Long and Strong suggests the fascicle length of muscles while undergoing load eccentrically. An accelerated program whereby early load is implemented (even if it is just 1 or 2 simple eccentric exercises), strength gains and fascicle length is developed quicker (Hickey et al, 2017). Loading often regards to following rehabilitation protocols which require a minimum of 6 weeks loading principles and rehabilitation. When returning to running, it is important to increase distances and speed at the rate the physiotherapist sets however, the optimal goal is to maintain speed when sprinting and in return to sport.
The aim of “longer muscle strength” (eccentric) is that there is sufficient evidence to suggest that there is a direct link to reduced re-injury by maintaining healthy fascicle length and peaks in torque and activation levels. By maintaining these factors at a higher level subsequently, risk factor levels drop. By improving the function of the hamstring, the demand of the quadriceps (i.e. front of the leg) reduces and further anterior knee injuries reduce by balancing the quadricep to hamstring ratio.
How can I improve these risk factors and what is the BEST exercise:
The Nordic Hamstring Curl exercise has been shown to significantly reduce hamstring injury rate by specifically targeting the improvements in the aforementioned muscular architecture above. It has a proven re-injury rate reduction by 85% (Peterson et al, 2011).
How? Studies have shown that when comparing this exercise against a resisted hamstring curl, variables of (1) strength, (2) power and (3) voluntary activation is higher when performing an eccentric strength program (Marusic et al, 2020). However, challenges include the requirement to add load to the exercise to raise the exercise from sufficient to desired outcome, with studies suggesting that a low volume prescription (e.g. 3-5 repetitions x 1 set) is insufficient long term.
How can I challenge this? Effectively, weighted loads are required along with a sufficient medium-high volume prescription of the exercise (e.g. 8-10 repetitions x 2 sets x 2-5kg held) or, effectively challenging your positioning.
How can I make this easier? In terms of this specific exercise, reducing the amount of length you have on the muscles or lowering the repetitions is suffice. In order to reduce the length, a slight hinge or bend at the pelvis will reduce the pressure on the hamstring. Performing exercises such as a single or double leg romanian deadlift or hamstring sliders will allow muscular development as well as muscular awareness when progressing to the nordic hamstring curl.
How can I relate this to running and return to sport? Well, hamstring eccentric strength gains are inextricably linked to running improvements however, if you want a challenge specifically resisted running (e.g. sled pulling and pushing) and sprinting rather than longer running/jogging, increase eccentric length in the muscle!