Topic: btay - tastes like parkour (HIpk)

[Gregg]

My R ankle is still healing. Today I can bear full body weight on it, and go up on my toes. Side to side, still quite a bit of pain. I tried a couple vaults yesterday at GWR. It felt pretty good. It was stupid thing to do.

Links for beginners:
Getting Started, APK warmup, Construct workout, APK Landing, APK Roll, Team Ukemi Roll, Eliminate roll bruises, Jump Westminster because it shows Forrest and Dan training beginners.

Here are a couple games I invented...

Jump on the Pennies:
Go barefoot. Put two pennies down, a foot or two apart, 2 - 3 feet away from you. As you jump, focus on the pennies, and try to land on them with the balls of your feet. Toss the pennies 2-3 feet away, and do it again. When you think you have this down, try NOT landing on the pennies. Land with the balls of your feet like 3 inches to the outside of each penny. What you're doing is deciding where the safe [or unsafe] place to land is, and then trying to hit the safe spot. You're also trying to build up the strength in your legs.

Alpha-butt Hula:
Put your legs a little more than shoulder width apart. Bend at the ankles, knees and hips as if you're dancing hula. Now, pretend your butt is a pencil. Write the alphabet. Do it horizontally, like hula, then vertically. Definitely start off small and slow. Then as you warm up, you can make the letters bigger. There are 3 axis... x=side/side, y=up/down, z=front/back. So you can write on x/y, x/z, and y/z.

[Gregg]

Last night I was trying to work out the physics of jumping. It's been too long, and my math skills are very rusty. These are my rough guesses of accelleration from gravity: [I know it's 9.8 m/s but 10 was easier to work with]

1m @ .25 sec = 4m/sec = 9 mph
3m @ .50 sec = 6m/sec = 13.5 mph
6m @ .75 sec = 8m/sec = 18 mph
10m @ 1 sec = 10m/sec = 22.5 mph

My current mass is 74 kg [163#]. I should be able to calculate the force needed to jump the various heights. I don't have time right now... or remember the formula. I should also be able to calculate the force of impact from those heights [If I landed bad]...

[Steven Low]

The force is actually VERY hard to calculate because you need to take into account how much the ground "bends" and how much force is absorbed by the joints. That's why Demon had that whole project (that he never updated ) with force plates and landings in the lab. You need pretty advanced calculus and differential equations to model something like this.

I also don't know where you are getting your times either.. that you can calculate with the mechanics equations. Acceleration is 9.8 m/s^2 not a m/s so that throws off all your calcs. It would be something like:

X = X0 + V*t + 1/2 at^2

then use quadratic to solve for time:
1m: .452s
3m: .782s
6m:  1.107s
10m: 1.429s

then X = V*T so V = x/t
1m/ .452s = 2.214 m/s
3m/ .782s =  2.834 m/s
6m/  1.107s = 5.422 m/s
10m/ 1.429s = 7 m/s

That's about all you're gonna get unless you want to go deeper which I don't really want to. But as you can see the higher you jump the more it's gonna hurt because of more acceleration on the body over a greater amount of time.

BTW, 10m is ~33 ft.. I don't think you want to jump that far.

[Steven Low]

Gah, stupid time edit limit. should be 3.834 m/s for the 3m one.

[whiteninja]

BTW, 10m is ~33 ft.. I don't think you want to jump that far.

Always meant to post this, always been too lazy. Selling the book tomorrow though, so I had better do it now.  Hahah.

From my Physics textbook: Physics: Principles with Applications by Prentice Hall Press, pg189
From what maximum height can a 75kg person jump without breaking the lower leg bone of the either leg? Ignore air resistance and assume the CM of the person moves a distance of .60m from the standing to the seated position (that is, in breaking the fall). Assume the breaking strength (force per unit area) of bone is 170 x 10e6 N/m^2, and its smallest cross-sectional area is 2.5 x 10e-4 m^2. [Hint: Do not try this experimentally.]


Look below for the answer, if you don't want to do the calculations. Took me forever to figure out. I kept forgetting that people have two legs!!!

That isn't to say you won't break all your other bones though!






























69 meters.

[Gregg]

"Math is hard" - Barbie Mattel received a lot of hate for having her say that.

The bridge at Kipahulu/ Ohe'o/ 7 Sacred Pools is 55' [into water, or rock if you don't jump right.] To get down from there, is another 45' jump [into water, if you clear the bushes]. Landing feels like getting hit in the butt by a 2x4. I don't want to jump from that height again, but people do it all the time. Someone jumped off Makahiku Falls [200'], but he was on mushrooms, so it doesn't really count. I don't know if he died instantly.

Whiteninja: can you take out the white space, please?

I was using m/s because I thought 10 m/s/s accelleration for 1 second = 10 m. I thought: 10 m in 1 second = 10 m/sec. I saw something yesterday that first second = 5 m in free fall. I don't understand that, and need to look into it.

Yesterday's "workout"
I worked HI 7:30 am to 3 pm, GWR from 3:30 pm to 9:15 pm. Because I knew this, I did little bits of workout throughout the day. I was wearing dress clothes and dress shoes, working in a business/ luxury environment. I tried to write it down on a scrap of paper, but I know I missed stuff.

AB hula = 3 dimensions, + xy [stopped at "s" due to ankle pain] + xy wide stance + xy narrow stance
Cat crawl 10' on 6" log railing. Mild discomfort. 20' on brick wall = fine. 2 hand vaults up and landings = ok.
Squats = 50 + 20.
Vertical jump = 8" ok, 13" ok. 15" hurt.
Broad jump = 6' ok. Didn't feel like pushing my luck.
Hopped on L leg as high as possible while holding onto something = 20 + 20 + 20
Pull ups = 5 + 5 stairwell railing, + 5 + 5 lattice overhang, + 5 stair landing [floor]
Dips = 5 handicap bathroom stall + 5 equipment carts + 5 stair railings
Played Jump on the Pennies about 15 times, using spots on the flagstone.


Exploring:
GWR between Chapel Overlook and Kincha: NOTE: If you do not have permission to be on hotel grounds, this could be considered class 1 criminal trespassing. I have permission to be on grounds, since I'm working there. I could probably still get in trouble.

Chapel Overlook, mauka to Kincha: Wall + rail to small grassy area, lattice overhead. S side drop is small, but toward the middle it's 45' or so to foliage/ dirt/ rock. A few palms within jump distance [maybe] if you're insane. Steep gully with rails and staircases - rails are low 6" dia logs. Pathways are flagstone/concrete, wet in some spots. Few paths in foliage - could be a slippery climb. Pond near Kincha - rock and foliage lined. Rocks in center - many good sized but too far to jump right now. Easy jump from rocks to Kincha - but garden hoses coiled on ground... Path around N side of pond to kids' camp area. Day = sunlight, night = widely spaced gas torches + residual light from other areas of resort.

Goals:
Stretch and strengthen ankles until pain free. Force myself to not jump/ vault/ run too much until healed.
Build back up to jog to Maalaea and back from home, barefoot. [About 10 miles, on pavement, grass, sand, rock and coral.]
Jump/ muscle up out of pool @ 5' to my feet [can do 4'6"]
Work on landings < 6" until ankle = pain free.
1 good handstand pushup on dry ground. [I do them in pool/ ocean until I run out of air]
1 muscle-up from dead hang.

Explore GWR from ballrooms to main lobby today, from PK viewpoint.
Continue writing "Beginner" article - 1/2 hour.
Finish Deut. by end of month.

[Gregg]

HI 7:30 - 2, GWR 2:30 - 7. Worked on "Beginning" article for a couple hours afterwards. No interruptions 

Training: [in dress clothes/ shoes, scattered over 5 hours, not in this order]

AB hula: 2 x 3 planes = xz cursive, the others with block letters. Yesterday's should also read xz, not xy. Also did wrists and arms on cool-down.
Squats: 20 + 20
Pullups: 5 on carport [8" jump hurt], 5 + 5 on stair rail, 5 on overhang, 5 on plumeria tree. Tried to muscle up into tree, but could only get pullup. Sprinkler pipe too weak. Decided not to pull on AC ductwork.
Cats onto 5' laundry cart - felt good. Decided not to on chain link fence.
Dips: 5 on portable stairs, 5 + 5 + 5 on stair railings, 5 on a cart for moving tables.
36" jump/ underbar onto sky-lift. The jump hurt.
Small jumps onto things, jump on the pennies using spots on stair landings, Run through GWR to Shops - jumped on a couple planters along the way, but that was probably not wise.
Pop/ muscle up 6'3" tablecloth rack.
3 x 2 hand vault onto 38" wall, balance/ cat crawl to palm tree. Grab base of fronds, step over, slide down.
2 x 30 sec sit against wall
Handstand with heels on wall 15 seconds. Fell when tried to hspu. Slight wrist discomfort.
2 x 6'6" long jumps.


See? Exercise doesn't have to be boring. Even when you're recovering from injury, have little upper body strength, have to work 12 - 14 hours, and are wearing dress clothes and dress shoes. There's no excuse for letting myself go as far as I did...

Exploring GWR:
Outside ballrooms. I've been eyeing the 8-12' falls. There are several places where it would be easy to jump onto them from the flagstones [if my ankle was healed]. Water and moss are things to watch out for. Also, bougainvillea [thorns], ginger and plumeria [sap] at top of falls.

Around the corner of Hale 4-5, on way to lobby, it's rock wall. There's a nice u shaped section that could be fun for cat to cat or precisions, if you don't mind being 10' up. Long staircases w/ brass rails up to lobby.

Chapel gazebos. 8' interior dia. Nice low bench. Upper circle starts about 8' above that. Not sure if ironwork can support weight at force or not. Lots of seed pods and rocks in the ground cover

Won't post locations any more. It's time consuming, and I've better things to do.

D3:11 `eres barzel = Basalt coffin or iron bedstand? Mittah's the more common word for bed or bier. `eres is usually translated bed, couch or bedstead. 'arown is the word for chest or coffin. Sure they were a bronze culture for a couple hundred more years, but I think they could tell the difference between iron and rock.
:26 Blame the people for your anger, pride and disobedience. Good job, Mosheh.

Writing goal met. Try 1 more hour today.
Explore goal met - new: Check out skate park when ankle is healed.
New goal: audition for 'American Daze' is tonight at 5 pm. Cool. 2 weeks from audition to production. I saw the video from 2005. My dancing in "Semantics" was ridiculous, as usual. I think I couldn't get the steps everyone else was doing, so I twisted, jumped and spun freestyle. My intro and guitar work for "Pull My Plug" - I was happy with it. Simple 5ths and power chords.

[Steven Low]

The mechanics needed to solve for velocity in a certain fall is the same one I used above:

X = X0 + V*t + 1/2 at^2

Take the variable "t" as an x value and you have ax^2 + b*x + c = 0 which can be solved by the quadratic to get the value of x.

[-b +/- sqrt(b^2 - 4*a*c)]/(2a)

Once you find X, that's the amount of time you spent falling from that certain height. To get velocity, you just divide the distance (which you set up already as X-X0) by the time which you just solved for. See my above post for the details. As you can see the 6m falling time is just over a second which puts the 5m falling close to a second at 5 m/s.

[Gregg]

Saturday: L wrist and chest were very sore - I'll blame the failed HSPU - trying to do too much, too fast.

Biked to work
AB hula = 3d + arms.
Balance work on rail.
Pull ups = 5 awning + 5 equipment rack
Long jump 6 1/2 feet.
Bike home.
Random dancing about 15 min w/ some AB hula/ arms mixed in.

Sunday: Got kicked in the bad ankle [accident]. Ow. Chest still sore.
AB hula = 2 x 3d
Pushups = 20 sissy, + 11 feet on chair, + 10 feet on chair.
Walk around barefoot 10-15 minutes. Pavement was HOT.
Pull ups = 5 tree A, + 5 mail center, + 5 tree B, + 5 tree C
Random dancing 17 min.
Barely dancing for a while. It was so pathetic...

Monday: Ankle felt good enough to vault!
2 hand, 1 hand, lazy, and reverse vaults. Started to feel it in my ankle and knees, after about 50 vaults. Did hit my knee on one vault, not hard, tho.
Elliptical: 10 minute hard warmup, 30 minutes close to 150 bpm, 5 minute slow cooldown.
Cybex: 3 x 10 reps, fairly light weights.
Pool: 1/2 hour playing. I could jump/ muscle up out at 4 1/2 feet barely. At 5 1/2 feet, I was too far under water when I crouched - couldn't get the coordination down.
Walked around barefoot 5 minutes. Sprinted about 100 yards. It felt good.
7' standing broad jump.
Pullups: 5 plumeria tree + 5 equipment rack. Arms tired from Cybex. That's my excuse.

Gym stuff was w/ M & G. Much more fun than working out alone. They've both seen "Jump London"... wonder if I can get them to try some basic stuff?

New goal: Jump the fish pond. I did it before I got hurt...

[Gregg]

Someone asked "How do you train new movements?". Since I spent far too much time writing a reply, I thought I'd include my answer here. I don't like reinventing the wheel. I'd rather steal from myself, than have to look for the answer again. This is based on someone else's answer a few months back, but I couldn't remember where that was...

I like to break a new movement into different parts, and get each part comfortable before I try to put it all together. If I feel comfortable - my technique is good, I'm feeling strong, and I'm mentally up, I move on to the next step. If not, I either try the technique again, or I move on to something else. If I feel pain, I back off immediately.

I started with a 2 handed vault. It's not listed in most lists of PK moves. Here's a bad youtube "tutorial", to give you the general idea. I started with a heavy molded plastic table on carpet. A low wall with grass on the landing side would probably be better.

1. Handplant and jump: First I practiced from standing 12 - 18 inches from the wall. I put my hands on top of the wall, right a little forward of the left. Put some weight on them.  I jumped to the top of the wall as softly and quietly as I could. Feet land to the right of my hands. Then I softly and quietly jump back down to starting position. Repeat like  5 to 10 times, to get comfortable.

2. The other side: Reverse, and do the same thing to the left. For me, this wasn't as natural, so I had to practice it a few more times.

3. Jump, then land: Back to the right. This time, instead of jumping back to the start place I'll lift my right hand, keep weight on my left hand and jump straight down in front, trying to land as soft and quiet as I can. I use my left hand to help balance me, control my landing. Try to smooth the whole process.

4. Vault: When you're comfortable with that, try the vault in one movement. Repeat until you're comfortable.

5 & 6. The other side: Try it to the left. Repeat until you're comfortable.

7. Approach: Now walk up to the wall, slowly, and try to vault it. You can already do it from standing. If you find yourself freezing, try walking up to the wall and vaulting on top of it. When you can vault from a walk, try it from a jog. When you're comfortable, try it from a run.

8. The other side.

9. Find something completely different to do. Maybe quad movement, or climbing a tree, or practice rolling. Do something where you're not using the muscles you just used in the way you were using them. Give them a rest.

Nx 1. The next time... Try vaulting to the top from a walk. If it feels good, try vaulting from a walk, then a run. If it doesn't feel good, or your technique isn't good, back up a step.

Nx 2. Variations: Try different approach angles. Try a different wall. Maybe something a couple inches higher. Try rolling after you land.

Nx 3. Something completely different: Give your joints and muscles a rest.

Nx 4. A new vault... Try speed vault if your wall is low. M2 likes kong because it's fast and efficient. Other people suggest the lazy vault. I was more comfortable trying reverse.

That's the basic process I use. I hope that helps you...

[Gregg]

Yesterday was the first time since May 21 that my ankle felt good. It's been almost a month of very minimal PK.

Today: Bike to work. Did about 15 little vaults - 2 hand, 1 hand, concentrating on left side. A few reverses. My landings were louder than I like. Part of it's the dress shoes. Form is not 100%.

Walk/ jogged --> ASB --> FHB --> back. They're tearing up the woods behing work. The tents of the homeless people are gone. There were a few old ruined buildings I wanted to check out, but was always too cautious. The buildings are still there, so I took a look. One was an old shed, large garage size, with probably 5 years of homeless people garbage on the ground. The other was a dilapidated pump house, the pump all rusty and metal lying on the ground. They weren't nearly as magical or threatening as they looked last week. I'm going to miss the woods.

To get back there = 6' drop onto kiawe - long thorns everywhere. Instead, I found a fallen tree I could walk down. Still got stabbed a couple times.

I did a lot of cat leaps and cats to leg-assisted muscle ups on 5' Dumpster containment walls. I was like "That was a ten foot wide jump, and my feet are still three feet above the ground!" I felt strong. Conditioning for the last month has really helped. A bunch of rail vaults, balance work. Short cat crawl. Precision to precision to precision to get around some thorny tiare. Tried to do some 7' wall pops, but it just didn't work, and I had to play "Dodge le Traffique".

Back at work, feeling great, pumped. Shimmied along some chain link fence. Got Rubbermaid trash can out onto the grass, and tried a couple kongs. I wasn't confident. First one was more like a 2 hand jump, with my butt high in the air. Second one, R toe clipped the can. Crash and burn. Argh.

Right ankle said, "Try it again, and you won't jump for another month."
Right wrist said, "I won't support you if you try this again."
Back said, "Do you realize you haven't done any rolls since you pulled your ankle? You need to go back to square one, train like a total noob."

I try to listen to my body. Even when I don't like what it says. So I dragged the trash can back to the loading dock, and went back in to work.

[Muse_of_Fire]

Right ankle said, "Try it again, and you won't jump for another month."
Right wrist said, "I won't support you if you try this again."
Back said, "Do you realize you haven't done any rolls since you pulled your ankle? You need to go back to square one, train like a total noob."

I try to listen to my body. Even when I don't like what it says. So I dragged the trash can back to the loading dock, and went back in to work.

This made me giggle. But listening to your body is always a good idea. Right now, my mind is saying, "I will let you run as long as you like," and my legs and lungs are saying, "F-U." 

It's hard to get back in the saddle, but it looks like you're well on your way. Good luck!

[Gregg]

I thought I was well on my way, too. I'm not. Not yet.

I normally grab 5 pull ups here, 20 squats or AB hula while I'm waiting over there. My "workout" is usually a bunch of one to two minute bursts spread over an eight to fourteen hour work day.

Today I tried to do the full APK warmup for the first time in over a month. Pathetic. First, I didn't remember it - I was doing my burpees and quad movement after the samson stretches, and it just wiped me out. I only got about 1/2 way through the warmup.

I decided to run. Jog barefoot around the soccer field. Jog, jog, jog. How boring. So I decided to sprint from one goalpost to the volleyball net, etc. I tripped, and fell.

Went to the pool. Jumped the fishpond twice. Goal accomplished. My landings were terrible. I haven't done precisions at that speed and distance for over a month. I was lucky I didn't hurt myself. Rock climbing was slow.

So I soaked in the pool for 15 minutes, then walked around barefoot on the pavement for about 7 minutes to dry off.

I'm not happy with today. I'm not even in beginner shape any more. I thought I was, but I'm wrong. Sigh...

[Gregg]

Biked to work. Walked to see how much they had destroyed the woods, and back. Did not fall down. Did not get hurt. Biked home.

There are some things bothering me with the beginner article... it's a whole PK mindset thing... I'm missing some important things, and I can't figure it out... bear with me... it feels wrong, if you know what I mean. It's not necessarily physical and tangible.

There's a balance between extremes: Risk and security.
Does No Risk: No Security exist? Maybe it's just an illusion? I don't know. Sitting in your easy chair, doing nothing. Fat and happy. You can't control many of your own body functions. There's still risk. There is some risk in just living. You can't eliminate all risk. There is no guaranteed security, because there are always things that are beyond your control. If you were dead... everything's beyond your control.

Very Low Risk: Very High Security (survival/security - mental focus = fear/loss) --> Short obstacles, soft obstacles and landing areas, protective gear, no jumps or vaults over [height] for [duration]. Check every obstacle before jumping. Emphasis on conditioning, proper form. High repetition at low intensity. Slow progress, if any. Mental picture = prison of own making = person wrapped up in padding, inside a padded room, surgical mask, no sharp objects, etc.

Very High Risk: Very Low Security (attention/ego/adrenaline/variety - mental focus = accomplishment) --> Tricks off high obstacles. Train without any protection. Low repetition at high intensity. Fast progress followed by injuries. Perhaps crippled for life. [Logical progression] Mental picture = crippled vegetable = a carrot, frowning, hooked up to IV, with all sorts of bandages.

How to get safely to a physical state like David Belle - able to manuever safely in a very high risk environment? Maintain a high level of conditioning into your 90s?

Top 5 causes of death in USA 2001 [per CDC]
Heart disease, cancer, stroke, chronic lower respiratory disease, unintentional injuries...

What you eat, smoke and drink, and the amount of exercise you get are major factors in the first four... They're factors you can do something about.

Top 5 causes of accidental death in America: [soyouwanna.com - not so credible - source for # not given.]
1 Motor vehicle crashes: 43200 deaths per year
2 Falls: 14900 d/y
3 Poisoning by solids & liquids: 8600 d/y
4 Drowning: 4000 d/y
5 Fires and burns: 3700 d/y

[Firearms is #7: 1500 d/y.]

That's not good news for PK people. I don't think most of us realize how many people die from accidental falls. It's 10x the amount of people dying accidentally from firearms. So that's a major thing to take into account. Sigh. Why does this little article have to be so messy?

[Steven Low]

I wouldn't worry. As long as you are taking proper precautions you should be fine (which you already know). Honestly, 3x more people die from a car accident than those accidental falls. I mean, come on.. there's a greater chance of that than falls AND we are taking calculated risks here -- not unnecessary risk.

[Gregg]

I'm not worrying. I'm stalling from writing the Beginner section, because there's something wrong with it. That's my excuse. I was just trying to work it out.

Biked to work. Biked to MWO [about 7 miles]. Worked there a couple hours. Watched Foucan's run in Casino Royale. Biked back to work. Tried to do APK workout. Exhausted. Couldn't even do 1 cycle due to wrist and ankle pain. Biked home.

G&M are supposed to come over to work out with me.

Goals:
Stretch and strengthen ankles, knees and wrists. No jump/ vault/ sprint until APK warm-up without pain.
Finish "Beginner" article - rough by Wednesday, submit to M2 by June 30.
Finish Deut. by end of month.
Landings: up to 18" at jog this week.
Maalaea: Jog 10 min barefoot this week.

Postpone: 1 good handstand pushup on dry ground. 1 muscle-up from dead hang. Skate park.

[Gregg]

Biked to work. Exhausted. Tried APK Warmup. Samson stretches hurt R ankle. Pullups on equipment rack - pathetic. I did not even have strength to do 4. Over an hour of constant interruptions midway through second circuit. This is par for the course. Finished off squats and spus. Couldn't Samson - tried 3 more and just had to give up.

[Gregg]

Sun: M, G & I hiked at Hosmer Grove 7000' and Haleakala 9000' [near summit]. I was in slippers - ok except for balance work and big downhills. I could tell my balance was off due to foot and ankle injuries. At 9k' I think I was feeling lack of oxygen, tho not as bad as G was.

Today: Flat tire. Jogged to work instead. Felt pretty good. I work at MOW later this morning, then straight to KC for rehearsals. That should last until 10pm or so. No time for a big work out today.

[Gregg]

Upped my stairwell pullups 6+6+3+6. Did a little exploring - found a couple great places S@W --> MOW, if you like 15' drops. I don't. 36 squats. A few vaults onto equipment cases.

Started today with 30+10 SPUs and jogged to work.

[Gregg]

I was still struggling with the physics of PK. I asked some of my friends:

> So, math/physics people: If you have a 75 kg object falling at 9.8
> m/s^2 [gravity] what is the time till impact when dropped from 1, 2,
> 3m? What is the force of impact? If you need a decelleration time, try
> .1 sec. The answers people are giving me are far from what I expected,
> and I'm struggling through online physics tutorials to try to figure
> it out for myself.
>
> Then the reverse: What force at what accelleration is needed to move
> the object up? Let's say .5, 1 and 1.5 m, since I am a white man, and
> cannot jump

Dave wrote:

s = 0.5 a t^2
t = sqrt( 2s / a )
v = at
P = mv
F = dP/dt

t1 = sqrt( 2/9.8 ) = 0.45s   v1 = 4.41m/s    P1 = 331N-s
t2 = sqrt( 4/9.8 ) = 0.64s   v2 = 6.27m/s    P2 = 470N-s
t3 = sqrt( 6/9.8 ) = 0.78s   v3 = 7.64m/s    P3 = 573N-s

Since all the momentum is given up in the inelastic collision, the force
of impact is, as you thought, just the momentum above divided by the
amount of time you assume for the deceleration.

Here's my thoughts on finding that time: when the object hits the
ground, the leading edge comes to a stop immediately, but the higher
parts are still falling.  That means there's a compression wave going
through the object.  The time it takes for the compression wave to go
from the bottom to the top must essentially be the deceleration
time--and this should just be the sound speed in the medium times the
height of the object.

As for moving things up, we have the same problem as above: for a short
interval, acceleration must be greater than g, but we don't know the
interval, and hence not the force.  But if it was you jumping, think
about the time it takes for you to go from a knees flexed position to a
knees straight, at which point you leave the ground.  Only during that
interval can you be exerting any force at all, and you might as well
assume it's constant.  After that, it's just ballistics.

Dave