Week 3: Resistance Exercise Flashcards
Goal of studying resistance exercise
Reduction of Injury
- Balance between stressing the system to adapt and not stressing the system to injury
Maximizing benefits
- Increasing size and strength of muscles and stability of joints, flexibility, power etc
Contraction types
- Isometric
- Isotonic
- Concentric
- Eccentric
- Plymetric
Isometric
Contractions maintain a constant joint angle
Isotonic
Constant force contractions
Concentric
- Active shortening of a muscle
- Change in joint angle in the direction of pull of the prime movers
- Associated with the muscle performing positive work and generating positive power
- Many people associate concentric contractions with accelerating the limb segment, but the velocity can be constant or even decreasing
Eccentric
- Active lengthening of a muscle
- Refers to a change in joint angle away from the direction of pull of the prime movers
- Associated with the muscle performing negative work and generating negative power
- Many people also associate eccentric contractions with decelerating the limb segment, but the velocity can be constant or even increasing
- Eccentric contractions generate greater forces than other contraction types at the same angular velocity
- Require less motor unit activation, consume less oxygen and energy and have a metabolic cost approximately fourfold lower than CON contractions
Plyometric
- Uses the stretch shortening cycle
- The load is allowed to increase dramatically in velocity before an active muscle decrease the velocity to zero with a lengthening contraction
- Muscle remains active in a max effort to dramatically increase the velocity of the load in the opposite direction with a shortening contraction
- Plyometric training may increase lower-limb muscle mass, rate of force development and shorten jumping time
Resistance types
- Infinite
- Body weight
- Free weight
- Progressive resistance according to the strength curve
Infinite resistance
- Isometric exercise that can increase strength and endurance
- Examples are pushing against a wall or immovable object
Body weight and pros
Move own body against the force of gravity
PROS
- Generally Safe due to lack of external load
- Functional training
- Development of stability
Free Weights
- Lifting weight does not provide a constant load to the prime movers but constant mass of weight being lifted
- Different lifters can accelerate the load differently, the resistance is a combination of the gravitational load and the inertial load
- If the lifter moves the weight very slowly, the accelerations are low and the resistance is almost entirely gravitational
- If the lifter accelerates the load rapidly, the initial resistance is considerably larger and then is reduced to less than the gravitational force as it decelerates near the top of the lift
Progressive resistance and the strength curve
- Muscles can generate more force at its optimum length and the moment arm or leverage changes with joint angle
- The strength curve is the moment of force that muscles generate at the joint and are combination of the force-length relation and moment arms of each synergistic muscle group
- Exercises should match strength curves to optimize stimulus on muscles across all ranges
Exercises that are modified to match the strength curve
- Elastics
- Leverage
- CAMS
- Isokinetic Machines
Elasticity to follow the strength curve
- Similar Pectoral Activation: Floor push-up with Thera-Band produces similar pectoralis major activation as a 70% 1RM bench press
- Increased Deltoid activation: Thera band push-up results in 28% more anterior deltoid activation than the bench press
- Enhanced core engagement: Thera-band push-up activates core muscles 4.5 to 5.9 more than the bench press
Leverage to follow strength curve
2nd class leverage is used to lift the weight and as the bar is moved upward, the point of weight application moves closer to the hands which increases the amount of force required to lift the weight
- uses lever to change the amount of force required to lift the weight with the strength curve
CAMS for following the strength curve
- Oval shape of the CAM changes the moment arm as it rotates during the movement
- Designed to follow a generic strength curve increasing resistance where muscles are strongest
- Different CAM required for each exercise
Isokinetic Machines
Adjust resistance to match each lifter’s changing strength, fatigue, and lifting speed
Hydraulic Cylinders
Replace traditional weight stacks, using a piston moved through a cylinder filled with hydraulic fluid to provide resistance
Pneumatic cylinder
- Similar to hydraulic but are filled with air
- Less expensive but air is more compressible so the velocity is not exactly constant
Electromechanical Motors
Isokinetic dynamometers driven by electromechanical motors are commonly used in therapeutic clinics for controlled resistance training
Free weights vs Machines
- Safety concerns of dropping free weights on yourself
- Isolation: Machines target specific muscle groups and reduce technique issues, but neglect stabilizing muscles
- Specificity: Free weights allow for multi-segment movements that also engage stabilizing muscles
- Eccentric loading: Free weights provide eccentric loads equal to CON loads offering better overload for muscle growth
Force in slow vs fast lifting
Lifting weight slowly involves moderate force changes, while lifting quickly generates significantly greater forces due to rapid acceleration
- the resistance in lifting is directly influenced by the acceleration of the load
Heavy vs fast lifting debate
- Many argue lifting heavy weights slowly with fewer reps builds both strength and speed, avoiding injury
- Newton’s second law argument: Stronger muscles produce greater force, increasing acceleration and speed without lifting faster
- Strength and speed are not directly related; strongest athletes are not necessarily the fastest
Role of Fatigue
- Muscle growth is stimulated by lifting to the point of fatigue, making additional repetitions impossible
- Slowly lowering the last repetition maximizes eccentric strength and exercise fatigue
