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A new study landed in my feed last week, and I will admit the algorithm has my number. It steered me toward a question I have chewed on more than once here at FasterSkier: when it comes to low-intensity training, are you better off concentrating volume into one big week, or spreading the same volume evenly across several weeks? The easy move is to enjoy a paper that agrees with you and click away. I try not to do that. A study only earns its keep if I am willing to read the ones that argue against me with the same care I give the ones that pat me on the back. This one sits close to my own view, which is exactly why I want to handle it carefully.
What the researchers tested
Walther and colleagues, writing in the International Journal of Sports Physiology and Performance, set out to test whether concentrating low-intensity training into a high-volume block produces any adaptation that even distribution does not. They worked with 20 well-trained junior cross-country skiers in a crossover design, so every athlete completed both approaches and served as their own comparison. Total training volume was matched across the two protocols. Before and after each intervention, the researchers ran a battery of tests: VO2max, peak velocity at VO2max, lactate responses, submaximal economy markers, and subjective measures of recovery and fatigue.
The two protocols differed only in shape:
- BLOCK: one week at 160 percent of normal endurance volume, followed by three reduced-volume weeks.
- EVEN: the same total volume spread evenly across four weeks.
The point worth holding onto is that the totals were identical. Only the organization of the four weeks changed.
The performance results
Concentrating the volume into a block had no effect on performance. Both protocols nudged some variables in the right direction, and the improvements were statistically similar. VO2max, maximal aerobic speed, and lactate-threshold measures all moved to a comparable degree whether the work was stacked into a block or laid out evenly. That matters because block periodization is so often assumed to be the stronger option. Here, concentrating on a low-intensity load produced no extra adaptation beyond what consistent training already delivered.
The two approaches did not feel the same, though. During the high-volume week and the recovery week that followed, the BLOCK group reported lower mood, reduced feelings of recovery, and greater fatigue. The athletes tolerated the work, and there was no indication of increased injury or illness risk, though four weeks is a short window in which to base that claim. The concentrated approach simply costs more on the recovery side without being repaid in results. I would have liked to see heart rate variability tracked across both protocols. Autonomic data might have put real numbers to that recovery cost, rather than leaving it to a subjective report.
Why this matches what I have seen
This lines up with something I have watched play out across endurance sport for years. Adaptation comes from repeated exposure, not from the occasional enormous week that flattens recovery and chips away at the very adaptation you are chasing. A training model deserves to be judged on more than whether it works. Time to adaptation matters. So does recovery cost, psychological and autonomic strain, and whether an athlete can actually keep the thing going for months and years. The block protocol led to greater fatigue and poorer perceived recovery without a better outcome. From a coaching chair, that is not a small detail, and it weighs even heavier with junior athletes.
There is a fair counterargument, and it deserves room. Proponents of block periodization will point out that overload blocks build fatigue first and may reveal their benefits only over a longer horizon, and that a four-week window can miss those delayed adaptations. I see the logic, but I lean the other way. The longer the timeline an adaptation needs, the greater the room for overtraining and the thinner the signal you are actually working with. If a block needs four weeks to show its hand, there probably wasn’t much adaptive signal to begin with.
Why low intensity is the key qualifier
For low-intensity work, the physiological stress of any single session is modest by design. The adaptation seems to come from stacking many of those sessions on top of one another over time, not from cramming volume into a short window. When the totals match, the body appears to respond to how much training got done, not to how it was parceled out. That helps explain why athletes who lean on the occasional big week rarely pull ahead of the ones who just train, month after month, without drama. The big week feels harder. Harder is not the same as more adaptive.
The authors are careful not to overreach, and so am I. Their findings should not be stretched to cover every form of block periodization. The earlier work showing real benefits from block training generally concentrated high-intensity sessions, where the stimulus is far larger. This study looked only at low-intensity volume. Block periodization may well earn its place when the stimulus itself is potent. There is just little evidence that piling up low-intensity volume creates a stronger adaptive signal.
What it means for junior coaching
For junior endurance athletes, the practical read is straightforward. Do not expect a high-volume, low-intensity camp or an overload week to produce superior adaptations simply because the work is bunched together. Camps still earn their place for logistics, technique, and the team-building that holds a season together. They just do not appear to hand you a physiological edge once total volume is matched.
So here is where I land. Concentrating low-intensity volume into overload blocks does not seem to yield better short-term aerobic adaptation than spreading the same volume out, at least when the total volume is equal. I am not claiming block periodization does not work, or that all concentrated loading is a waste. What the evidence keeps pointing at, for aerobic base development, is that showing up consistently does more for an athlete than the occasional heroic training week. Over a season, the consistent skier and the big-week skier can bank the same hours. Only one of them pays the fatigue tax to get there.
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Jim Galanes
Coach, competitor, correspondent, commentator—Jim Galanes has spent a lifetime on cross country skis, always serving as a keen observer of our sport. A three-time Olympian in both Cross-Country and Nordic Combined, Jim has tested the theories, initiated the instruction, assessed the results. Now, FasterSkier is thrilled to announce that Jim joins our staff of writers and contributors, adding his unique and time-tested insights to the editorial offerings of this publication.
