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MUSCLE FORCESInvolved in bench press and squats
Muscle Forces
The force generated by a muscle action Depends on:
number and type of motor units activated the size of the muscle the initial length of the muscle when
activated the angle of the joint and the muscle's speed of action
Muscle Activity differences Bench Press
Free weight vs. Machine Press
SquatsNormal squat vs. Unbalanced squat
Bench Press
Most commonly performed exercise, however commonly performed incorrectly.
Major Muscles Used-Pectoralis Major, Anterior Deltoid, Medial
Deltoid, Triceps, Biceps (somewhat). Variations
Close gripWide GripMachine Press
Bench Press Study
Comparison of muscle activity between free weight and machine bench press.
Calculated IEMG values during the ascent and descent phases.
Electromyography reveals periods of electrical activity in a muscle. EMG signal can be used to calculate the
IEMG pattern.
Bench Press study (cont.) Methods
5 male strength trainers- with previous experience on both free weight and machine bench press.
Data collected in two phases○ Phase 1- 1RM was determined for each subject○ Phase 2- Data was collected during bench press performance of
80% and 60% of the 1RM Surface electromyography monitored activity in pectoralis major,
anterior deltoid, medial deltoid, triceps, and biceps. Subjects performed 20 trials, 10 free weight, 10 machine
(Universal machine press). 5 trials at 80% and 5 trials at 60%. 2 min rest between sets.○ Used tape recorded command of 3.0 sec during descent, and 2.9
sec during ascent phases. ○ 5 lift mean for each subject was calculated then used to find group 5
lift mean.
Results
Results (cont.)
Results (cont.) Results support the hypothesis that greater
muscle activity is present during free weights vs. machine.
Difference most evident in the 60% 1RM. Greatest for the deltoid muscles.IEMG was for anterior and medial deltoids was 50
and 33% higher during free weight. There are individual differences in muscle
activity patterns between the two modes.Possibly having to do with joint and muscle
mechanics.
Squats
Considered one of the best exercises for increasing size and strength of legs.
Used in training programs for many sports, often performed incorrectly.
Muscles used:Quadriceps HamstringsGlutesErector muscles of the backGastrocnemius
Squat Study
Isometric squat force output and muscle activity in stable and unstable conditions.
Subjects stood either on force plate, or inflatable balls on top of the force plate.
Recorded electromyographyVastus lateralisVastus medialisBiceps femorisMedial gastrocnemius
Squat Study (cont.)
MethodsNine college students1 testing session
○ 5 min warm-up○ 4 trials for each condition (25 min rest
between conditions)○ 3 min rest between sets
Squat Study (cont.)Isometric squat
○ Force platform (BP6001200, AMTI, Watertown, MA)
○ Fixed bar position at a 100 deg knee angle
○ Maximal isometric contraction for 3 sec.
○ Stable performed standing on plate
○ Unstable performed standing on inflatable balance disks (90 cm)
○ Surface electrodes placed on muscles
Results
Results (cont.) Peak force and RFD were significantly higher in stable
vs. unstable Average IEMG values for VL and VM were significantly
higher in stable vs. unstable No significant differences were found in muscle activity
for the BF or G. Force output of unstable condition was 54.4% of
stable condition. If stable condition is taken at 100% of maximal strength, the
unstable condition would not meet the intensity requirement of 80% for strength gains
No discernable benefit from performing exercises in unstable vs. stable conditions.