Trunk muscle activation during movement with a new exercise device for lumbo-pelvic reconditioning

Abstract

Gravitational unloading leads to adaptations of the human body, including the spine and its adjacent structures, making it more vulnerable to injury and pain. The Functional Re-adaptive Exercise Device (FRED) has been developed to activate the deep spinal muscles, lumbar multifidus (LM) and transversus abdominis (TrA), that provide inter-segmental control and spinal protection. The FRED provides an unstable base of support and combines weight bearing in up-right posture with side alternating, elliptical leg movements, without any resistance to movement. The present study investigated the activation of LM, TrA, obliquus externus (OE), obliquus internus (OI), abdominis, and erector spinae (ES) during FRED exercise using intramuscular fine-wire and surface EMG Nine healthy male volunteers (27 ± 5 years) have been recruited for the study. FRED exercise was compared with treadmill walking. It was confirmed that LM and TrA were continually active during FRED exercise. Compared with walking, FRED exercise resulted in similar mean activation of LM and TrA, less activation of OE, OI, ES, and greater variability of lumbo-pelvic muscle activation patterns between individual FRED/gait cycles. These data suggest that FRED continuously engages LM and TrA, and therefore, has the potential as a stationary exercise device to train these muscles.

Keywords: Deep spinal muscles; exercise device; fine‐wire electromyography; lumbar spine; rehabilitation.

Figure 1

The FRED. (A) FRED device in use. (B) Foot paths are shown for the three amplitudes investigated in this study generated using a biomechanical model of the FRED (Lindenroth et al. 2015). The plot shows that the dimensions of the ellipses increase with increasing FRED amplitudes. FRED, Functional Re‐adaptive Exercise Device.

Figure 2

Representative processed EMG curves of one participant. Intramuscular and surface EMG recordings from one participant for FRED _middle and the two gait conditions. The thick black line depicts the averaged signal of all individual cycles (thin gray lines) as calculated analyzing the last 30 sec of each task. The light dotted line at the bottom of each plot indicates the zero reference for each channel. Cycle length represents one complete revolution on the FRED or the time from heel contact to heel contact of the right foot for treadmill walking. Note that unlike the gait data that begin and end with right foot strike, data for the FRED exercise are temporally organized to a set point in the smooth foot path.

Figure 3

Mean, peak and min EMG amplitudes of the averaged EMG data. Group mean (SD) of intramuscular and surface EMG signals during the three FRED conditions (FRED _small, FRED _middle, FRED _large) and treadmill walking at natural speed (Gait_natural) and at a step frequency (0.84 Hz) matched to FRED _middle (Gait_matched). The figure shows mean (A), peak (B) and minimum (C) amplitude of the averaged curves normalized to the greatest peak activation of the averaged signal for each muscle. Intramuscular EMG–LM, lumbar multifidus; OI, obliquus internus abdominis; OE, obliquus externus abdominis; ES, erector spinae; TrA, transversus abdominis; surface EMG‐LMs, lumbar multifidus; OIs, obliquus internus abdominis; OEs, obliquus externus abdominis. *P < 0.01 and ^# P < 0.05 for pairwise comparisons.

Figure 4

Mean, peak and min amplitudes determined from individual FRED/gait cycles. (A) Mean, (B) peak, and (C) minimum EMG recorded from all recorded intramuscular and surface EMG signals from individual FRED/gait cycles. EMG amplitudes were normalizd to the greatest peak activation of the averaged signal for each muscle. Intramuscular EMG–LM, lumbar multifidus; OI, obliquus internus abdominis; OE, obliquus externus abdominis; ES, erector spinae; TrA, transversus abdominis; surface EMG‐LMs, lumbar multifidus; OIs, obliquus internus abdominis; OEs, obliquus externus abdominis. *P < 0.01 and ^# P < 0.05 for pairwise comparisons.

Figure 5

Coefficient of variation and time active. (A) The coefficient of variation indicates the variation of individual FRED/gait cycles from the averaged signal. (B) Time active indicates the percentage of time a muscle was active during the task. Intramuscular EMG–LM, lumbar multifidus; OI, obliquus internus abdominis; OE, obliquus externus abdominis; ES, erector spinae; TrA, transversus abdominis; surface EMG‐LMs, lumbar multifidus; OIs, obliquus internus abdominis; OEs, obliquus externus abdominis. *P < 0.01 and ^# P < 0.05 for pairwise comparisons.