Leg Smoothness

Leg Smoothness is an MPI that shows how smooth your thigh movements are when pedaling.

Overview

• Measure the smoothness of the thigh movement from the uppermost position of the knee to the lowermost position of the knee.
• Lower scores indicate a more efficient thigh movement, with zero being the most efficient score.
• The lower the score and the smoother the thigh movement, the less energy is wasted.

Why Leg Smoothness is important

When pedaling a bicycle, the repetitive motion of the lower limb is performed with two fulcrums. The first fulcrum is the contact point between the sole of the shoe and the pedal via the cleat. And the second one is the contact point between the buttocks and the saddle. The movement of the three joints between the two fulcrums, namely the hip joint, knee joint, and ankle joint, determines the lower limb form during pedaling, leading to productive power output to the bicycle.

Although the movements of the joints are mainly flexion and extension, the joints farther from the fulcrum have a higher degree of freedom, and joint changes on different axes such as adduction/abduction and internal rotation/external rotation are also possible. Concerning the form that produces productive power output, it is considered that these different joint movements are optimally linked depending on individual muscle strength and muscle balance.

One of the remarkable differences is the movement of the thighs. Mainly in the hip joint and knee joint, the movements of adduction/abduction and internal rotation/external rotation are observed more often rather than flexion/extension. This means that inefficient thigh movement may occur.

Therefore, it is essential to quantify and observe the movement of the thigh. Especially in the pedaling cycle, it is important to focus on the movement from the thigh top to the thigh bottom, which is the section where power is primarily generated.

One of the indicators of the efficiency of movement, that is, whether or not the maximum range of movement can be produced with less metabolic energy consumption, is an index of smoothness. LEOMO's Leg Smoothness MPI quantitatively evaluates that smoothness. Especially when pedaling a bicycle, as mentioned above, the score will focus on the movement from the thigh top to the thigh bottom.

 

About Leg Smoothness MPI Score

• To express the smoothness, there is a physical index called a jerk, which is the time derivative of acceleration. Leg Smoothness MPI quantitatively evaluates smoothness using the jerk and shows it as a score. The larger the jerk, the less smooth it is and the less efficient the movement. Jerk is commonly used not only as a physical exercise but also as an index of the smoothness that humans feel in a moving body such as a passenger car. It can also be used to measure physical exercise efficiency other than bicycles, such as running.

• As shown in the chart below, the sensor attached to the front of the thigh near the knee is used to calculate the jerk in the rotational direction on the horizontal axis around the hip joint, not strictly downward to the ground.

Also, the thigh movement smoothness in bicycle pedaling should be evaluated by a normalized index that does not depend on the difference in cadence or the magnitude of power. LEOMO's Leg Smoothness MPI is a score that considers these condition changes, that is, is not affected by these changes. Therefore, it is also possible to compare scores between different cadence intervals and different power menus. It is also a confirmation indicator of forms affected (or not affected) by various conditions.

For example, you can compare the smoothness of a low load and low-power output state with a low gear and the smoothness of a high load and high-power output with a high gear on the same scale. This makes it possible to quantitatively evaluate how smooth the thigh movement can be maintained in a progressive effort that gradually increases from low load to high load and low power to high power.

Leg Smoothness	Level	Visual Reference
< 5%	Very smooth	No acceleration/deceleration in a leg movement
5 – 10%	Moderately smooth	Moderately efficient leg movement
10 - 15%	Moderately uncoordinated	Less efficient leg movement
> 15%	Jerky	Inefficient leg movement

Note: The correct score may not be obtained if vibrations other than the normal pedaling motion are transmitted to the thighs and knees due to road conditions.

Underlying LEOMO Theory

Here we explain why observing and understanding the MPIs are important, given that the upper body above the saddle can be fixed.

First of all, even if you can effectively use the posterior muscle group, the power output transmitted to the bicycle will eventually be the pedal contact. Therefore, the movement of transferring a series of forces from the posterior muscle group to the pedal is critical. The vital action here is Triple Extension. It is necessary to transmit the output generated at the hip joint to the pedal through the knee joint, ankle joint, and pedal shaft. It indicates the usage of these three joints, that is, the coordinated movement of extension, flexion, and lock.

The concept of triple extension is not difficult to understand in biomechanics. It is a simple idea to extend and lock the joints to effectively transmit power from the posterior muscle groups to the pedals through the thigh hamstrings and the calf posterior soleus muscles. Rather than moving each joint independently, it is more efficient to transmit more force from the hip joint to the knee to the ankle in order. There are research results that show that the force generated above the knee and transmitted to the ankle is six times as different when interlocked and disjointed. The muscles from the buttocks to the back of the thighs occupy more of the body. Therefore, it is essential to extend these parts in any exercise, not just in the bicycle.

If the knee joint and ankle joint are locked while the hip joint is extended, or if the force can be applied by further extension, it can be said that the posterior muscle group can be utilized to the maximum extent. However, in a bicycle, the thighs are lowered during hip extension. If the knee joints or ankle joints bend during this period, the power will be lost. If you bend these joints, you will see a significant change in MPI value. Specifically, the DSS tends to increase, and the FAR and FAR(Q1) measurement values ​​also tend to increase.

Even with these three MPIs, it is possible to measure the efficiency of triple extension in pedaling, but because it uses a foot sensor, that is, from the waist, via the hip joint, knee, ankle, and three joints. Therefore, there are some other factors associated with the score. Even if it is not due to inefficient triple extensions, it may not be likely that these MPI numbers will be high.

So, what LEOMO focuses on was the change in the acceleration of the thigh movement. The triple extension can be evaluated more directly by observing the change in thigh acceleration closer to the joint that produces the maximum output. When one of the joints bends, and the force is wasted, causing the force to escape, the thigh movements accelerate rapidly. On the other hand, if you extend the hip joint more than necessary and alienate the extension of the hip joint, the thigh movement appears as a sudden deceleration. In either case, the three joints are in a state where they are not efficiently linked, and in the end, the force exerted by the posterior muscle group cannot be efficiently transmitted.

As shown in About  Leg Smoothness MPI Score, Leg Smoothness can be said to be a generalized triple extension evaluation index because the thigh acceleration changes are normalized regardless of fluctuations in cadence and power.

Sensors

• Thigh placement

• Use Adhesive tape

• Attach to the front of the thigh, not the side.

• For best results, place the sensor at least 10 cm from the knee or the hip.

Real-time data & analysis

Thigh Swing Speed can be observed in real-time.

Coaches can access the scores in real-time with LEOMO LVS.