Here is an article updating some suggestions on polarized cardiovascular and endurance training.
Here is an interesting study where researchers investigated the relationship between muscle length and the capacity to produce torque in isokinetic knee flexion and extension, through a functional range of motion, between younger and older men 62.7+/- 2.5 years.
What they found is that at more stretched positions, older subjects lose the capacity to generate eccentric knee extension torque. The researchers suggest that more studies are needed to assess the mechanisms involved and the relationship with muscle length.
Until more research offers some suggestions on how to deal with the implications of dealing with reduced eccentric torque, perhaps including some squatting type of exercise with emphasis on the eccentric portion of the lower stretched part of the squat range of motion, might be worth including in a training program. One additional consideration, is that more recovery time is needed when performing eccentric focused exercise.
Melo, Ruth C, Takahashi, Anielle C.M.,Quiterio, Robison J., Salvini, Tania F.,Catai, Aparecida M. Eccentric Torque-producing capacity is influenced by muscle length in older healthy adults
Journal of Strength and Conditioning Research. 2016 Jan;30(1):259-266
While sprint interval training and high intensity interval training create similar cardiovascular and metabolic adaptations compared to endurance training, no studies have identified the differences in response between sprint interval training and high intensity interval training protocols.
Here is an abstract from a study published in the Journal of Strength and Conditioning Research, January 2016 Dissimilar Physiological and Perceptual Responses Between Sprint Interval Training and High-Intensity Interval Training . Researchers analyzed the differences between HIIT and SIT.
They suggest that choosing high intensity interval training over sprint interval training would be their recommendation if an individual is seeking to burn slightly more calories, maintain higher oxygen uptake, and experience lower perceived exertion.
There are several studies that have shown that while there is little reduction in stride rate with ageing, there is a significant reduction in ground reaction force, GRF, stride length, and obviously, velocity.
In a study published in the January, 2016 Journal of Medicine and Science in Sport and Exercise, researchers looked at the relationship between ageing and running biomechanics. They report that the data in their study support previous work showing, lower GRF, stride length and velocity in old runners. They looked at 110 healthy male runners between the ages of 18-60.
They found that running velocity was inversely related to age.(r=-0,27, P=.005) On a year to year basis, the results showed that there was a reduction in stride length, but not stride rate, and that mechanical reductions at the ankle but not the hip or Knee correlated with age.
In my own typical training, I try to include plyometrics and bounding as part of my natural interval running/speed hiking, and occasionally include dedicated short training sessions utilizing springing and bounding. I don’t know how well it may work toward retaining running speed, but it is something I enjoy and seems like it should be effective.
Devita, Paul, Fellin, Rebecca E, Seay, Joseph F, Ip Edward, Stavro, Nicole, Messier, Stephen P
The Relationship Between Age and Running Biomechanics Medicine in Science in Sport and Exercise January 2016 vol. 48 Issue 1 pp 98=106