-formula><mml:math id="INEQ1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mover accent="true"><mml:mi>V</mml:mi><mml:mo>.</mml:mo></mml:mover></mml:math></inline-formula>O<sub>2</sub><sub>peak</sub>, 3 times/week) and, after 4 months (detraining), to <italic>IRT</italic> (4 × 7 maximal concentric–eccentric knee extensions, 3 times/week). Before and after trainings, we measured knee extension isometric (<italic>T</italic><sub>MVC</sub>) and dynamic (<italic>T</italic><sub>C</sub>) maximal concentric torque, anatomical cross-sectional area (<italic>ACSA</italic>) at 25, 50, and 75% of femur length, quadriceps volume (<italic>Vol</italic>), <italic>IMAT</italic>, pennation angle (θ<italic><sub>p</sub></italic>) of the fibers from the <italic>vastus lateralis</italic>, and voluntary activation (<italic>%Act</italic>). <italic>T</italic><sub>MVC</sub> and <italic>T</italic><sub>C</sub> were significantly larger only after <italic>IRT</italic> (<italic>P</italic> = 0.008); <italic>IRT</italic> was able to elicit a greater increase of <italic>ACSA</italic> than <italic>HIT</italic>; <italic>Vol</italic> increases similarly and significantly after <italic>HIT</italic> and <italic>IRT</italic> (<italic>P</italic> = 0.003–0.001); <italic>IMAT</italic> at 50% of femur length decreased after both <italic>HIT</italic> and <italic>IRT</italic> (<italic>P</italic> = 0.001–0.003); physiological cross-sectional area (<italic>PCSA</italic>) was larger after <italic>IRT</italic> than before (<italic>P</italic> = 0.025); specific torque did not change throughout the study (45.5 N cm<sup>–2</sup> ± 12.0); %<italic>Act</italic> of the quadriceps was significantly affected only by <italic>IRT</italic> (<italic>P</italic> = 0.011). Both <italic>HIT</italic> and <italic>IRT</italic> are able to elicit beneficial modifications of muscular mass, architecture, and quality (reducing <italic>IMAT</italic>) in elderly subjects in connection with an amelioration of strength. <italic>HIT</italic> and <italic>IRT</italic> caused a homogeneous increase of <italic>ACSA</italic> and of <italic>Vol</italic> of the quadriceps. <italic>PCSA</italic> increases, but specific strength per unit of <italic>PCSA</italic> did not change. The increases of functional torque seemed to be attributed to a parallel increase of %<italic>Act</italic> and muscle hypertrophy only after <italic>IRT</italic>. Data suggest that <italic>IMAT</italic> may be a prominent indicator to track metabolic-dependent activity and skeletal muscle quality.</p>