Derecruitment of the lumbar musculature with fatiguing trunk extension exercise.
METHODS
This was a descriptive study involving 20 healthy individuals.


OBJECTIVE
To evaluate the neuromuscular activation patterns of the lumbar paraspinal and hip extensor muscles during isotonic trunk extension exercise.


BACKGROUND
Few studies have evaluated the effect of muscle fatigue on the lumbar musculature during isotonic exercise.


METHODS
Electromyographic activity was recorded continuously from the lumbar paraspinal, gluteus maximus, and biceps femoris muscles during isotonic trunk extension exercise performed to muscular failure. Root mean squared electromyography was determined over the concentric portion of each repetition, and polynomial regression analysis was used to describe the association between fatigue and the recruitment patterns.


RESULTS
The lumbar paraspinals demonstrated an increase in the electromyogram signal up to 57.9% of maximal fatigue, at which point decrements in electromyography were observed (lumbar [quadratic curve] R2 = 0.0807, SEE = 0.228; beta2 = -8.245(-5)) (P < 0.000). Associated with fatigue, the gluteus maximus demonstrated an increase in electromyography, with an exponential breakpoint occurring at 35.9% of maximal fatigue (gluteus maximus [quadratic curve]: R2 = 0.5059, SEE = 0.865; beta2 = 0.00017) (P = 0.014). The biceps femoris demonstrated a linear increase in electromyography with fatigue (R2 = 0.4667, SEE = 0.284; beta2 = 0.0091) (P < 0.000). To further investigate the derecruitment of the lumbar extensors associated with fatigue, study participants were analyzed individually with regression analyses. Results revealed that the majority of study participants (68.5%) demonstrated a significant decrease (quadratic bend) in lumbar electromyography, with decrements in muscle activity beginning at 53% of maximum.


CONCLUSIONS
During fatiguing trunk extension exercise, an increase in the lumbar paraspinal electromyogram signal occurs up to approximately 55% of maximum fatigue, at which point a decrease in electromyography is observed. Associated with this derecruitment is a concomitant increase in hip extensor muscle activity, suggesting that as the lumbar musculature becomes fatigued, these muscles allow for continuation of the exercise.
Clark
Brian C
BC
Musculoskeletal Research Laboratory, Department of Exercise Science, Syracuse University, Syracuse, New York 13244, USA. bcclar01@syr.edu
Manini
Todd M
TM
Ploutz-Snyder
Lori L
LL
D000009:Abdominal Muscles / Q000294:innervation / Q000502:physiology; D000328:Adult; D004576:Electromyography; D005260:Female; D006801:Humans; D007551:Isotonic Contraction / Q000502:physiology; D008161:Lumbosacral Region; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*; D011999:Recruitment, Neurophysiological / Q000502:physiology*; D012016:Reference Values; D012044:Regression Analysis; D013909:Thorax / Q000502:physiology