Stimulus to Fatigue Ratio (SFR) in CrossFit
Three Types of Stimulus
1. Strength
Mechanisms:
Recruit more motor units
Inhibit GTO
Hypertrophy
Outcomes:
Can handle larger loads without encountering the muscles inability to supply the necessary force
All movements in that pattern require a lower % of 1RM
Contractions become more repeatable
Examples:
Top sets, accessory work
2. Conditioning
Mechanisms:
Increase rate of metabolite clearance
Increase metabolite tolerance (if high intensity)
Increase relative contribution of oxidative metabolism
Increase sustainable power outputs (lactate threshold and critical power)
Outcomes:
Can handle higher work rates without encountering the muscles’ maximum metabolite tolerance
Contractions become more repeatable
Examples:
Intervals, metcons, zone 2
3. Skill
Mechanisms:
Stretch-strengthening, greater range of motion around joints, less tension in the muscle required to accomplish the work, more work with less metabolites
Fewer, lower tension unnecessary contractions, lower RPE
Outcomes:
Contractions become more repeatable
Examples:
Warmups, tempo work, non-fatigued gymnastics, light-moderate weightlifting
2 Types of Fatigue
1. Central Fatigue
Perturbations in neurochemistry cause a decrease in the voluntary activation of muscles; directly related to a decrease in the frequency and synchronization of motoneurons and a reduced drive from the motor cortex; in short, having to do with the central nervous system (CNS)
Examples:
Axial loading (set of heavy deads and then you don’t want to do anything else)
Sleep deprivation
2. Peripheral Fatigue
Decrease in the contractile strength of muscle fibers with changes in the mechanisms underlying the transmission of muscle action potentials; e.g. the depletion of muscle glycogen or the accumulation of certain metabolites in the muscle fibers (H+, ADP, Pi); in short, having to do with the working muscles
Examples:
Soft tissue damage – sore knees, sore shoulders – pain causes restraint in training
Depletion of fuel substrates (mainly muscle glycogen)
Every program produces a certain amount of stimuli in exchange for a certain amount of fatigue.
In general, bigger stimulus = bigger fatigue
Therefore, the game is not to eliminate fatigue. But to approach fatigue to the maximum the athlete can recover from.
The best program maximizes the stimuli that will produce the biggest gain in CrossFit performance while approaching fatigue to the maximum that the athlete can recover from.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8997532/
https://pubmed.ncbi.nlm.nih.gov/32647476/
Stimulus to Fatigue Ratio (SFR) in CrossFit
Three Types of Stimulus
1. Strength
Mechanisms:
Recruit more motor units
Inhibit GTO
Hypertrophy
Outcomes:
Can handle larger loads without encountering the muscles inability to supply the necessary force
All movements in that pattern require a lower % of 1RM
Contractions become more repeatable
Examples:
Top sets, accessory work
2. Conditioning
Mechanisms:
Increase rate of metabolite clearance
Increase metabolite tolerance (if high intensity)
Increase relative contribution of oxidative metabolism
Increase sustainable power outputs (lactate threshold and critical power)
Outcomes:
Can handle higher work rates without encountering the muscles’ maximum metabolite tolerance
Contractions become more repeatable
Examples:
Intervals, metcons, zone 2
3. Skill
Mechanisms:
Stretch-strengthening, greater range of motion around joints, less tension in the muscle required to accomplish the work, more work with less metabolites
Fewer, lower tension unnecessary contractions, lower RPE
Outcomes:
Contractions become more repeatable
Examples:
Warmups, tempo work, non-fatigued gymnastics, light-moderate weightlifting
2 Types of Fatigue
1. Central Fatigue
Perturbations in neurochemistry cause a decrease in the voluntary activation of muscles; directly related to a decrease in the frequency and synchronization of motoneurons and a reduced drive from the motor cortex; in short, having to do with the central nervous system (CNS)
Examples:
Axial loading (set of heavy deads and then you don’t want to do anything else)
Sleep deprivation
2. Peripheral Fatigue
Decrease in the contractile strength of muscle fibers with changes in the mechanisms underlying the transmission of muscle action potentials; e.g. the depletion of muscle glycogen or the accumulation of certain metabolites in the muscle fibers (H+, ADP, Pi); in short, having to do with the working muscles
Examples:
Soft tissue damage – sore knees, sore shoulders – pain causes restraint in training
Depletion of fuel substrates (mainly muscle glycogen)
Every program produces a certain amount of stimuli in exchange for a certain amount of fatigue.
In general, bigger stimulus = bigger fatigue
Therefore, the game is not to eliminate fatigue. But to approach fatigue to the maximum the athlete can recover from.
The best program maximizes the stimuli that will produce the biggest gain in CrossFit performance while approaching fatigue to the maximum that the athlete can recover from.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8997532/
https://pubmed.ncbi.nlm.nih.gov/32647476/