What does Minimum Effective Dose even mean? And how could it apply to bike fitting?
Minimum Effective Dose is partially a pharmacological term which is the smallest amount of a drug that will bring about the desired effect. So if 10 mg of a drug will lower your blood pressure to a prescribed zone we don’t want to give you 20 mg because it might cause unwanted problems — perhaps not right away, but maybe months or years down the road.
In the same way, we can apply this idea to bike fitting. If mechanics on the bike are optimized by sliding the saddle forward on the rails 7 mm, then moving it 15 mm isn’t ideal. Again, there may not be severe problems created by this initially, but 2 years down the road after your body has compensated to this new position you might be faced with the problem of needing a shorter reach to your handlebars when you go to buy that new bike. Because we went farther than we needed to, and made it too easy for your hands to reach the bars; your body adjusted to this and now requires that short reach (at least partially — we can always make changes in our body but I’ll get into more of that in a bit). Too much of the right fix is still wrong.
In fact, in my years of bike fitting I’ve found that some bike fit changes, when done in the right dose, can be prescriptive and temporary. For instance, occasionally I’ve had clients benefit from a small amount of varus posting to their cleats on one or both shoes. It can correct the foot mechanics that caused their knee, hip, or low back pain. The client rides with this corrective measure under their cleat for anywhere from a few months to a year. When they return for a checkup on their fit I test them with and without the varus wedging. Sometimes there is no difference in their mechanics when we remove the varus wedge. What happened? Many times the minimum effective dose can help retrain the client’s mechanics. This varus wedge triggered a response in certain muscles by placing them in a position where they’re more likely to engage. This engagement added up over time and lead to them eventually not needing the varus correction.
Does this happen every time? Of course not, but it happens often enough to remind me of the importance of treating and managing only what’s required.
Another reason to apply MED: once changes are made usually about half the effects of that change are seen right away. The other 50-70% happens as the person rides in this position for the next few weeks. All the soft tissues go through adaptation phases and the CNS also writes a new motor plan to control this new position.
This happens on every single bike fit I do. (I include follow up appointments for my bike fits for a year so pretty much everyone comes back at least once, which is great, so I get to see this take place). When I finish an initial bike fitting appointment I always take a complete round of data with both the infrared motion capture and the saddle 3D pressure mapping so that we have a complete “After” picture of their position. Then they go out and ride for a few weeks. When they return, I again get a complete round of data on both systems. Even though they didn’t change a thing about their bike all of their measurements are now different. Generally, on an initial bike fit I like to see changes occur of around 30-50% towards the position and mechanics I want them to eventually have on the bike, because usually on this return visit a few weeks later they are often 80-90% of the way there now.
At this point I have to decide whether I’m going to change anything else about their fit. Sometimes further changes are necessary, but other times if we just leave things alone their body will continue to adapt and get the last 10-20% of change on its own. How do you know whether to leave it alone or change more? That’s a tougher question, but it has a lot to do with what level of functional mobility they are starting out with and whether they are a “fast adapter”. Simply put, some people have bodies that have tremendous capacity for changing their mechanics and learning a new motor plan; other people….well, let’s just say they struggle a bit more.
Finally, what is this “ideal” bike position or mechanics that I am aspiring to for each rider? It would make it really easy if it was the same for everyone. If I just tried to get everyone to look and fit their bike pretty much the same way, it would make things a lot simpler (for me at least), and a lot of bike fitters out there do exactly this. But doing this just creates more bike fit trouble, because of course we can’t jam everyone into the same mold.
Instead, the picture I have in my head for each bike fit is different for every rider. Some clients will finish their fit almost exactly in the middle of all the “accepted” parameters for bike fitting, but most will end up towards one end of the spectrum or the other for some measurements.
For instance, a road cyclist that came to see me last week may be able to tolerate a 35 degree knee angle (measured dynamically of course — which is a higher saddle position) but needed a shorter bar reach (about 87 degree shoulder flexion), while another rider from the week before who is the same height and age needs a much lower saddle position (43 degrees knee extension) because they have tight hamstrings and lumbar spine but can tolerate a longer bar position because they have a longer torso and arms.
In fact, in some cases I will leave clients outside the range of what’s traditionally considered normal because their body and mechanics dictates it. Doing so leaves them in the most balanced position that their body is currently able to achieve….which brings me to my final point:
We can always fit our bike better without changing a thing on it. Every one of us has restrictions in mobility, strength deficits, and sub-optimal movement patterns. All of these things negatively impact how we sit on and move on our bike. Make the deficits smaller and the balance of the body greater and you’ll improve the range of possible postures you can maintain on a bike.
He lives with his wife and two kids and runs multiple businesses in Grand Junction, Colorado.