Progressive load training: an extra 15 minutes a day resulted in 301 fewer injuries in the NFL.

Progressive overload training is not a theoretical principle, but a specific protocol. An analysis of NFL practices in the April 2026 American Journal of Sports Medicine found that teams which added only 15 minutes of training per day during the first week of training camp had significantly fewer muscle strains. This is the top league in the world, not amateurs. This is applicable for amateur fitness returns too.

What did the study authors do

The Herzog team and colleagues from Duke University gained access to the training logs of 32 NFL teams over 5 seasons. The standardised metric was training volume in minutes of work per day during pre-season training camps. The first week is critical, when players return from their off-season break and ramp up their workload.

Group the teams according to how they built up their workload: some started straight away with the standard seasonal workload of 100%, others added 10–15 minutes a day, and others fell somewhere in between.

Injury outcome - muscle strains (hamstring, quadriceps, calf, groin). This is the most common type of injury in team sports, taking players out of the game for 2-6 weeks.

Progressive overload training in the NFL has shown it can lead to significant improvements in player strength, power, and endurance. It helps athletes adapt to increasing demands, reducing the risk of injury while enhancing performance.

Teams using progressive load training — that is, gradually adding 15 minutes a day — experienced 30–40% fewer muscle strains in the first four weeks of the season. This is not a marginal effect; it is a significant difference.

This is particularly evident in hamstring strains, which most often occur following a sudden increase in speed work. The hamstrings adapt to high eccentric loads more slowly than the core or the shoulder girdle. When a player, after a six-week break, attempts a 100-metre sprint, it is a recipe for injury.

Teams that adopted a “gradual approach” did not reduce the intensity – peak intensity remained the same. They increased the duration of sessions gradually. On the first day, sessions were 60–75% of the standard duration. The second day — +15 mins. The third — another +15. By the end of the week — full seasonal volume.

Why isn’t this the “10% rule”?”

The classic rule for amateur runners is: “Don’t increase your weekly mileage by more than 10%.” It has been around in running literature since the 1980s and actually lacks a strong evidence base. A 2008 study by Buist involving 532 runners showed that increases of 10% and 24% resulted in roughly the same injury rates.

What works more reliably is progressive load training over a short period. Not “+10% per week”, but “+10–20% per session or day”, with careful monitoring of how you feel. NFL data confirms exactly this: the first 5–7 days are critical, as that’s when a mistake costs the most.

The logic is simple. The first day after a break, your body is in “forgetfulness mode”. Tendons are out of sync with muscles, neuromuscular coordination is impaired, and cardiovascular capacity is reduced. All of this doesn't recover instantly but over 7-14 days. If you go at full load on the first day, your muscles might be ready, but your tendons and control networks won't be. This is the moment of injury.

How to transfer progressive overload training to an amateur level

Scenario 1 — Getting back into shape after illness or a long break. Don’t try to do the same as you did six months ago from your very first session. For the first 3–5 sessions, aim for 60–70% of your usual volume using the same exercises. The intensity should be slightly lower, with fewer repetitions and longer rest periods between sets.

Scenario 2 — new type of load. Switched from running to strength training, or vice versa. The first week involves 50–60 reps, which seems like a “reasonable” volume. The body reacts to the new stimulus differently than it did to the old one. A runner’s Achilles tendons aren’t ready for deep weighted squats, even if the muscles are.

Scenario 3 — Return to sport after injury. There's separate literature for this – a physiotherapist should have specific return-to-play phases. Progressive load training here isn't “an extra 15 minutes a day”, but rather structured phases 4-6 with progression criteria.

Scenario 4 - Starting from scratch at 40+. Particular caution. In experiments on humans aged 50-65, the risk of hamstring injuries is three times higher than in younger individuals. Strength training after 50 should go even slower — the first 2-3 weeks use bodyweight without additional resistance.

Markers that you're growing too fast

Body signals you need to read:

• DOMS (delayed onset muscle soreness) lasts longer than 72 hours after exercise
• For the next session, the feeling of “heavy legs” from the first set, not the fifth.
• Reduced performance despite the same weight (not managing the same reps as last week)
• Elevated resting heart rate of 5-10 beats in the morning
• Bad sleep, irritability

One of these indicators is worth paying attention to. If two or three appear together, this is a signal to reduce the volume by 30–50% for the next session and take an extra day off. The principle is the same as when working with a variety of training Listening to your body is more important than sticking to a plan on paper.

What remains unanswered

The study is observational. Teams that had a gradual build-up might have had better physios, a better recovery culture, and better communication between coaches and medical staff. It is difficult to separate the “effect of the build-up itself” from the “effect of quality organisation”.

The NFL are professionals with ideal infrastructure. An amateur without a coach, with their own schedule, with irregular sleep and nutrition – they have a higher risk of injury anyway, regardless of how they increase their volume.

However, the direction of the effect is consistent with 30 years of cumulative literature on load and injury. This is not a new finding, but rather a confirmation of the principle at the highest level of sport.

What about cross-session recovery?

Progressive overload training isn't about “slowly increasing”. Adequate recovery is needed between sessions – otherwise, even gradual progression leads to overtraining.

Basic markers for sufficient recovery: morning heart rate is not increased by 5+ beats, sleep is good quality, the first 5 minutes of the warm-up of the next workout feel easy without excessive leg heaviness. If even one marker is off, a rest day is more important than the next session.

This is particularly relevant for people aged 40 and over, whose total recovery time is 30–50% longer than that of 20-year-olds for the same volume of exercise.

Conclusion: progressive load training is not about reducing, but about stretching

Progressive overload training isn't a complex theory, not “macrocycle periodisation”. It's a simple rule: when you're getting back into shape, the first week is for adaptation, not your maximum. Adding 15 minutes a day results in drastically fewer injuries without losing the final effect.

The shortest way to lose a month is to try to make up a week in one day.

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Sources

• Herzog MM, Shiue KY, Lee RY, et al. Gradual training adaptation during preseason camps reduces muscle strain injuries in the National Football League. Am J Sports Med. 2026. DOI: 10.1177/03635465261430924
• Buist I et al. The GRONORUN study: is a graded training program for novice runners effective in preventing running related injuries? BMC Musculoskelet Disord. 2008;9:24. DOI: 10.1186/1471-2474-9-24