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Muscle activation patterns while lifting stable and unstable loads on stable and unstable surfaces
James M Kohler1, Sean P Flanagan, William C Whiting
1Department of Kinesiology, California State University, Northridge, Northridge, California, USA.
Journal of Strength and Conditioning Research
|January 15, 2010
Summary
Training on unstable surfaces or with unstable loads, like dumbbells on a Swiss ball, did not effectively increase core muscle activation during shoulder presses. Greater instability led to decreased external load, with no significant benefits for core engagement.
Area of Science:
- Biomechanics
- Exercise Physiology
- Sports Science
Background:
- Exercise programs often integrate trunk and extremity training to mimic 3D activities.
- Unstable surfaces are commonly believed to enhance core muscle recruitment.
- Real-world activities typically involve stable surfaces with unstable loads, not vice-versa.
Purpose of the Study:
- To evaluate muscle activity in prime movers and core stabilizers during seated overhead shoulder presses.
- To compare muscle activation under varying load (barbell vs. dumbbell) and surface (bench vs. Swiss ball) conditions.
- To investigate the effects of combined stable/unstable loads and surfaces on muscle recruitment.
Main Methods:
- Thirty resistance-trained individuals performed seated overhead shoulder presses at 10 repetition maximum intensity.
- Exercises were conducted using a barbell or dumbbell on either a stable bench or an unstable Swiss ball.
- Surface electromyography (EMG) recorded activity in 8 key muscles, including prime movers and core stabilizers.
Main Results:
- Increased exercise condition instability correlated with a decreased external load.
- Triceps brachii activation was highest with a barbell on a bench and lowest with a dumbbell on a Swiss ball.
- Upper erector spinae showed greater activation with barbell presses on a Swiss ball compared to a bench.
Conclusions:
- The study found limited evidence supporting the use of lighter, unstable loads or unstable surfaces for enhanced core muscle training.
- Instability in exercise conditions may lead to reduced overall resistance, potentially limiting training stimulus.
- Conventional training methods with stable loads and surfaces may be more effective for targeting specific muscle groups.
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