MUSCLE ACTIVATION, MUSCLE SWELLING, AND EXERCISE VOLUME DURING THREE SETS TO FAILURE AT 80% VS. 30% 1RM RESISTANCE EXERCISE
N. JENKINS Journal of Strength and Conditioning Research 2016 VOLUME 30 | SUPPLEMENT 1 | FEBRUARY | S47
However, it is unclear how muscle activation influences these adaptations.
Purpose: Therefore, the purpose of this study was to investigate electromyographic amplitude
(EMG AMP), EMG mean power frequency (MPF), muscle
cross sectional area (mCSA), exercise volume (VOL), total
work and muscle activation (iEMG), and time under concentric
tension (TUCT) during 3 sets to failure at 80% vs. 30% 1RM
leg extension resistance exercise in men and women.
Methods: Eleven men (mean 6 SD; age = 21.5 6 2.7 years; resistance
training per week = 6.6 6 3.7 hours) and 11 women
(age = 22.3 6 3.6 years; resistance training per week = 3.7 6
3.3 hours) completed 1RM testing, followed by 2 experimental
sessions during which they completed 3 sets to failure of leg
extension resistance exercise at 80 or 30% 1RM. EMG signals
were recorded from the 3 superficial quadriceps femoris
muscles of the dominant thigh. An electrogoniometer was
placed across the knee joint to measure joint angle (8). Exercises
were performed on a plate-loaded leg extension device
that was custom fitted with a load cell. Force, EMG AMP
(mV$s21), and EMG MPF (Hz) values were calculated from
signal epochs corresponding to the 608 range of motion occurring
between 1008 and 1608 of leg extension during the concentric
portion of each repetition (rep) based on the
electrogoniometer signal. The EMG AMP and MPF values from
the initial, middle, and last rep of each set were normalized to
a maximal voluntary isometric contraction (MVIC) and used for
analyses. Panoramic ultrasound imaging was used to assess
mCSA of the rectus femoris and vastus lateralis immediately
pre- and post-exercise. Exercise volume, total work, iEMG, and
TUCT were also quantified.
Results: The mean 6 SD for the
numbers of reps completed during sets 1, 2, and 3 were 8.9 6
2.7, 6.7 6 1.9, and 6.2 6 1.7 at 80% 1RM, and 45.6 6 14.3,
26.8 6 8.3, and 22.2 6 8.6 at 30% 1RM, respectively. EMG
AMP increased across reps and sets at 80 and 30% 1RM, but
was consistently greater for 80 than 30% 1RM. EMG MPF
decreased across reps at 80 and 30% 1RM, but decreased
to a greater extent and was lower for the last reps at 30 than
80% 1RM (71.6% vs. 78.1% MVIC). mCSA increased more
from pre-to post-exercise for 30% (20.2 cm2–24.1 cm2) than
80% 1RM (20.3 cm2–22.8 cm2). VOL, total work, iEMG and
TUCT were greater for 30 than 80% 1RM.
Conclusions: EMG AMP remained greater at 80 than 30% 1RM across all
repetitions and during all sets, despite 74 and 147% increases
in EMG AMP during the sets at 80 and 30% 1RM, respectively.
VOL, total work, iEMG, and TUCT were 18–202%
greater, and the decreases in EMG MPF were more pronounced
at 30% 1RM. Furthermore, the increases in mCSA
(i.e., muscle swelling) from pre-to post-exercise were greater at
30 than 80% 1RM.
Practical Applications: Muscle activation was greater during resistance exercise at 80 than 30% 1RM.
Therefore, muscle activation may not be responsible for the
similar hypertrophy observed after 30 vs. 80% 1RM training
to failure. Exercise volume, metabolic byproduct accumulation,
and muscle swelling, however, may be contributing factors.
Additional studies are needed to investigate the acute and
chronic neuromuscular responses to high-versus low-load
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