Spinal flexibility affects range of trunk flexion during performance of a maximum voluntary trunk curl-up

The present study investigated the relationship between spinal flexibility and range of trunk flexion during curl-up performance. Fifty young adult men (age: 18.93 +/- 1.31 years; height: 179.4 +/- 5.7 cm; mass: 73.95 +/- 7.8 kg) performed a spinal flexibility measurement test and a maximum voluntary trunk curl-up from the supine position. The 2 tests were paced to the beat of a metronome and had a constant movement duration set to 5 seconds. Spinal and pelvic motions were recorded with the help of 2 electromagnetic tracking sensors (Flock of Birds, Ascension Technologies, Inc., Burlington, Vt; sampling rate 100 Hz) attached to the seventh cervical (C7) and first sacral (S1) vertebrae, respectively. Correlation and linear regression analyses revealed a significant relationship between spinal flexibility and curl-up performance, with spinal flexibility accounting for 18% of the variance in the range of trunk flexion during performance of the voluntary trunk curl-up. No significant anterior tilt of the pelvis was noted during performance of the trunk curl-up. On the other hand, a minor posterior pelvic rotation depicted during the initial phase of the trunk curl-up was negatively correlated with spinal flexibility. It is concluded that a normal range of spinal flexibility is critical for the optimal performance of abdominal strength training exercises such as trunk curl-ups from the supine position. The results of the present study are relevant to the design and evaluation of training programs for improving strength and function of the abdominal muscles in rehabilitation and sports contexts.