Biomechanics of a Shoulder Press Zachery Chen

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

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

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.

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.

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

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?

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

Shoulder press cont. Δh = 0.807m Δt = 1.012s Y of weight: vy-weight = 0.8217 m/s Velocity of weight: ay-weight = 0.02861 m/s2 Y of hips: vy-hips ≈ 0 Δh = 0.807m Δt = 1.012s

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) = 412.93J 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 = 513.18N J = mΔv = 52.16kg(.8217m/s) = 42.86Ns (This is only the initial impulse) Farms Fgravity Work = 412.93 J Farms = 513.18 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.

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

Push press - work Phase 1: Phase 2: Δt1 = 0.269s Δh1 =0.269m Y of weight: vweight = 1.621 m/s Y of hips: vhips = .8922 m/s Velocity of weight: aweight = 6.436 m/s2 Velocity of hips: ahips = 5.708 m/s2 Phase 1: legs + arms Phase 2: arms only Phase 2: Y of weight: vweight = 1.087m/s Velocity of weight: aweight = -3.165m/s2

Push press – phase 1 Work = ΔKE + ΔPE Work = 0.5(m)(vf2 – vi2) + mg(hf-hi) Work = 0.5(52.16kg)(1.989m/s)2 + 52.16kg(9.81m/s2)(.269m) = 240.82J *1.989m/s from Logger Pro ΣFavg = maavg = 52.2kg(6.44m/s2) = 335.7 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 = 52.16kg(-9.81m/s2) + Farms+ 52.16kg(5.708m/s2) Farms = 549.66N J = mΔv = 52.16kg(1.989m/s) = 103.75Ns Fgravity Flegs Farms Work = 240.82 J Farms = 549.66 N Impulse = 103.8 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.

Push press – phase 2 Work = ΔKE + ΔPE Work = 0.5(m)(vf2 – vi2) + mg(hf-hi) Work = 0.5(52.16kg)(0 - 1.989m/s)2 + 52.16kg(9.81m/s2)(.788m) = 300.036J ΣFavg = maavg = 52.2kg(-3.165m/s2) = -165.21 N ΣFavg = Fgravity + Farms ΣFavg = mg + Farms = -165.21 N 52.16kg(-9.81m/s2) + Farms = -165.21 N Farms = 346.48N J = mΔv = 52.16kg(-1.989m/s) = -103.75Ns 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 = 300.036 J Farms = 346.48 N Impulse = -103.8 Ns

Comparison - work Work = 300.036 J Farms = 346.48 N Impulse = -104 Ns Δt2 = 0.393s Δh2 =0.788m Work = 240.82 J Farms = 549.66 N Impulse = 104 Ns Δt1 = 0.269s Δh1 =0.269m Work = 412.93 J Farms = 513.18 N Impulse = 42.86 Ns Δh = 0.807m Δt = 1.012s Shoulder Press Push Press Phase 1 Phase 2 Warms = F1Δy + F2Δy Warms = 549.66N(.269m) + 346.48N(.788m) Warms = 420.88J Warms = FΔy Warms = 513.18N(.807m) Warms = 414.13J 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)

Comparison - work Shoulder Press Push Press Phase 1 Phase 2 Warms = F1Δy + F2Δy Warms = 549.66N(.269m) + 346.48N(.788m) Warms = 420.88J 420.88J/540.86J = .778 Warms = FΔy Warms = 513.18N(.807m) Warms = 414.13J 414.13J/412.93J ≈ 1 Work = 412.93 J Farms = 513.18 N Impulse = 42.86 Ns Δh = 0.807m Δt = 1.012s Work = 240.82 J Farms = 549.66 N Impulse = 104 Ns Δt1 = 0.269s Δh1 =0.269m Work = 300.036 J Farms = 346.48 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

Comparison - power Shoulder Press Push Press Phase 1 Phase 2 Warms = F1Δy + F2Δy Warms = 549.66N(.269m) + 346.48N(.788m) Warms = 420.88J Power = W/Δt = 635.8W Warms = FΔy Warms = 513.18N(.807m) Warms = 414.13J Power = W/Δt = 409.3W Work = 412.93 J Farms = 513.18 N Impulse = 42.86 Ns Δh = 0.807m Δt = 1.012s Work = 240.82 J Farms = 549.66 N Impulse = 104 Ns Δt1 = 0.269s Δh1 =0.269m Work = 300.036 J Farms = 346.48 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

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?

Heavier weights – 61.325kg Phase 1: Phase 2: Δt1 = 0.108s Δh1 =0.050m Y of weight: vweight = 0.5299 m/s Y of hips: vhips = .2991 m/s Velocity of weight: aweight = 5.570 m/s2 Velocity of hips: ahips = 0.4491 m/s2 Phase 1: legs + arms Phase 2: arms only Phase 2: Y of weight: vweight = .7065m/s Velocity of weight: aweight = -.1871m/s2 Shoulder press at 61.325kg starts to show hip movement as well Correlation between heavier weights and hip movement? Or I just couldn’t lift that much

Heavier weights – 61.325kg Phase 1: Phase 2: Δt1 = 0.243s Δh1 =0.436m Y of weight: vweight = 1.872 m/s Y of hips: vhips = 1.059 m/s Velocity of weight: aweight = 7.942 m/s2 Velocity of hips: ahips = 8.268 m/s2 Phase 1: legs + arms Phase 2: arms only Phase 2: Y of weight: vweight = 1.196m/s Velocity of weight: aweight = -4.127m/s2

Calculations Shoulder press: 135lb / 61.325kg Work = 473.55 J Farms = 589.26 N Impulse = -115 Ns Δt2 = 0.985s Δh2 =0.738m Work = 60.71 J Farms = 914.29 N Impulse = 115 Ns Δt1 = 0.108s Δh1 =0.050m Shoulder press: 135lb / 61.325kg Work = 150.845 J Farms = 348.0 N Impulse = -97 Ns Δt2 = 0.387s Δh2 =0.492m Work = 406.619 J Farms = 580.75 N Impulse = 118 Ns Δt1 = 0.243s Δh1 =0.436m Push Press: 135lb / 61.325kg Workarms = 480.59J Workarms = 424.42J Power = W/Δt = 439.70W Power = W/Δt = 673.68W 52.16kg Workarms = 414.13J Workarms = 420.88J 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

Calculations Shoulder press: 135lb / 61.325kg Work = 473.55 J Farms = 589.26 N Impulse = -115 Ns Δt2 = 0.985s Δh2 =0.738m Work = 60.71 J Farms = 914.29 N Impulse = 115 Ns Δt1 = 0.108s Δh1 =0.050m Shoulder press: 135lb / 61.325kg Work = 150.845 J Farms = 348.0 N Impulse = -97 Ns Δt2 = 0.387s Δh2 =0.492m Work = 406.619 J Farms = 580.75 N Impulse = 118 Ns Δt1 = 0.243s Δh1 =0.436m Push Press: 135lb / 61.325kg Workarms = 480.59J Workarms = 424.42J Power = W/Δt = 439.70W Power = W/Δt = 673.68W 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**

Calculations Shoulder press: 135lb / 61.325kg Work = 473.55 J Farms = 589.26 N Impulse = -115 Ns Δt2 = 0.985s Δh2 =0.738m Work = 60.71 J Farms = 914.29 N Impulse = 115 Ns Δt1 = 0.108s Δh1 =0.050m Shoulder press: 135lb / 61.325kg Work = 150.845 J Farms = 348.0 N Impulse = -97 Ns Δt2 = 0.387s Δh2 =0.492m Work = 406.619 J Farms = 580.75 N Impulse = 118 Ns Δt1 = 0.243s Δh1 =0.436m Push Press: 135lb / 61.325kg Workarms = 480.59J Workarms = 424.42J Power = W/Δt = 439.70W Power = W/Δt = 673.68W Power = W/Δt = 409.3W Power = W/Δt = 635.8W Power also increases in both instances as expected Both increased by around 35W

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

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

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): 54-60. 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): 76-89.