Changes in strength and cross sectional area of the elbow flexors as a result of isometric strength training

Abstract

Changes in strength and size of the elbow flexor muscles have been compared during six weeks of isometric strength training in six male and six female subjects. Isometric training of one arm resulted in a significant increase in isometric force (14.5 +/- 5.1%, mean +/- SD, n = 12). No differences were seen in the response of male and female subjects. The extent of the change was similar to that reported for training studies of other muscles, thus refuting the suggestion that the elbow flexors may be especially amenable to training. Biceps and brachialis cross-sectional area (CSA) was measured from mid-upper arm X-ray computerized tomography before and after training. Muscles increased in area (5.4 +/- 3.8%) but this was smaller than, and not correlated with, the increase in strength. The main change in the first six weeks of strength training was therefore an increase in the force generated per unit cross-sectional area of muscle. The arrangement of fibres in the biceps is nearly parallel to the action of the muscle and it is argued that the increase in force per unit cross-sectional area is unlikely to be due to changes in the pennation of the muscle fibres as has been suggested for other muscles.

Changes in agonist neural drive, hypertrophy and pre-training strength all contribute to the individual strength gains after resistance training

“…QUADS VOL total quadriceps muscle volume, QEMG MVT quadriceps EMG measured during MVT production earlier studies did not find a relationship between hypertrophy and strength gains, they involved smaller cohorts (≤12) or less precise measurements of muscle size (e.g. single slice scans; Jones and Rutherford 1987;Davies et al 1988). The simple comparison of group level changes in MVT (+21.7%) and QUADS VOL (+5.6%) suggest that muscle hypertrophy accounts for at most 25% of the change in strength following isometric knee extensor RT over 12 weeks.…”

Assessing Voluntary Muscle Activation with the Twitch Interpolation Technique

“…Three factors should be borne in mind when interpreting the available evidence. Firstly, in a number of the earlier studies voluntary activation of the elbow flexors [7,95] and quadriceps femoris muscles [8,96,97] appeared to be complete prior to training although subsequent experiments employing more sensitive techniques have shown that the same muscles are typically not fully activated [14,15,17,21,66,73] . Secondly, when activation deficits have been observed, dynamic resistance training was employed whilst the tests of voluntary activation were isometric [71,98] .…”

“…Most twitch interpolation studies employing healthy adult subjects suggest that voluntary activation does not increase after resistance training [7,8,66,71,95,96,97,98] , although there are exceptions [31,68,99] . Three factors should be borne in mind when interpreting the available evidence.…”

“…1,4,5,6,7,8,9,10,11,12] . However, the methods employed in these early studies were not particularly sensitive and higher resolution techniques [eg.…”

“…The original twitch interpolation technique described by Merton [3] and subsequently employed by many others [1,5,6,7,8,9,12,14,29] involved a single stimulus interpolated over voluntary contractions. Recently it has become common for 2 or more stimuli (50-100 Hz) to be employed [17,18,34,38,51] because the evoked force increments are larger and more readily detected [15,32,43,45,54,55,56,57,58] .…”