Speaking to cousin colin the other day i was speaking about the benefits of riding with clipless pedals. I guessed that he might be losing up to a 1/3rd of his power by just using platform pedals … that was a guess so i delved a bit deeper …
this from triathlon resource
Improving your pedal stroke efficiency is one of the most effective ways to improve cycling performance. The human body was made to walk and run, not to pedal a bicycle. I have performed or supervised over 6,000 VO2 Max tests. The results clearly and consistently indicate that pedal stroke efficiency is a key limiting factor for performance athletes. For example, an elite cyclist may produce 20% greater wattage than an intermediate, but consume only 8% more oxygen to do so. In other words, the elite is only 8% fitter and the remaining 12% increase in wattage may be attributed to more efficient pedal stroke mechanics.
On a flat road, the momentum of the rider’s weight moving at a fairly high speed will pull him through dead spots in his pedal stroke, so on flat roads a powerful rider with excessive dead spots in his pedal stroke can “coast” through those dead spots. At the slower speeds cyclists use to climb hills, the rider’s momentum is not so great a factor. Gravity tugs continually and, without momentum to smooth over the dead spots, riding speed literally slows between each pedal stroke. Much of the power generated by each pedal stroke is then wasted on accelerating back to the original speed instead of going faster up the hill. If you are stronger on flat rides than on hilly rides, even when taking bodyweight into account, your pedal stroke probably needs some work.
Cyclists are often told to develop a circular pedal stroke. However, the human body cannot produce a perfect 360-degree pedal stroke and even the most efficient cyclists fail to create power anywhere close to evenly throughout the circle. Our research has shown that the greatest pedaling efficiency occurs by imaging pedaling triangles instead of circles. Mentally breaking the pedal stoke down into the downstroke, the backstroke, and the upstroke and attempting to create power in three straight lines, produces the closest to a circular pedal stroke that a cyclist can create. It also yields the greatest wattage for the amount of oxygen consumed. Taking the time and effort to work on each of these three parts of your pedal stroke will pay big dividends on race day.
Most of a cyclist’s power is derived from the downstroke. Even a very smooth pedal stroke that lacks power in the downstroke is not efficient.
The quadriceps and the gluteus maximus muscles, two of the most powerful muscles in the body, both provide significant power on the downstroke. One key to the downstroke is creating a long power zone by maximizing the period during which these muscles contract simultaneously.
Good cyclists lengthen their power zones at the top of the pedal stroke, applying pressure earlier in the stroke. Less efficient cyclists try to lengthen their power zones at the bottom of the stroke, which only wastes energy. We recommend concentrating on beginning the downstroke at 12 o’clock and driving diagonally down toward 3 o’clock.
Most of a cyclist’s power is released during the down-stroke. This phase of the pedal-stroke, when performed properly, overlaps power output from hip extension (gluteus maximus and hamstrings) and knee extension (quadriceps). Misunderstanding how power should be applied during the down-stroke causes many riders to lose this crucial overlap and overuse the hamstrings.
The second key to the downstroke is unloading pedal pressure before bottoming dead-center. Since the downstroke is such a naturally dominant part of the pedal stroke, cyclists continue to push down even when the crankarm is at the very bottom in the 6 o’clock position. Obviously this does not contribute to propulsion, but it does waste energy as well as causing muscular fatigue and saddle discomfort. While even the best cyclists in the world fail to completely unload at bottom-dead-center, efficient cyclists come closer than less-skilled cyclists. Working on this skill reduces wasted energy. Transferring smoothly into the backstroke phase of the pedal stroke minimizes energy wasted at bottom-dead-center. The key is attempting to begin the backstroke phase early.
Many cyclists begin the down-stroke late, at about 2 o’clock and direct their power directly downward. This minimizes the overlap of the optimal torque ranges of hip extension and knee extension and may call the hamstrings into play excessively. Since the quadriceps muscles are not activated properly, almost all the power must be produced by hip extension. To accomplish this, the hamstrings must create a very forceful contraction.
In an ideal down-stroke, the power application begins early, at 12 o’clock, and is directed downward diagonally toward 3 o’clock. This activates the quadriceps optimally and lengthens the overlap between the peak-torque production of knee extension and hip extension. The quadriceps and gluteus maximus are the primary power producers and the hamstrings contract moderately.
A moment of crisis arises during each pedal stroke when the pedals are at the 6 o’clock and 12 o’clock positions and neither leg is engaged in the downstroke. While little power is generated at this point in the pedal stroke, creating as much as possible is critical, especially for climbing. The goal is to provide just enough power to maintain momentum until the next downstroke begins.
Most cyclists don’t really have a backstroke phase, because their downstroke phase lasts too long. We recommend trying to pull your heel back directly through the bottom bracket, beginning at 3 o’clock. Obviously, this movement is impossible, since the crankarms don’t allow it, but attempting it triggers an early backstroke and minimizes wasted energy from pushing down at bottom-dead-center. The downstroke is such a naturally dominant part of cycling that thinking in terms of prematurely pulling straight back actually produces a more circular down/back movement. Attempting to pull back at 3 o’clock will not reduce the power of the latter stages of the downstroke. The leg will, in fact, continue to produce downstroke power well beyond 3 o’clock. However, attempting to begin the backstroke early prevents the downstroke from lasting too long and increases he efficiency of the stroke.
The backstroke is one area of the pedal-stroke where the hamstring muscles should be very active, because only knee flexion provides power in this range. Relaxation during the ranges of the pedal stroke in which the hamstring muscles should not be used heavily (upstroke and downstroke) prevents fatigue and enables powerful backstroke contractions.
The primary pedal-stroke weakness of many riders is extending the down-stroke too long and starting the backstroke late. This prevents the rider from unloading before bottom dead center and causes wasted energy pushing downward when the crankarm is moving directly backward.
When you were first learning to ride a bike as a kid, what type of pedals did you use? Like everyone else, you used platform pedals, which require different biomechanics than clipless pedals. Have you ever made the effort to learn about the differences?
On platform pedals, how do you keep your right foot on the pedal while your left foot is pushing down? You push down a little bit. This is terribly inefficient, actually using energy and fatiguing the muscles to create negative power. Since you began riding with clipless pedals, have you implemented changes in your power application? Or, like many cyclists, even pretty good ones, do you still pedal the same way you did as a kid, only harder and longer?
At steady riding speeds, even the world’s best riders don’t create power on the upstroke. The difference is that they do not create negative power, while most beginning and intermediate riders do. The goal of the upstroke is to unload the pedal, lifting the weight of the leg, foot, and shoe off the pedal. This allows all of the power generated by the opposite leg’s downstroke to be delivered to the rear wheel and provide propulsion.
Most cyclists create negative power during the upstroke, actually allowing the left leg’s downstroke to lift the weight of the right leg, foot, and shoe. This negates some of the power generated by the downstroke.
Efficient riders may actually produce significant upstroke power during periods of very hard pedaling, such as on very steep climbs. During steady state riding, however, efficient riders simply lift the weight of their foot, leg, and shoe during the upstroke, but do not create power during this phase. We call this “unloading”. This aspect of pedaling is critical. Consistent unloading on the upstroke is one significant difference between elite and intermediate riders. Without correct unloading, the right and left legs actually fight against each other.
The movements of the upstroke are hip-flexion (lifting the knee) and knee-flexion (lifting the foot). Since the hip-flexors are active only in this range of the pedal stroke, they should be the primary muscle contracting during this phase. The hamstrings are very active during the backstroke and somewhat active during the downstroke, so efficient riders relax them during the upstroke. Triathletes must also come off the bike with relatively fresh hamstrings in order to run well.
Attempting to pull up on the pedal through this phase places too much concentration on knee flexion and prevents hamstring relaxation. The hip flexors, once trained, are extremely fatigue resistant. They are only active for about 25% of the pedal stroke. Obviously they can contract fairly powerfully without fatigue when their work to rest ratio is 1:3.
There are two keys to taking advantage of the fresh hip-flexor muscles and resting tired hamstring muscles during the upstroke phase. The first is keeping your concentration on lifting the knee and not the heel or the foot. If a cyclist lifts his knee powerfully, the foot and pedal will follow without contractions to bend the knee. The second key is thinking of the upstroke as a diagonally upward and slightly forward movement, instead of an upward and backward movement. Again, this places the emphasis on the hip-flexor muscles, which should be contracting, instead of the hamstrings, which should be relaxing. When your pedal reaches the seven o’clock position, think of driving your knee up toward the handlebar.
this from Livestrong …
Cycling is an effective low-impact cardio workout, a popular sport and also a method of transportation for much of the world’s population. Whether you pedal a mountain bike up steep tracks, a track bike around a banked velodrome or a stationary bike in an indoor cycling class, the muscles that are used are much the same.
Much of the power for cycling comes from the hips. The gluteus maximus and hamstring muscles contract to drive your femur or thigh bone downward. Meanwhile, on your opposite leg, your hip flexors — the iliacus and psoas muscles — contract to pull your femur upward. Using pedal cleats can help these muscles work more efficiently and allow you to generate more power. In addition, the muscles on the inside and outside of your thigh — the adductors and abductors, respectively — work to keep your hips properly aligned.
Your knees work very hard during cycling. It is often the muscles that cross the knees that you can feel working the hardest on a long sprint or climb. On the front of your thigh, your quadriceps contract to extend your knee and drive the pedals downward. The most active of the four quadriceps muscles is the vastus medialis located just above and to the side of your knee cap, although your other quadriceps muscles are also very active. On the rear of your thigh, your hamstrings work to pull your foot backwards. Cleated pedals or toe-straps allow you to exert a greater force when pulling the pedals backward and help to increase power transference.
Active pedaling, also called ankling, is a technique used by cyclists to maximize pedaling efficiency by utilizing the muscles in the lower leg as much as possible. Pressing your toes down through the pedals uses your posterior calf muscles — the gastrocnemius and soleus. As one leg is pushing down, the muscles on the front of your opposite shin — tibialis anterior — pulls your toes upward. By using your ankles as actively as possible, you can increase your force generation, albeit only slightly.
When you are cycling on flat roads at a moderate pace, your upper body does not play a very active role. This changes when you get up and out of your saddle to climb a steep hill or sprint. As you increase the pressure on the pedals, your upper body is called upon to counterbalance the efforts of your legs. The main upper-body muscles used in climbing and sprinting are your biceps, triceps and latissimus dorsi. Located on the front of your arm, back of your arm and side of your back respectively, these muscles generate downward force so you can develop increased pressure on your pedals. In addition, the muscles of your core work hard to stabilize your spine and ensure that the efforts of your upper body are transmitted efficiently to your legs.