Involved 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

Squats
 Normal 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 grip
 Wide Grip
 Machine 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
Hamstrings
Glutes
Erector muscles of the back
Gastrocnemius
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 electromyography





Vastus lateralis
Vastus medialis
Biceps femoris
Medial gastrocnemius
Squat Study (cont.)

Methods
 Nine college students
 1 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.