To answer this question, we're going to look at a study published in 2011.

The aim of this study was to compare changes in :

• body composition
• Strength
• power 

During either:

• Fast weight loss (1% of body weight per week)
• Slower weight loss (0.7% of body weight per week)

All athletes included 4 resistance-training sessions/wk in their usual training regimen

The average amount of weight lost was 4.2kg for both groups.  The fast weight loss group did it in 5.3 weeks, the slower group took 8.5 weeks.

Let's looks at some specific results now.
Changes in lean body mass:

• Slower group: gained 2.1% of lean body mass
• Fast group: lost 0.2% of lean body mass

This suggests that the fast group may have lost muscle mass

Change in fat mass:

• Slower group: lost 21% of their fat mass
• Fast group: lost 31% of their fat mass

Changes in performance:

• 40m sprint
  • Fast group: no change
  • Slow group: no change
• Counter movement jump
  • Fast group: no change
  • Slow group: increased 7%
• 1RM  press
  • Fast group: 6.4%  increase
  • Slow group: 13.6%  increase
• 1RM pull
  • Fast group: 4% increase
  • Slow group: 10.3% increase
• 1RM squat
  • Fast group: 8.9% increase
  • Slow group: 11.9% increase

While both groups lost the same amount of body weight, their body composition changes were significantly different.  This study suggests that slower rates of body weight reduction are better for preserving/gaining muscle mass as well as losing more body fat.  
In terms of performance, we saw an increase in performance for both groups for most of the tests, as we should.  These are elite athletes that are continuing to train, so improvements are expected.  However,  the percent increase in performance across all measures was significantly higher in the slower weight loss group.  

This suggests that quick weight loss does not allow for as much athletic improvement as does slower weight loss.  If your goal is to continue to improve while in a caloric deficit, you are much better off losing weight at a slower rate.  

I will argue that I still think 0.7% of body weight loss per week is still a bit aggressive for most athletes, particularly strength athletes.  In my experience, I start seeing a decline in performance for most people above 0.6% loss per week, and for some strength athletes, even that is too aggressive and we have to go with a more conservative 0.4% of body weight lost per week.  

What have your experiences been with weight loss as an athlete?  Have you seen a decrease in strength and performance? 

At FFN we specialize in managing weight cuts for athletes to preserve their strength (and usually gain strength during the process).  If you want expert help with your next weight cut, you can work with us here!