Force capacity of trunk muscle extension and flexion in healthy inactive, endurance and strength-trained subjects—a pilot study

Abstract

Recreational sports are becoming increasingly important in overcoming the drawbacks of our modern sedentary lifestyle. We wanted to know whether ambitious strength or endurance training has a systematic effect on the maximum strength capacity of the trunk muscles compared to no sport at all. We investigated two groups of physically active men who practised either endurance (ET; cycling and triathlon, n = 13) or strength training (ST; power lifting, n = 13), and a group of healthy physically inactive men (control [C], n = 12). Training intensity was at competition level in both active groups. All participants performed isometric maximum voluntary contractions in flexion and extension direction. Independent of force direction maximum torque levels were highest for the ST group (p < 0.001 vs. ET and C), but after normalizing to the subject’s upper body weight these differences decreased, together with a drop in significance levels (extension: p < 0.01 vs. C; flexion: p < 0.05 vs. ET; p < 0.01 vs. C). With respect to the ratio between extension and flexion maximum forces due to the small group size no systematic differences could be detected between the groups, but effect sizes imply relevant effects (ET vs. ST: d = 0.588, ST vs C: d = −0.811). The results of this pilot study indicate that ST show higher functional force capacity values for flexion compared to the other groups. For extension, ST and ET did not differ. These results imply relevant differences for the extension to flexion force ratio.