Emg Activation Of Abdominal Muscles In The Crunch Exercise Performed With Different External Loads

Introduction
Compared with the sit-up, the risk for the lumbar spine compression in the crunch is reduced [1,2], but the abdominal
muscles are less activated. So, it is important to find the most effective ways to maximize abdominal activation when
using the crunch for abdominal strength training. The purpose of the present study was to compare the activation level
of abdominal muscles in the first repetition of each set of crunches performed with different external loads.

Methods
13 subjects (5 females, 8 males), performed crunch exercises (knees flexed 90º, legs fixed) with no external load and
with loads representing 100, 80, 60, 40 and 20% of the 1RM, with 5` rest between sets. Surface bipolar EMG electrodes
were placed on muscles of both sides, except for the RF: the upper portion (RAUR and RAUL) and the lower portion of
the Rectus Abdominis (RALR and RALL), the External Oblique (OER and OEL) and the Rectus Femoris (RFR). The
root mean square (RMS) of the EMG was calculated for the first repetition of each load. Mean values and SD of
normalized RMS were calculated. Differences between conditions were tested using the one way ANOVA for repeated
measures. Post-hoc Bonferroni test was used to detect significant differences between specific loads (p < 0.05).

Results
Each subject performed the maximum number of repetitions in each percentage of the maximal external load: 20%
(30±2.8), 40% (26±3.8), 60% (22±5), 80% (14±2.5). When the crunch was performed without external load (0%) the
subjects only performed six repetitions. We used an average of the percentage values of all studied abdominal muscles
as a representative value of abdominal synergy (Ab Syn).

Discussion / Conclusions
Considering the Abdominal Synergy [3] as a representative measure of the abdominal muscles in general we can
conclude that the abdominal muscles were significantly more recruited in the 100% repetition than in the first repetition
of any other external load condition. As we can observe in the Table 2, with the exception of the 100% condition, no
significant differences were found in the Abdominal Synergy between each percentage load and the percentage of the
external load immediately superior and inferior.

References
[1]. Axler, C. & McGill, S. (1997). Med. Sc. Sp. Ex., 29, 804-810.
[2]. Juker, D. et al. (1998). Med. Sc. Sp. Ex., 30, 301-310.
[3]. Andersson, E., et al. (1997). Eur. J. Ap. Phys., 75, 115-123.

NOTA: O texto com a iconografia está no anexo

Arquivo