How much strength do you lose during contest prep?

Short answer

Less than you'd think. In a study that followed 19 people for about 21 weeks, strength was broadly maintained, and in a 1-person case that did lose strength, the big three lifts fell 7-10%. Dieting blocked muscle gain but not strength gain.

How much strength do you lose during contest prep?
'Lose weight → lose muscle → lose your lifts' — does this formula hold?
People say months of near-starvation before a show wipe out the weights you can lift. We checked studies that actually measured strength in people preparing for contests to see how much it really drops.
A study that followed 19 people
Strength held over about 21 weeks of prep
19 people lost 7.1 kg over about 21 weeks before a show: 5.8 kg of fat and 1.7 kg of lean mass (muscle and everything except fat). Yet a test of pulling a bar as hard as possible from thigh height showed strength was broadly maintained.
Pooling case studies told the same story
Most that measured strength saw it hold or rise
An analysis of 11 contest-prep case studies (15 people) found most studies that measured strength saw it held or increased. In 1 person who lost 11.7 kg over 14 weeks, lean mass fell 5.0 kg, yet front-thigh strength relative to body weight rose 9-16%.
Why does strength hold when muscle drops?
Dieting only blocked muscle gain
An analysis of trials where people lifted for 3+ weeks while eating less found muscle gain was smaller than with enough food, but strength gain showed no difference. A shortfall of about 500 kcal a day stopped muscle gain. Strength is not set by muscle size alone.
Even the drops stayed within 10%
A 200 kg squat became 180 kg over 18 weeks
1 person prepped for 18 weeks, going from 81.8 kg to 77.8 kg. The squat fell from 200 kg to 180 kg, bench press from 135 kg to 125 kg, and deadlift from 240 kg to 220 kg, a 7-10% drop. Relative to body weight, the drop was 2.6-5.4%.
The big drops came from extreme leanness
One person lost up to 19% of lower-body force
1 person who dropped body fat from 14.8% to 4.5% lost strength, and it had not fully returned 6 months after the show. Another who went from 20.3% to 12.2% body fat lost up to 19% of peak lower-body force and was still 5-8% down 8 months later.
Bottom line: strength drops less than you'd think
Across groups it held; drops mostly stayed within 10%
In the 19-person study strength was broadly maintained, and in the 1-person case that lost strength, the 3 big lifts fell 7-10%. The largest drop, 19%, came from a case of extreme leanness. Lean mass came back 2.7 kg within 6 weeks after the show, so read most prep strength loss as temporary.