While more complex system, than a machine of engineering, our body adapts to the demands placed upon it throughout our life. One of the demands we can place on our body is the repetitive, cyclical loads of long distance running. Whilst our body craves weight-bearing stress to strengthen it's musculoskeletal system, our humanity still leads us down the inevitable trail of atrophy & ageing. Whilst we have some control to minimise this process, the process progresses nonetheless.
The biggest change in running occurs around our plantar flexor muscles. The calf is king when it comes to applying the propulsive forces of running, and to lose calf muscle mass has large repercussions for our own running strategy. This reduction causes a reduced ability to take large steps, increasing our reliance on the frequency of said steps.
While not absolute, the main biomechanical changes that affect running biomechanics with age include:
Reduced Step Length:
~ 13% reduction in step length between 20 & 60 years of age (Devita et al. 2016).
Masters runners demonstrate reduced peak propulsive & vertical forces.
Plantarflexors are the largest contributor to propulsion & vertical support (Hamner et al. 2016).
Concentric ankle power is strongly associated with peak propulsive force & stride length (Willy & Paquette, 2019).
Increased Stride Frequency:
~ 4% to 6% higher stride frequency in Master runners compared with young runners (Beck et al. 2016).
Stride frequency (cadence) is inversely related to step length (Willy & Paquette, 2019).
To maintain a given speed, reducing step length will cause an increase in stride frequency (cadence).
Decreased Ankle Power:
Concentric ankle power during running decreases up to 47.9% between 20 & 80 years of age (Devita et al. 2016).
This decline is NOT compensated with by greater contributions from the hip & knee (Willy & Paquette, 2019).
May be a protective mechanism to operate within the reduced capacity of the plantarflexor muscle-tendon unit to reduce potentially injurious loads.
Decreased Ankle & Knee Excursions:
Master runners exhibit a more flexed knee at footstrike & reduced ankle, knee & hip excursions with less vertical oscillation of COM during stance (Willy & Paquette, 2019).
Common strategy to make initial contact in greater knee & hip flexion when step length is reduced.
Results in less excursion of knee ROM from initial contact to midstance.
Reduced knee excursion ROM results in less dropping in the COM.
Decreased Calf Muscle Volume:
Critical qualities such as plantarflexor CSA/muscle mass & achilles tendon stiffness, decline with aging (Karaminidis et al. 2005).
Plantarflexor muscle atrophy very common with ageing.
Reduction in muscle mass or cross-sectional area reduces the ability of the plantarflexors to apply propulsive & vertical forces, reducing step length (Willy & Paquette, 2019).
Increased risk of calf strain & Achilles tendinopathy:
Achilles tendinopathy is the most common running- related injury experienced by the Master runner (Mckean et al. 2006).
When training loads exceed the maximal load capacity of the tendon.
Reduced tendon stiffness & plantarflexor muscle CSA reduces the potential tissue capacity to handle running loads.
High plantarflexor capacity & function protective against achilles tendon injury (Willy & Paquette, 2019).
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