how do we use the concept of gravity um or center of gravity versus Space of support uh into to our clinical practice one example Is How We Do how we perform a therapeutic transfer I'm using this concept of center of gravity and the base of support if you look at this uh figure um here this person's base of support uh in sitting on the chair is really the four legs plus uh two feet so the entire area is this person's bace of support if this person is is trying to stand up from sitting position then he needs to move the center of gravity forward so it creates some kind of unstable status then that will trigger some movement so in uh we you can try yourself when you're trying to stand up from a chair you have to bend over and to move your center of gravity forward so that you feel um the center of gravity is within uh the two feet not much uh to the chair area that you feel it's not stable then you can use the muscle strength to stand up right so using the same concept this person is trying to move her Center his center of gravity from one base of support to another base of support let's assume that he's trying to get out of the uh the car so he's moving his center of gravity uh from the base of support of the chair uh in the car to the wheelchair um so same thing a same concept that we can expect that when a person who's sitting on the wheelchair and then they're trying to stand up the position um matters so um if a person is sitting in the wheelchair the base of support is basically the the Caster or the front wheel and the back wheel uh touching the ground so the the base of support is here when this person is trying to stand up um we typically recommend that they scoop over so that um it's easier to move their center of gravity forward and uh um to the front um however if you look if you look at the feat's position right here it's very close to the from Caster if this person bend over um over the base of support that make him uh this person's center of gravity fall out of the base of support then this person may fall easily because uh the center of gravity is out of the base of support um we can we can ask this person to extend or expand the base of support so that when they're trying to stand up uh the center of gravity is still within the base of support however if we ask this person to uh say uh reach their feet forward but um they did it too much then again it's very hard for them to move their center of gravity you know to the border of the base of support so that make stand up um harder then they may actually fall back because of that so this is one person uh trying to stand up what if the caregiver or a therapist is trying to uh transfer uh their patient here so that's focus on the person who's helping um the transfer let's say therapist um the therapist need to bend over their body when their their patient is sitting on the wheelchair and that would increase the strength um strength of their back muscle then they may hurt their back muscle because of the poor uh posture because basically the center of gravity kind of move forward and outside of their body right so basically that put a lot of tension to their back muscle a better way to help a person to transfer is um we can stand closer to the person who's being transferred and this and the therapist or the caregiver lower their center of gravity so that it's closer to the base of support that in theory is much stable than uh when they bend over right so in this way uh we call it a good body mechanics they're protecting their uh the uh their back muscle by um using a good body mechanics and they uh use the concept of C gravity and a Bas of support to help this person transfer that's safe that decrease the risk of fall so what about wheelchair basically wheelchair provide a larger base of support and the weight of the wheelchair help lower the center of gravity so that the center of gravity is well project the projection of the center of gravity is well within the uh base of support so you using this concept we can see that a person's uh who's who's who's sitting on the wheelchair like we discussed um previously and this person's center of gravity kind of go uh upward and forward a bit compared to uh a person without the wheelchair right that that's now assume that another person uh with amputation or with uh lower extremity amputation you can see that uh um the center of gravity goes even higher so um that would increase uh the RIS of fall also you can see that without this body segment the center of gravity falls even posteriorly to the border line of the uh base of support of uh provided by the wheelchair so when there's a push then it's very easily for the center of gravity fall out side of the base of support then the fall may happen so same thing we can expect uh to this type of wheelchair uh we call it a recliner here um if this person using this recliner wheelchair you can see that the base of support is provided by the Caster or front wheel and the uh back wheel right here this person's center of gravity is well within the base of support when we recline the body you see that the center of gravity kind of Falls posteriorly but if we don't do anything this person's much stable because the cent of gravity is still within the base of support however if we give this person a push then the center of gravity will fall you know outside the of the base of support then uh it it is very likely that this person uh will fall so how can we do as uh you know the therapist we can ask the vendor or we can install a stopper uh to the back right here so that when this happen the stopper can stop uh the wheelchair from going even even uh further right that will be something when we prescribe the wheelchair then you know we need to think about how we can help this person to maintain uh a stable position another thing to consider is the position of the wheel or the Caster so you see here this person's um sitting on the wheelchair the base of support is provided by the uh um back wheel and the Caster the front wheel the Bas of support is this large when we move the Caster May CH may turn backward that would actually narrow the base of support that would you know cause some kind of unstable um um status because the narrow uh base of support what may happen is when the person is trying to pick up an object from the ground when that means they they're moving their center of gravity forward and if the Bas of support become narrow then it's very likely that they will fall forward right so this is something we need to educate our clients when they're using the wheelchair or uh we need to uh uh make sure that a proper training you know can be done so remember my earlier uh question about why curb hopping is so hard so to to be able to uh hop up uh the the curve we this person need to move uh the center of gravity uh backward to you know to the very border of uh the the base of support to be able to raise up the Caster but looking at this basically the base of support become very narrow because they lose a larger area of Bas of support that the person may uh fall easily right and to do so the person need to have a pretty good sensation and muscle strength strength to perform to maintain a a um a balance uh when the Bas of support is very narrow in this way but you may ask why does a person need to learn this you know not every place has this kind of barrier free environment so when there's none the person needs to um have this ability to overcome this kind of barrier or obstacle uh in life another example is if if a person is into Sport and their wheelchair user so um because of the sport require you know High movement right high frequency of movement so what we typically do is we can um widen the base of support by changing the direction of the wheelchair so that we provide a much stable um um position for the athlete uh to use right because of that and then the weight of the wheelchair help lower the center of gravity right um then we offer uh a much stable environment for the wheelchair user to uh do the ex uh do the exercise that they want to do but one thing we also need to consider because uh when they're into sports they need a lot movement right so typically this type of design doesn't have a good back support so you also need to consider if your client has a good trunk control um if they're into the sports if they don't have good trunk control uh you can choose to train if it's trainable or you can do another kind of uh um modification to help them um using the wheelchair in in a better way so that they can engage in the sports that they want to