Biome­chan­ics

Here’s what sci­ence tells us.

Yoga Journal - - Contents - By Robyn Capo­bianco, PhD, and Jana Mont­gomery, PhD

Get expert anal­y­sis on the phys­i­cal im­pacts of jump­ing back to Plank Pose and Chat­u­ranga Dan­dasana.

AT SOME POINT, most yo­gis will be cau­tioned dur­ing Sun Sa­lu­ta­tions or vinyasas to “never jump back to Plank Pose—only to Chat­u­ranga Dan­dasana (FourLimbed Staff Pose). But this warn­ing doesn’t ex­ist in the fit­ness world, where jump­ing back to Plank is part of one of the most pop­u­lar body­weight ex­er­cises: the burpee.

This ba­sic exercise is sim­ple— start stand­ing; jump straight up; bend for­ward, and place your hands on the ground; jump back to Plank, then hop your feet to your hands, and re­peat. Sound fa­mil­iar? Elim­i­nate the ini­tial ver­ti­cal jump, add a back­bend (Co­bra or Up­wardFac­ing Dog) and Down Dog, and you have a clas­sic Sun Sa­lu­ta­tion.

Ac­cord­ing to Mark Sin­gle­ton’s book Yoga Body, it was Tiru­malai Kr­ish­na­macharya—the grand­fa­ther of West­ern yoga—who bor­rowed the jump­back to Chat­u­ranga from West­ern gym­nas­tics in the 1930s while he was de­vel­op­ing the sys­tem that be­came Ash­tanga Yoga. With most mod­ern forms of vinyasa and Power Yoga spring­ing from the Ash­tanga lin­eage, jump­ing back to Chat­u­ranga be­came wide­spread and is now in­cluded in most vig­or­ous yoga classes in the West. But given the shoul­der and wrist in­juries that are emerg­ing lately, it seems like a good idea to re­visit a few com­monly cir­cu­lated mis­con­cep­tions about the biome­chan­ics of the tran­si­tion.

First, let’s look at one myth you’ve likely heard: Jump­ing to Plank is jar­ring on your joints, forc­ing your wrists, el­bows, and shoul­ders to ab­sorb shock that would oth­er­wise be dis­persed by bend­ing the el­bows into Chat­u­ranga. This mis­con­cep­tion seems to be based on the false premise that be­cause Plank Pose is a bone-stacked po­si­tion, the lig­a­ments and ten­dons within your wrists, el­bows, and shoul­ders must ab­sorb more im­pact on the land­ing than they would in Chat­u­ranga.

How­ever, a 2011 study in the Jour­nal of Body­work and Move­ment Ther­a­pies showed that the mus­cles around your wrists, el­bows, and shoul­ders have to pro­duce more torque (a ro­ta­tional force) in the Chat­u­ranga po­si­tion (with bent arms) than in Plank Pose (with straight arms). This find­ing also holds true for jump­ing back to th­ese poses. Think about it: When you jump back to Plank, your shoul­ders stay stacked above your wrists, and your el­bows stay

rel­a­tively ex­tended or straight, which means the mus­cles around your el­bows don’t need to pro­duce as much torque as they would for a Chat­u­ranga land­ing. In­stead, the larger (and in most bod­ies, stronger) mus­cles around your shoul­ders and back con­trol the move­ment, which makes you less sus­cep­ti­ble to in­jury in your shoul­ders, el­bows, and wrists.

An­other mis­con­cep­tion about land­ing in Plank Pose is that the bone-stacked po­si­tion leads to lig­a­ment strain. Strain is sim­ply a change in length from an orig­i­nal state—a.k.a. a stretch. So, when you stretch your body, you ex­pe­ri­ence strain, which means strain it­self is not syn­ony­mous with in­jury.

In­jury oc­curs when you stretch your tis­sues beyond their ca­pac­ity to bounce back. For ex­am­ple, when you bend your el­bows into Chat­u­ranga, the lig­a­ments and ten­dons cross­ing the joint have to stretch. Lig­a­ments and ten­dons only un­dergo strain when a joint is flexed or hy­per­ex­tended—not when bones are stacked. In Plank Pose, the lig­a­ments and ten­dons cross­ing the el­bow joint don’t change lengths—which means they aren’t strained.

Fi­nally, you’ve also likely

heard the myth that jump­ing back to Plank Pose is harder on your lower back than land­ing in Chat­u­ranga. It’s true that if your core isn’t en­gaged when jump­ing back to ei­ther Plank or Chat­u­ranga, your lower back can sag. This, in turn, can com­press the facet joints—the points of ar­tic­u­la­tion be­tween the ver­te­brae that al­low your spine to flex and ex­tend—and lead to bone de­gen­er­a­tion if done re­peat­edly over time.

On the flip side, if your back is over-rounded on ei­ther land­ing, your ab­dom­i­nal mus­cles can create too much torque on your ver­te­brae, which can lead to com­pres­sion in the discs, re­sult­ing in in­jury. Pre­vent ei­ther sce­nario by jump­ing back to ei­ther pose with an en­gaged core, which will keep your spine neu­tral.

En­ter the biome­chan­ics lab

When we weren’t able to find sci­en­tific re­search ex­am­in­ing the biome­chan­i­cal dif­fer­ences be­tween both tran­si­tions, we headed to the Ap­plied Biome­chan­ics Lab at the Univer­sity of Colorado, Boul­der, to in­vesti- gate. The lab has a 10-cam­era mo­tion-cap­ture sys­tem and spe­cial plates that record

ground re­ac­tion force— the force the ground ex­erts onto the body in re­ac­tion to body weight ex­ert­ing force onto the ground.

We placed sen­sors on a yogi’s hands and lower back as ref­er­ence points to de­ter­mine where the cen­ter of gravity moved dur­ing th­ese two tran­si­tions. The ver­dict: Peak ver­ti­cal ground re­ac­tion force— the high­est ground re­ac­tion force in the ver­ti­cal di­rec­tion— was equal for both tran­si­tions (about 1.5 times body weight). That means nei­ther land­ing can ac­tu­ally be clas­si­fied as more jar­ring.

In fact, the peak ver­ti­cal ground re­ac­tion force in both jump­backs was closer to that of walk­ing (1.3 times body weight) than run­ning (2.5 times body weight). That means that with the re­quired strength and proper form, jump­ing back to ei­ther Plank Pose or Chat­u­ranga pro­duces only a slightly higher im­pact on the body than walk­ing.

Next, we did some fol­lowup test­ing to mea­sure the ground re­ac­tion forces on the

sub­ject’s hands and feet sep­a­rately dur­ing both tran­si­tions. As it turns out, jump­ing back to Chat­u­ranga re­sulted in a ground re­ac­tion force at the up­per body that was 10 pounds more than jump­ing back to Plank (7 per­cent of the model’s body weight). Yet the re­verse was true when jump­ing back to Plank: It was eas­ier on the shoul­ders and wrists, but slightly harder on the feet— about ad­di­tional eight pounds of ground re­ac­tion force (5 per­cent of the model’s body weight).

Per­haps our most im­por­tant find­ing was that the cen­ter of gravity stayed closer to the hips in the jump­back to Plank and moved about four inches closer to the head in the jump­back to Chat­u­ranga. That means, when com­bined with ground re­ac­tion force, more body weight has to be sup­ported by the arms in the jump­back to Chat­u­ranga, which in­creases the amount of torque your shoul­ders, el­bows, and wrists must pro­duce in or­der to land and main­tain safe joint po­si­tion­ing in Chat­u­ranga. The more mus­cu­lar force re­quired, the more op­por­tu­nity for in­jury—par­tic­u­larly at the joints if the mus­cles around them can’t pro­duce enough force to land or hold Chat­u­ranga.

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