Perform a (not so) Basic Bike Fit | Joint Landmarks | Part 2
Bike Fit Landmarks
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This is where our basic bike fit becomes more than that. Setting accurate landmarks will make our measurements easier and more accurate simply because we'll have the best idea possible of where to lay our joint angle lines.
It really pays to have a better understanding of the anatomy to do this. At least a basic knowledge of anatomy will be very helpful -- knowing the proper names of the major bones of the body along with a basic understanding of muscle structure is ideal. The greater your understanding of this anatomy, the better you'll be able to "see" the bones and other tissues through the skin. I often liken it to having x-ray vision since as you palpate certain structures you have to imagine where the adjoining tissues and bony structures lie in order to make locating the landmarks properly very easy.
As we go through the palpation process, the end goal is being able to accurately approximate the centers of rotation of the joints. The center of rotation is the pivot point around which the movement occurs, and so when figuring joint angles, the better your landmark placement -- i.e. the closer you are to the center of rotation -- the better your data will be. If you have poor placement of a landmark then your data will have a significant margin of error making it difficult to draw any meaningful conclusions from it.
In the video analysis apps we'll use the joint landmarks to get the joint angles. For example, if we draw an angle starting at the hip joint, going through the knee to the ankle, this will give us our knee angle measurement. The apps will provide dots or circles at the joint landmarks, but we're not going to just rely on placing those over the video -- we're going to stack the deck in our favor for accuracy and place landmarks on the rider themselves to use as reference points to make it easier to find the joint centers on the video.
The reason we don't rely just on the video is simply mathematical -- without on-the-body landmarks already tagged, we're relying on picking out the proper landmark location on a relatively small screen. If you're using the app on a 10" tablet, the overall size of the rider is very small -- perhaps just 7 or 8 inches large. On your phone it's even worse. Even on a large desktop display - let's say you have a 50-inch screen - the rider on the screen is only going to be perhaps 24 inches tall.
Would you rather try to find these landmarks on a 2-foot tall screen image or on the actual 5'10" frame of the actual rider?
Discerning a joint landmark from this tiny on-screen figure is possible but the likelihood of exactly nailing the joint center is much lower when compared to putting a sticker or dot on the full size person beforehand.
This becomes especially important if you're stuck with a recording that was shot at a slower frame rate -- like those at 30 fps -- there's a very good chance that one or more of the joints you're trying to analyze will be blurry. Having the joints marked with contrasting adhesive dots will make it more likely you'll be able to approximate where the joint is in that blurry frame. The higher the frame rate, the more crisp and clear the paused video will be and therefore the easier it will be to see the pre-tagged landmarks.
I like to find all the lower extremity joint landmarks with the rider's leg positioned in the 3 o'clock position. Why? Simply, it's the middle of the power phase of the pedal stroke and therefore provides the best "average" of each joint's location at any point in the stroke.So now let's move on to the "how to" of locating these landmarks:
Ankle
We'll address the easiest landmark to find first. The center of motion for the ankle coincides with a very easy landmark to palpate -- the lateral malleolus. The lateral malleolus is the prominent bump on the outside of your ankle. Generally this bony structure stands out quite prominently and so finding the center point of it is a simple task. We can place our marker on the center of this prominence to locate the center of rotation of the ankle.
Knee:
basic bike fit |locating the knee landmark
basic bike fit
Here's a brief video that reviews the main points to accurately locating the knee landmark:
Password: knee dot
Begin by finding the kneecap -- "pinch" it between your thumb and forefinger from top to bottom so that your thumb rests on the inferior point and the forefinger on the top of the patella where the quadricep tendon attaches.
Here's a view with some x-ray vision built in:
basic bike fit
Bring the thumb along the knee down slightly and back (towards the rear of the rider) until you feel a little step or recess. In some people there will be a soft patch of tissue here because there is a infra-patellar (below the knee cap) fat body. This is just above the the lateral aspect of the tibial plateau. Now drag the thumb just a few millilmeters further back along the joint line and then superiorly about a centimeter or less and you might feel a small bump on the outer aspect of the knee which is the lateral femoral condyle. This is a pretty good location for your knee marker as it approximates well the center of rotation of the knee. If you don't feel a prominent bump, it's okay, just approximate the location just above the joint line.
Hip
Here's a brief video that reviews the main points to accurately locating the hip landmark:
Password: hip dot
Accurate placement of the hip dot requires more practice than other landmarks because there's often a lot of soft tissue in the way. In some riders, often men, the bony landmarks are very prominent and easy to locate. The main landmark we're looking for is the outermost portion of the greater trochanter of the hip. A trochanter is a bump or "bony protuberance", on the outside of the femur, and it only represents an approximation of the center of the hip joint. The difficulty with locating the actual hip joint is that it lies very deep -- imagine the intersection of a line going directly in from the side just above the greater trochanter and another from the front right through what we think of as our groin. Roughly where these lines would intersect is the location of the actual ball and socket joint of the hip. The socket itself is actually part of the pelvis and so lies very deep.
To properly locate the hip dot begin just by palpating the outside of the hip in the general location of the greater trochanter. It's difficult to do this localizing palpation with fingertips and you might have more success using the palm of your hand flat on the hip. Using the palm this way is often easier to differentiate between density differences in the tissue below. Since we're looking for a bone in a sea of fascia, muscle and fat, using the flat of your palm can make it a lot easier. Once you have a basic location, then switch to fingertips and probe gently into the tissue around the greater trochanter -- don't try to hit it directly with fingertips as you're likely to lose the sensation of it. Remember the greater trochanter, like most bones in our body isn't a flat structure, it's rounded or domed and so when you try to put your fingers directly on it you can easily roll off the side and misplace the marker. Instead think of trying to pinch around it so that you have the entire trochanter between your thumb and forefinger as in the picture below.
basic bike fit
Often it's easier to define the borders of the greater trochanter to discern it's center point than it is to try to locate the center directly. As I mentioned sometimes it will be very easy to locate in thin or muscular individuals. Occasionally, though, even in these very fit people it might be a challenge because of the resting tension in the gluteal muscles, fascia and tensor fascia latae muscle immediately surrounding the hip bone.
Additionally in some rider's, both men and women, there will be a layer of fatty tissue in the way. This is when using the flat palm to generalize the location is beneficial, but you may need to use additional tricks. One simple method is to have the rider move their knee side to side slightly. This will move the trochanter back and forth under your fingers and this can help you get a starting point for it.
In the next installment (Part 3 is here) we're going to go over some of the data from our measurements and what they mean for bike fit changes. You'll learn when to change saddle position (raise, lower, fore, and aft movements) and begin to learn about how bar position relates to saddle placement. The reason we address saddle position so deeply is because bar position is predicated on it -- if you don't get the seat right, the bar won't be optimized.