Answer: FTP increases and applying different forms of training stress require small planned decreases in TSS to maximize training benefits.
Reduce TSS Between Training Phases to Get Faster
Within a progressively structured training plan, each new week sees a slight increase in the overall amount of stress (TSS), while each workout sees a similar bump in the amount of work demanded, typically via more or longer intervals. These weekly increases are all part of what call a structured round of “loading”.
After a few weeks of this loading pattern, a week of reduced training, or “deloading”, is scheduled to allow the body to absorb the accumulated stress and positively adapt to it. This temporary drop in TSS is intended to yield faster riders with higher work capacities. These riders must then reassess their new level of fitness before embarking on another round of loading.
Increased FTP is Why The First Week of Subsequent Loading Phases Sees a Slight Decline in TSS
FTP is simply a measure of your work capacity. This means a higher FTP translates to a higher capability for performing work. When you increase your FTP through training, an escalation in training load occurs because every workout from that point forward will require higher power output, yield more energy/work, and inflict greater stress on the body in a number of ways.
The first 1-2 weeks following an FTP increase usually allow an athlete to adjust to his or her new power levels without the added stress of an increased TSS load. As the body adjusts to these new demands, the weekly TSS will resume its usual rate of increase (ramp rate) and the training response is likely to be more favorable due to this brief, but necessary training stress reduction.
The Effects of an Increased FTP on Your Training
When athletes increase their FTP they effectively increase their capacity to perform work, i.e. they can do more. But doing more involves more muscle mass, requires more fuel for the muscles, necessitates stricter recovery regimens, and exacts a heftier physiologic toll on other systems of the body.
To drive this point home, consider a rider with an FTP of 200 watts could generate roughly 3700 kilojoules/kJ of energy (work) during a 450-TSS week while an athlete with an FTP of 300 watts could generate something closer to 4900 kJ for the very same 450 TSS. Higher FTP = higher work capacity.
Now consider an athlete with an FTP of 200 watts who completes the first 5 weeks of Sweet Spot Base I, recovers for a week and then resumes training with Sweet Spot Base II. As a result of properly progressed training loads and close adherence to each week’s structured training, his FTP has risen to 220 watts. This new, higher level of work capacity could be dangerous, or at best unproductive, if it were coupled with yet another increase in weekly TSS.
Not All Training Stress is Created Equal
When following the Base/Build/Specialty cycle, workouts retain a certain level of homogeneity within each training phase — they’re all pretty similar from week to week within that phase of training. But when moving from one training phase to another, the variety and type of workouts can change rather dramatically. As a result, comparing weekly TSS becomes problematic because not all TSS are created equally.
For example, the physical toll exacted by 130 TSS accumulated via 2.75 hours ridden steadily between 65-75% FTP (Town Hill) is substantially different than the stress inflicted by 130 TSS derived from 30 minutes of 15-second microbursts at 150% FTP (Spanish Needle +2). Same TSS, different fitness adaptations, different bodily stress.
This change in the stress inflicted by different types of workouts is most apparent when shifting from a more homogenous, escalating-TSS Build phase into a widely varied, steady-TSS Specialty training plan. But to simply increase TSS without any concern for the impact the added TSS might have or the composition of the workouts themselves is shortsighted and commonly overwhelms riders’ recovery capabilities and consequently, comes at the expense of performance gains.
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Main Takeway
While a TSS decline, temporary or fixed, may at first seem to fly in the face of performance improvement, each of these transitions is purposeful and based on time-tested physiological principles.
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