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Muscle Forces

Involved in bench press and squats. Muscle Forces. 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

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Muscle Forces

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  1. Involved in bench press and squats Muscle Forces

  2. 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

  3. Muscle Activity differences • Bench Press • Free weight vs. Machine Press • Squats • Normal squat vs. Unbalanced squat

  4. 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

  5. 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.

  6. 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.

  7. Results

  8. Results (cont.)

  9. 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.

  10. 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

  11. 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

  12. 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

  13. 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

  14. Results

  15. 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.

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