A Gym Session the Day Before the Race? What "Priming" Research Shows

Athletes in sprinting, jumping and team sports often do a short gym session on the morning of competition or the day before. The idea, usually called "priming", has spread through social media and into endurance sport, with some runners and triathletes now doing heavy squats or jumps the day before a race to feel sharper.

This article covers what priming is, what the research shows and who it was done in. The honest picture is that the evidence comes almost entirely from power and team-sport athletes, a few small endurance trials haven't found a benefit, and nothing has tested it before a long-course triathlon. That gap is what this article is about.

What priming is

Priming is a low-volume strength or power session done within about 48 hours of competition. A 2019 review by Harrison and colleagues in Sports Medicine described two kinds of stimulus that have been studied:

• Heavy resistance exercise, at 85% or more of one-repetition maximum.
• Ballistic exercise at lower loads, such as jump squats or throws.

It's different from post-activation potentiation, where a heavy lift a few minutes before an effort temporarily enhances it. Potentiation lasts minutes. Priming is meant to have effects hours or days later. The review found improvements in various neuromuscular measures at times between 1 and 48 hours after priming, in both upper- and lower-body tests. But it described the evidence as limited, and said its application to specific sports and its broader effects were unclear.

How common is it?

In 2020, Harrison and colleagues published a survey in the Journal of Science and Medicine in Sport of 69 practitioners who prescribe resistance training for high-performance athletes.

• 51% prescribed priming exercise.
• 59% of those scheduled it within 8 hours of competition.
• Sessions were short: about 3 sets of about 4 repetitions, usually with two or three upper-body and two lower-body exercises.
• The most common exercises were unloaded jumps, loaded jumps and bench press.
• Loads ranged from bodyweight to 85% of one-repetition maximum or more.

The authors concluded that many practitioners use priming, with a wide range of methods, despite limited supporting evidence.

The studies in power and team-sport athletes

Morning lifting before an afternoon test

A 2014 study by Cook and colleagues in the Journal of Science and Medicine in Sport involved 18 semi-professional rugby union players. On separate days, in random order, they either rested, did 5 × 40 m sprints, or did a 3-repetition maximum bench press and squat in the morning. About six hours later, they were tested.

• After the morning weights session, afternoon countermovement jump power, 40 m sprint time, and 3-repetition maximum bench press and squat were all better than after rest or sprints.
• Morning sprints improved afternoon 40 m time compared with rest.
• Salivary testosterone, which normally falls from morning to afternoon, didn't fall after the weights session.

The authors couldn't say whether testosterone caused the improvement or simply accompanied it.

A session the day before

A 2018 study by Tsoukos and colleagues in the Journal of Strength and Conditioning Research involved 17 well-trained male power and team-sport athletes aged around 23.

• The priming session: 5 sets of 4 jump squats at 40% of one-repetition maximum, with 3 minutes' rest between sets.
• The control: rest.
• Testing: before, and 24 and 48 hours later.

The results:

• Countermovement jump height improved by 5.1% at 24 hours and 3.0% at 48 hours.
• Reactive strength improved by 10.7% at 24 hours only.
• Rate of force development improved at 24 hours, with a smaller effect at 48 hours.

The authors suggested that a low-volume power session one day before competition could help. It's one of the clearest results in the field, but it's in young, strong male athletes, and the outcomes were jumps and force, not endurance.

Mixed results overall

A 2023 review by Holmberg and colleagues in the Strength and Conditioning Journal looked at what changes the response to priming. It found some studies showed improvements, others found no change, and some found performance got worse. The authors attributed the inconsistency mainly to the many different variables across studies, such as load, volume, timing and the athletes' characteristics.

The endurance studies

Cross-country skiers

The most rigorous endurance study is a 2021 trial by Rud and colleagues in the International Journal of Sports Physiology and Performance. It involved 8 male national-level cross-country skiers with an average VO2max of 69 mL/kg/min.

• The priming session: 3 sets of 3 repetitions at about 85% to 90% of one-repetition maximum in squats and sitting pullovers, 5 hours before testing.
• The tests: a double-poling test to exhaustion lasting about 3 minutes, 30 m double-poling sprints, oxygen cost at submaximal speed and jumps.

The results, compared with no priming:

• Time to exhaustion was 3.6% longer, but this wasn't statistically significant.
• Sprints, jumps and oxygen cost showed no meaningful differences.
• Electrical stimulation tests showed low-frequency fatigue, a sign of muscle fatigue, only after priming. It was 12% lower than before.

The authors concluded the session didn't improve short double-poling performance and may have been too strenuous. This was a 3-minute effort. Inference: if a heavy session left measurable fatigue 5 hours later in highly trained skiers, it's unlikely to help a race lasting several hours.

Runners and the 800 m

A 2023 master's thesis by Antti Ihamäki at the University of Jyväskylä in Finland tested a priming session the afternoon before an 800 m run. It involved 11 runners (3 women, 8 men) with at least two years of endurance training.

• The priming session: leg press, isometric calf presses, repeated countermovement jumps and drop jumps, at about 4 to 6 pm.
• The test: an 800 m run the next morning, on average about 16 hours later, compared with a non-priming session.

The results:

• 800 m time and pacing didn't change.
• Jump performance didn't improve.
• Runners with more muscle soreness after the session tended to benefit less.

This is an unpublished thesis rather than a peer-reviewed study, and it's small. But it's one of very few tests in runners, and it found no benefit.

Why endurance races are different

Priming was developed for sports that depend on peak power: sprinting, jumping, throwing and the collisions and accelerations of team sports. A long-course triathlon depends on things priming doesn't target:

• Aerobic capacity and threshold, which don't change in a day.
• Efficiency on the bike and run.
• Fuelling and pacing over many hours.
• Fatigue resistance late in the race, covered in TriForward's "Why Watts Fade".

A priming session also has costs. A 2017 review by Doma, Deakin and Bentley in Sports Medicine concluded that a single resistance session can impair endurance performance for several hours to several days if recovery is inadequate, through altered muscle recruitment, lower efficiency, soreness and lower muscle glycogen. Inference: for a race that depends on efficiency and fatigue resistance over many hours, the potential cost of a pre-race gym session is easier to see than the potential benefit.

Nothing tests long-course triathlon

To be plain: no study has tested resistance priming before a long-course triathlon, an Ironman, a half-distance race or even an Olympic-distance triathlon. The closest evidence is a 3-minute ski test and an 800 m run, and neither found a benefit.

That leaves three possible positions:

• It might help a little with the swim start, a hard first few minutes on the bike or the feeling of being "sharp". This is plausible but untested.
• It might make no difference, which is what the endurance studies found.
• It might hurt, if the session causes soreness or fatigue. The skier study found signs of muscle fatigue 5 hours later.

Why priming feels convincing

Part of priming's appeal is how it feels. Many athletes say that after a short, heavy session they feel springier and more alert the next day, and the jump results in the Tsoukos study suggest that for power athletes this feeling can be real. But feeling sharp and racing faster aren't the same thing. In the Rud study, perceived readiness didn't differ significantly between priming and no priming, and performance didn't improve. In the 800 m thesis, runners who were sorer after the session tended to benefit less.

There's also a selection problem in what you see online. Athletes who prime and then race well tend to share it. Athletes who prime and feel flat rarely do. Inference: a sprinter's or footballer's routine on social media tells you what they believe works for them, not what works for a triathlete.

Sprint and Olympic-distance racing

Shorter triathlons are closer to the events where priming has been studied, although still much longer. A sprint triathlon lasts around an hour or more for most age-groupers, and an Olympic-distance race two to three hours. Both have hard starts, and draft-legal races involve surges and sprints. Inference: if priming were to help a triathlete anywhere, short, draft-legal racing is the most plausible place. But even the 800 m, which lasts around two minutes, showed no benefit in the one study that tested it, so the case remains untested rather than promising.

Older athletes

Masters triathletes face an extra consideration. TriForward's "The Masters Training Week" covers studies suggesting older athletes may recover more slowly from muscle-damaging exercise and feel less recovered after hard sessions. Inference: a session that leaves a 23-year-old rugby player feeling sharp the next day could leave a 55-year-old triathlete feeling heavy. None of the priming studies here included older athletes.

How this fits with tapering

TriForward's "Tapering for an Ironman" found that tapers work best when they cut volume while keeping intensity and training frequency. Many triathletes who lift continue with short, lighter sessions during the taper. That's different from priming: it maintains strength without adding a new stimulus. Inference: a short, familiar session early in race week fits within normal taper practice. A new or heavy session the day before the race is a different thing, and that's the one the evidence doesn't support.

If you want to experiment

The following is inference, not a tested protocol:

1. Don't try it for the first time before a key race. Test it before a hard training session or a minor race.
2. Keep it familiar. Use exercises and loads you already do, at a lower volume, such as a couple of sets of a few repetitions.
3. Avoid eccentric-heavy and new work. Deep squats, Romanian deadlifts, drop jumps and lunges are the most likely to cause soreness.
4. Judge it by how the race feels, not by how jumpy you feel the next morning.
5. If in doubt, leave it out. For a long-course race, the downside risk is larger than the likely benefit.

A triathlon scenario

The following example is illustrative, not drawn from a study. A 38-year-old triathlete sees a video of a sprinter squatting the day before a race and plans to do heavy squats and box jumps the afternoon before her 70.3. She normally lifts twice a week but hasn't done jumps for months.

Based on the evidence above, she might:

• Skip the box jumps. They're unfamiliar and could cause soreness during the race.
• Do her usual short lifting session early in race week, at lower volume, if she wants to keep the routine.
• Try a short priming session before a hard training ride in the off-season, to see how she responds.

Common mistakes

• Copying sprint and team-sport routines for a race lasting several hours.
• Adding new exercises in race week.
• Going heavy and high-volume, which the skier study suggests may cause fatigue.
• Assuming feeling "sharp" means racing faster.
• Trying it for the first time on race day.

What we don't know

• Whether priming has any effect on triathlon performance at any distance.
• Effects in women, who are largely absent from the research.
• Effects in age-group and older athletes, since most studies involve young, strong athletes.
• The best load, volume and timing for endurance athletes, if there is one.
• Whether lighter, ballistic priming, such as a few jumps rather than heavy lifting, avoids the fatigue seen in the skier study. The Tsoukos study used light jump squats, but in power athletes, not endurance athletes.
• How priming interacts with travel, race-week nerves and fuelling, which matter far more in long-course racing.

References

• Harrison PW, James LP, McGuigan MR, Jenkins DG, Kelly VG. Resistance priming to enhance neuromuscular performance in sport: evidence, potential mechanisms and directions for future research. Sports Medicine, 2019;49(10):1499–1514. doi:10.1007/s40279-019-01136-3
• Harrison PW, James LP, McGuigan MR, Jenkins DG, Kelly VG. Prevalence and application of priming exercise in high performance sport. Journal of Science and Medicine in Sport, 2020;23(3):297–303. doi:10.1016/j.jsams.2019.09.010
• Holmberg P, Harrison P, Jenkins D, Kelly V. Factors modulating the priming response to resistance and stretch-shortening cycle exercise stimuli. Strength and Conditioning Journal, 2023;45(2):188–206. doi:10.1519/SSC.0000000000000728
• Cook C, Kilduff L, Crewther B, Beaven M, West D. Morning based strength training improves afternoon physical performance in rugby union players. Journal of Science and Medicine in Sport, 2014;17(3):317–321. doi:10.1016/j.jsams.2013.04.016
• Tsoukos A, Veligekas P, Brown LE, Terzis G, Bogdanis GC. Delayed effects of a low-volume, power-type resistance exercise session on explosive performance. Journal of Strength and Conditioning Research, 2018;32(3):643–650. doi:10.1519/JSC.0000000000001812
• Rud B, Øygard E, Dahl EB, Paulsen G, Losnegard T. The effect of resistance exercise priming in the morning on afternoon sprint cross-country skiing performance. International Journal of Sports Physiology and Performance, 2021;16(12):1786–1793. doi:10.1123/ijspp.2020-0881
• Ihamäki A. Valmistavan voimaharjoituksen vaikutukset 800 metrin juoksun suorituskykyyn [Effects of priming strength exercise on 800 m running performance]. Master's thesis, University of Jyväskylä, 2023. urn:nbn:fi:jyu-202306153838
• Doma K, Deakin GB, Bentley DJ. Implications of impaired endurance performance following single bouts of resistance training: an alternate concurrent training perspective. Sports Medicine, 2017;47(11):2187–2200. doi:10.1007/s40279-017-0758-3