1. Biomechanics of a Shoulder Press
Zachery Chen

2. What is a shoulder press?
A weight training exercise performed while standing, in which a weight is pressed straight upwards from the shoulders until the arms are locked out overhead Also called the overheard press or the military press

3. What muscles are used?
The shoulder press mainly targets the shoulders and arms
Primary muscles targeted: anterior deltoid, middle deltoid
Secondary muscles targeted: posterior deltoid, triceps, trapezius, pectoralis minor

4. Push press
An alternate form of the shoulder press is called the push press
Push press movements include an extra push from the legs
Creates for more explosive movement
Many weightlifting experts and coaches say that this detracts from the workout your arms receive.

5. Mechanics of a push press vs. a shoulder press
One continuous movement
Abduction of the deltoid supraspinatus
Upward rotation and adduction of the serratus anterior, pec minor, and trapezius
Extension of the triceps anconeus 1.
Push Press
Broken down into two movements
Dip of the legs creates momentum
Once the legs are extended, the arms follow through 1. 2.

6. Movements in each… Shoulder Press Push Press Hips stay constant
Shoulder and arms rotate up
Weight goes straight up, with little change in x direction
Initial dip in all three points
Similar rotation of shoulder and arms
Weight also goes straight up

7. Questions
How much does the extra boost from the legs detract from the arm workout?
How much more explosive is a push press than a regular shoulder press?
Is there a difference with heavier weights?

8. Shoulder press
Assume that all forces in the X direction cancel out so that ΣFx = 0.
Hips stay at constant Y, so all of the force is generated by upper body muscles and work is done on the 52.16kg weight.
Constant

9. Shoulder press cont. Δh = 0.807m Δt = 1.012s Y of weight:
vy-weight = m/s
Velocity of weight:
ay-weight = m/s2
Y of hips:
vy-hips ≈ 0
Δh = 0.807m
Δt = 1.012s

10. Shoulder press cont. Work = 412.93 J Farms = 513.18 N
Work = ΔKE + ΔPE
ΔKE = 0
Work = ΔPE = mg(hf – hi)
Work = 52.16kg(9.81m/s2)(0.807m) = J
ΣFavg = maavg = 52.16kg(.02861m/s2) = 1.492N ΣF = Fgravity + Farms = 1.492N Farms = 1.492N – Fgravity = 1.492N – mg Farms = 1.492N – 52.16kg(-9.81m/s2) Farms = N
J = mΔv = 52.16kg(.8217m/s) = 42.86Ns
(This is only the initial impulse)
Farms
Fgravity
Work = J
Farms = N
Impulse = 42.9 Ns
Most of the force generated by the muscles in the arms and shoulders go towards counteracting gravity resulting in a low acceleration.

11. Push press Movement broken down into two parts:
Thrust from the legs and arms
Stationary hips, thrust from arms alone
The initial dip brings the entire body and weight down by a constant height
Dip

12. Push press - work Phase 1: Phase 2: Δt1 = 0.269s Δh1 =0.269m
Y of weight:
vweight = m/s
Y of hips:
vhips = m/s
Velocity of weight:
aweight = m/s2
Velocity of hips:
ahips = m/s2
Phase 1: legs + arms
Phase 2: arms only
Phase 2:
Y of weight:
vweight = 1.087m/s
Velocity of weight:
aweight = m/s2

13. Push press – phase 1 Work = ΔKE + ΔPE
Work = 0.5(m)(vf2 – vi2) + mg(hf-hi) Work = 0.5(52.16kg)(1.989m/s) kg(9.81m/s2)(.269m) = J
*1.989m/s from Logger Pro
ΣFavg = maavg = 52.2kg(6.44m/s2) = N
ΣFavg = Fgravity + Farms + Flegs
Assume that the force of the legs on the weight is proportional to the acceleration of the hips.
ΣFavg = mg + Farms + ma = 335.7N = kg(-9.81m/s2) + Farms kg(5.708m/s2)
Farms = N
J = mΔv = 52.16kg(1.989m/s) = Ns
Fgravity
Flegs
Farms
Work = J
Farms = N
Impulse = Ns
The higher impulse depicts a more explosive movement. Additionally, most of the force generated by the legs went into increased acceleration, while force generated by arms stayed relatively constant.

14. Push press – phase 2 Work = ΔKE + ΔPE
Work = 0.5(m)(vf2 – vi2) + mg(hf-hi) Work = 0.5(52.16kg)( m/s) kg(9.81m/s2)(.788m) = J
ΣFavg = maavg = 52.2kg(-3.165m/s2) = N
ΣFavg = Fgravity + Farms
ΣFavg = mg + Farms = N kg(-9.81m/s2) + Farms = N
Farms = N
J = mΔv = 52.16kg(-1.989m/s) = Ns
Farms
Fgravity
Phase 2 of the movement depicts a negative acceleration. Thus the force generated by the arms no longer counteracts gravity with additional acceleration, but rides the momentum generated from phase 1.
Work = J
Farms = N
Impulse = Ns

15. Comparison - work
Work = J
Farms = N
Impulse = -104 Ns
Δt2 = 0.393s Δh2 =0.788m
Work = J
Farms = N
Impulse = 104 Ns
Δt1 = 0.269s Δh1 =0.269m
Work = J
Farms = N
Impulse = Ns
Δh = 0.807m
Δt = 1.012s
Shoulder Press
Push Press
Phase 1
Phase 2
Warms = F1Δy + F2Δy
Warms = N(.269m) N(.788m)
Warms = J
Warms = FΔy
Warms = N(.807m)
Warms = J
Work done by the arms are actually pretty much the same ≈ 420J
Possible reasons:
Push press produces a more explosive force, greater acceleration
Weight is brought to a greater height with push press (1.057m > 0.807m)

16. Comparison - work Shoulder Press Push Press Phase 1 Phase 2
Warms = F1Δy + F2Δy
Warms = N(.269m) N(.788m)
Warms = J
420.88J/540.86J = .778
Warms = FΔy
Warms = N(.807m)
Warms = J
414.13J/412.93J ≈ 1
Work = J
Farms = N
Impulse = Ns
Δh = 0.807m
Δt = 1.012s
Work = J
Farms = N
Impulse = 104 Ns
Δt1 = 0.269s Δh1 =0.269m
Work = J
Farms = N
Impulse = -104 Ns
Δt2 = 0.393s Δh2 =0.788m
When comparing work done by the arms to the total work done on the weight:
In shoulder press, work done by arms comprises all of the work done on the weight
In push press, work done by the arms comprises of only ≈ 77.8% of total work done on the weight – remaining work is done by the legs

17. Comparison - power Shoulder Press Push Press Phase 1 Phase 2
Warms = F1Δy + F2Δy
Warms = N(.269m) N(.788m)
Warms = J
Power = W/Δt = 635.8W
Warms = FΔy
Warms = N(.807m)
Warms = J
Power = W/Δt = 409.3W
Work = J
Farms = N
Impulse = Ns
Δh = 0.807m
Δt = 1.012s
Work = J
Farms = N
Impulse = 104 Ns
Δt1 = 0.269s Δh1 =0.269m
Work = J
Farms = N
Impulse = -104 Ns
Δt2 = 0.393s Δh2 =0.788m
Average power produced by the arms in push press is much larger than in shoulder press
Push press produces a much more explosive movement with ≈ 225W more

18. Questions
How much does the extra boost from the legs detract from the arm workout?
Work done by the arms is similar in both shoulder and push presses
Legs add a considerable amount of work in push press
How much more explosive is a push press than a regular shoulder press?
A push press is significantly more explosive as displayed by the larger power output
Is there a difference with heavier weights?

19. Heavier weights – 61.325kg Phase 1: Phase 2: Δt1 = 0.108s Δh1 =0.050m
Y of weight:
vweight = m/s
Y of hips:
vhips = m/s
Velocity of weight:
aweight = m/s2
Velocity of hips:
ahips = m/s2
Phase 1: legs + arms
Phase 2: arms only
Phase 2:
Y of weight:
vweight = .7065m/s
Velocity of weight:
aweight = m/s2
Shoulder press at kg starts to show hip movement as well
Correlation between heavier weights and hip movement?
Or I just couldn’t lift that much

20. Heavier weights – 61.325kg Phase 1: Phase 2: Δt1 = 0.243s Δh1 =0.436m
Y of weight:
vweight = m/s
Y of hips:
vhips = m/s
Velocity of weight:
aweight = m/s2
Velocity of hips:
ahips = m/s2
Phase 1: legs + arms
Phase 2: arms only
Phase 2:
Y of weight:
vweight = 1.196m/s
Velocity of weight:
aweight = m/s2

21. Calculations Shoulder press: 135lb / 61.325kg
Work = J
Farms = N
Impulse = -115 Ns
Δt2 = 0.985s Δh2 =0.738m
Work = J
Farms = N
Impulse = 115 Ns
Δt1 = 0.108s Δh1 =0.050m
Shoulder press: 135lb / kg
Work = J
Farms = N
Impulse = -97 Ns
Δt2 = 0.387s Δh2 =0.492m
Work = J
Farms = N
Impulse = 118 Ns
Δt1 = 0.243s Δh1 =0.436m
Push Press: 135lb / kg
Workarms = J
Workarms = J
Power = W/Δt = W
Power = W/Δt = W
52.16kg
Workarms = J
Workarms = J
Work done by the arms increase in both shoulder and push press with increased weight
Work done by the arms increased more in the shoulder press
Push press only increased by a little (~4 J), suggesting that most of the additional work is done by the legs
In a push press, additional weight is carried by the legs, but in a shoulder press, most of the additional weight is carried by the arms

22. Calculations Shoulder press: 135lb / 61.325kg
Work = J
Farms = N
Impulse = -115 Ns
Δt2 = 0.985s Δh2 =0.738m
Work = J
Farms = N
Impulse = 115 Ns
Δt1 = 0.108s Δh1 =0.050m
Shoulder press: 135lb / kg
Work = J
Farms = N
Impulse = -97 Ns
Δt2 = 0.387s Δh2 =0.492m
Work = J
Farms = N
Impulse = 118 Ns
Δt1 = 0.243s Δh1 =0.436m
Push Press: 135lb / kg
Workarms = J
Workarms = J
Power = W/Δt = W
Power = W/Δt = W
480.59J/534.26J = 89.95%
424.42J/557.46J = 76.13%
The amount of work contributed by the arms decreases in both instances
In the shoulder press, increased weight causes legs to creep in, contribute force, and do work
In the push press, arms do an incremental amount of additional work to maintain the ratio of work done by arms to legs
Further studies can be done to show this is true**

23. Calculations Shoulder press: 135lb / 61.325kg
Work = J
Farms = N
Impulse = -115 Ns
Δt2 = 0.985s Δh2 =0.738m
Work = J
Farms = N
Impulse = 115 Ns
Δt1 = 0.108s Δh1 =0.050m
Shoulder press: 135lb / kg
Work = J
Farms = N
Impulse = -97 Ns
Δt2 = 0.387s Δh2 =0.492m
Work = J
Farms = N
Impulse = 118 Ns
Δt1 = 0.243s Δh1 =0.436m
Push Press: 135lb / kg
Workarms = J
Workarms = J
Power = W/Δt = W
Power = W/Δt = W
Power = W/Δt = 409.3W
Power = W/Δt = 635.8W
Power also increases in both instances as expected
Both increased by around 35W

24. Questions
How much does the extra boost from the legs detract from the arm workout?
Work done by the arms is similar in both shoulder and push presses
Legs add a considerable amount of work in push press
How much more explosive is a push press than a regular shoulder press?
A push press is significantly more explosive as displayed by the larger power output
Is there a difference with heavier weights?
With heavier weights, hip movement becomes unavoidable
Legs take on more of the work, so difference in work done by arms between shoulder press and push press increases
Increased power, force, and work

25. Further Study Perform experiment with:
larger range of weights
with someone who could lift more.
Analyze force of legs using force plates to see how much force imparted on the ground

26. References http://www.fia.com.au/FIA_mo/fp_archive/fp3.htm
Garhammer, J. O. H. N. "Power production by Olympic weightlifters." Medicine and science in sports and exercise 12.1 (1979):
Garhammer, John. "A review of power output studies of Olympic and powerlifting: Methodology, performance prediction, and evaluation tests." The Journal of Strength & Conditioning Research 7.2 (1993):