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The cycling kinetic chain
In part 1 of this series, we introduced the concept of “Mastering Load” in cycling, essential knowledge for treatment and injury management, with its inherent requirements being a knowledge of:
Whilst we have touched upon the lack of ‘conversation’ regarding the cycling kinetic chain and its relationship with injury, there have been informed commentaries in the past eschewing a kinetic chain approach:
Gregor, in his classic review paper of 1996, commented “knowledge of….load sharing among all segments responsible for the co-ordination of energy delivery to the crank is important..”
In that same review he quoted Van Ingen Schenau, 1989,
“…uniarticular muscles are power producers and bi-articular power distributors….”.
FACT: The kinetic chain approach to analysing pedalling is a viable construct
As a background I think we must explore the “Perfect” vs “Imperfect” technique of pedalling, and how this imperfect technique can be a source of pain or injury. And what the measures are which guide us in assessing that a pedal stroke is imperfect – kinematics, muscle activation, co-ordination, strength, length-tension relationships, force, power, posture?
In the area of normal muscle activation in the pedal stroke, the historical perspective was simplistic, with the more realistic pattern represented in figure 1
(TDC = top of pedal stroke; BDC = bottom of pedal stroke)
And whilst the gluteals and quadriceps are seen as the main muscles for power production, co-ordination of the pedal stroke utilizing the hamstrings and calves seems an important feature of “perfect” pedaling (Blake 2012).
Note the extensive range of hamstring activation, as well as the calf, especially in the power phase, in an agonist/antagonist relationship to control the pedal stroke. Also the activation of tibialis anterior, and vastus lateralis and medialis, at the end of the recovery to prepare to push over the top of the pedal stroke.
The most efficient pedaling needs to maintain power at the top and bottom of the pedal stroke (Dead Centres – Leirdal 2011). Given that the peak of power is at 3 o’çlock on the clock-face, maintaining power at the Top Dead Centre (TDC) and Bottom Dead Centre (BDC) becomes a challenge of co-ordination/activation.
Blake (2012) looked at muscle co-ordination patterns in cycling, finding that peak efficiency occurred at 55% VO2 max, with efficiency being the relationship between power output and metabolic cost. At optimal efficiency there was an even spread of activation levels between the muscle groups, but as the workload increases, there was a greater emphasis upon the power muscles (GMx, VL, VM), and less efficiency (least at 90% VO2 Max), with a higher level of variation in the timing of the co-ordination muscles (Hamstrings, RF, Gastrocnemius).
Blake showed that the GMx and VL/VM are the power muscles acting vertically, but with the VL/VM activating earlier in the pedal stroke at higher workloads, and GMx increasing the most relatively, as workload increases. An increase in the work done by the power muscles relative to the co-ordination muscles is a common theme with increased workload and fatigue states (Dingwell 2008, Bini 2010).
Periods of high workload (hills/powering) and fatigue have a relationship with the clinical presentation of pain in the cycling community. Rarely does pain present in “easy” riding.
The GMx has the greatest potential for increased power as it functions at low MVC at maximum efficiency. One can imagine it, and the VL/VM being the gears, and the co-ordination muscles the clutch, allowing for synchronous change in gears and timing of activation. So the “gears/power muscles” increase their activation level significantly with increased workload, whilst the co-ordination muscles don’t increase their activation for power, but they function for smooth transmission of the power, especially in the TDC/BDC positions.
The idea that the hamstrings and calf muscles work synergistically with the power muscles to co-ordinate the fast and powerful moments of hip, knee and ankle extension resonates well from a movement analysis perspective, with early activation of quadriceps and tibialis anterior at TDC to gain a good angle for the horizontal vector component, also a notion that makes sense. Add the strong and smooth transmission of force to the pedal through ball of foot contact and good foot and ankle range and position, and the proposed model of power and co-ordination presented by Blake is highly usable for the physiotherapist in optimising efficiency and injury prevention in cycling.
The co-ordination correlate on the bike is high cadence pedaling (100RPM+), with riders who struggle with their co-ordinative muscle activation finding it difficult to maintain a smooth pedal stroke and “bouncing” around on the seat. Practice of high cadence pedaling is common in well-trained cyclists – therefore the practice of optimising co-ordinative patterns exists.
So the higher the workload, the more dominant the power muscles become, with a less efficient and more vertical pedal stroke. If the power muscles are deficient other muscles must fill the gap as workload and fatigue increase. Riders with poorer co-ordination will use the power muscles more at lower loads, with earlier fatigue, less efficiency and greater potential for adverse kinematics.
FACT: There is a “more perfect” way to pedal which may influence injury risk.
As a clinician analyzing the cycling kinetic chain for a relationship between pain/injury and a posture, movement or strength parameter, one soon realizes that the evidence is minimal and not strong.
We look to use the evidence base, to extrapolate from “on-land” activity theory, to use performance based knowledge, and clinically reason the findings of a thorough assessment in best practice management.
Extrapolation to Land based presentations:
Performance based parameters:
FACT: Plumb Line measures and fore-aft seat measures are not represented in the evidence.
It would seem that key features of the CYCLING KINETIC CHAIN are lumbar spine position, degree of lateral pelvic tilt, gluteal and quadriceps muscle ability, degree of knee valgus (splay), the ability to be smooth and co-ordinated in the pedal stroke, knee angle at BDC, ankle DF angle and ankle joint ability and the point of force application foot to pedal.
Pain and injury in the athletic population is complex in its aetiology. Clinical reasoning is essential to optimising management, and in cycling understanding the knowledge base regarding the interaction between the body and the bike is an important cornerstone to expert practice. The kinetic chain approach to analysis of cycling injury is a valid pathway and will bring cycling injury management to a level similar to other high performance sports.
Want to know more?
Join us at our Science of Cycling course on 26 & 27 October 2019. Email firstname.lastname@example.org for a registration form.
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PART 3: Training Load and Injury : A coaches perspective