The Effects of Varying Glenohumeral Joint Angle on Acute Volume Load, Muscle Activation, Swelling, and Echo-Intensity on the Biceps Brachii in Resistance-Trained Individuals

Abstract

There is a paucity of data on how manipulating joint angles during isolation exercises may impact overall session muscle activation and volume load in resistance-trained individuals. We investigated the acute effects of varying glenohumeral joint angle on the biceps brachii with a crossover repeated measure design with three different biceps curls. One session served as the positive control (CON), which subjects performed 9 sets of bicep curls with their shoulder in a neutral position. The experimental condition (VAR), varied the glenohumeral joint angle by performing 3 sets in shoulder extension (30°), 3 sets neutral (0°), and 3 sets in flexion (90°). Volume load and muscle activation (EMG) were recorded during the training sessions. Muscle swelling and strain were assessed via muscle thickness and echo-intensity responses at pre, post, 24 h, 48 h, and 72 h. There were no significant differences between conditions for most dependent variables. However, the overall session EMG amplitude was significantly higher (p = 0.0001) in VAR compared to CON condition (95%-CI: 8.4% to 23.3%). Our findings suggest that varying joint angles during resistance training (RT) may enhance total muscle activation without negatively affecting volume load within a training session in resistance-trained individuals.

Keywords: bodybuilding; echo-intensity; exercise selection; muscle length-tension relationship; muscle strain.

Figure 1

Glenohumeral joint angles—(A) -30° extension, lengthened; (B) 0°, neutral; (C) 90° flexion, shortened. Please confirm which form of degree you want to use: degree or the unit “°” and please use the same form for unification in the main text.

Figure 2

Mid-belly (37.5%) location site utilized for electrode placement, muscle thickness, and echo-intensity assessments.

Figure 3

Total session volume load (A) and overall session surface electromyography (root mean square % of maximum isometric voluntary contraction) (B).

Figure 4

Muscle thickness (i.e., swelling) individual responses for changes at the 25% (distal) and 37.5% (mid-belly) landmarks from pre to post, 24, 48, and 72 h workout.

Figure 5

Echo-intensity individual responses for changes at the 25% (distal) and 37.5% (mid-belly) landmarks from pre to post, 24, 48, and 72 h workout.