Introduction and Objectives: Neuromuscular control of the rectus abdominis (RA), obliquus internus (OI), obliquus externus (OE), and erector spinae (ES) muscles has been widely investigated during a range of conditions such as perturbations , stability exercises , gait  and other functional exercises  using electromyography (EMG). However, little attention has been paid to activity of these muscles during spinal range of motion exercises, in particular in a 4-point kneeling posture (4P), even though this posture is often adopted for low back pain exercises. The aim of this study was to investigate the concentric and eccentric activity of trunk muscles during active spinal range of motion exercises in young and mature healthy adults in two postures.
Methods: Twenty-four healthy participants (12 young, aged 18-25 years; 12 mature, aged 45-60 years) were included. Reflective markers were attached over the spinous process of the 11th thoracic vertebra (T11), the head, the left and right styloid processes, and lateral femoral condyles. Three-dimensional kinematic data were collected using 10 high speed cameras (Eagle Digital Real Time System, Motion Analysis Corp., 120Hz). Surface EMG electrodes (Delsys Trigno, 1200Hz) were attached over the left and right ES, RA, OE, and OI after skin preparation. Data were collected during three repetitions of 10s of flexion and extension movements in U and 4P. Participants were instructed to perform each movement to their end range and return to the starting posture in one fluent movement. Raw EMG data were resampled, rectified, zero-mean offset, and a 4th order low pass Butterworth filter applied. Processed EMG data from 0.5s before movement onset and 0.5s after movement cessation (both based on vertical T11 movement) were included for analysis. EMG data were normalised to the maximally observed muscle activity from any trial and movement for each muscle, and the maximum and 1st, 2nd, and 3rd quartiles (Q1, Q2, Q3) calculated for the concentric and eccentric phase of muscle activity. Due to non-normally distributed data, differences between concentric and eccentric activity were compared for Q1, Q2 and Q3 in the young and mature groups separately using a Wilcoxon Rank test.
Results: Significant differences were found for every muscle and quartile, although this was dependant on age group, posture adopted and movement direction. Where significant differences occurred in 4P, concentric activity was greater than eccentric activity for flexion and extension in both the young group (flexion: RA left 01, all abdominal muscles Q2 and Q3; extension: ES Q2 and Q3, RA and OE left Q1 and Q2, Q1 all quartiles; all p<0.05) and mature group (flexion: ES left all quartiles, ES right 01, all abdominals Q3, RA right and Q1 left Q2, extension: ES Q2 and Q3, Q1 and OE Q1 and Q2, Q1 right Q3; all p<0.05). However, for both age groups in U during flexion, concentric activity was significantly greater than eccentric activity for ES in all quartiles, but eccentric activity was significantly greater than concentric activity in the abdominal muscles (young group: OE left Q1 , Q1 right all quartiles; mature group: OE left Q1 and Q2, OE right Q2 and Q3, QI left all quartiles; all p<0.05). The opposite was found for extension, where eccentric activity was significantly greater than concentric activity for ES but only in the young group (all quartiles; p<0.05), and concentric activity was significantly greater than eccentric activity in the abdominal muscles (young group: OE left Q3, OI Q1 and Q3; mature group: RA Q3, OE and OI left Q1, OE right and OI Q3; all p<0.05).
Conclusion: Muscle activity is generally larger during concentric than during eccentric muscle use . However, the overall findings from this study would indicate that antagonist muscle activity is usually greater during the concentric phase and agonist muscle activity is greater during the eccentric phase during active range of motion exercises in U. This is in contrast with 4P, where concentric muscle activity was greater than eccentric activity in both agonists and antagonists. These findings were identified in both age groups. Probably the effect of gravity in U reduces the need for concentric activity during active range of motion exercises and the eccentric activity, which provides control and deceleration during approach of the neutral posture, plays a more important role. The results of this study may be of relevance when selecting range of motion exercises in a low back pain rehabilitation setting.
Valentin, S., & Licka, T. (2015, July). Movement control during active spinal range of motion is achieved by a differential use of eccentric and concentric muscle activity. Paper presented at XXV Congress of the International Society of Biomechanics (ISB 2015 Glasgow), Glasgow