1. Work and Power

2. Work
The product of force and the amount of displacement along the line of action of that force.
Units: ft . lbs (horsepower)
Newton•meter (Joule) e

3. Work = F x d To calculate work done on an object, we need: The Force
The average magnitude of the force
The direction of the force
The Displacement
The magnitude of the change of position
The direction of the change of position

4. Calculate Work
During the ascent phase of a rep of the bench press, the lifter exerts an average vertical force of 1000 N against a barbell while the barbell moves 0.8 m upward
How much work did the lifter do to the barbell?

5. Calculate Work Table of Variables: Force = +1000 N
Displacement = +0.8 m
Force is positive due to pushing upward
Displacement is positive due to moving upward

6. Calculate Work Table of Variables: Force = +1000 N
Displacement = +0.8 m
Select the equation and solve:

7. - & + Work
Positive work is performed when the direction of the force and the direction of motion are the same
ascent phase of the bench press
Throwing a ball
push off (upward) phase of a jump

8. Calculate Work
During the descent phase of a rep of the bench press, the lifter exerts an average vertical force of 1000 N against a barbell while the barbell moves 0.8 m downward

9. Calculate Work Table of Variables Force = +1000 N
Displacement = -0.8 m
Force is positive due to pushing upward
Displacement is negative due to movement downward

10. Calculate Work Table of Variables Force = +1000 N
Displacement = -0.8 m
Select the equation and solve:

11. - & + Work
Positive work
Negative work is performed when the direction of the force and the direction of motion are the opposite
descent phase of the bench press
catching
landing phase of a jump

12. Contemplate
During negative work on the bar, what is the dominant type of activity (contraction) occurring in the muscles?
When positive work is being performed on the bar?

13. EMG during the Bench Press
180 90
On elbow

14. Power
The rate of doing work
Work = Fd
Units: Fd/s = J/s = watt

15. Compare “power” in typical stair stepping
Work = Fd
Force: Push on the step
constant setting
Displacement
Step Height: 5” vs 10”
0.127 m vs m
step rate
56.9 /min vs 28.8 /min
Time per step
60s/step rate
Thesis data from Nikki Gegel
and Michelle Molnar

16. Compare “power” in typical stair stepping
Work = Fd
Force: Push on the step
constant setting
Displacement
Step Height: 5” vs 10”
0.127 m vs m
step rate
56.9 /min vs 28.8 /min

17. Compare “power” in typical stair stepping
Work = Fd
Force: Push on the step
constant setting
Displacement
Step Height: 5” vs 10”
0.127 m vs m
step rate
56.9 /min vs 28.8 /min
Results: VO2 similar fast/short
steps vs slow/deep steps