How long does strength training last?

Study [1]:  The authors took 20 healthy men with at least a year of resistance training and were between the ages of 18-30 and randomly allocated them into two groups: one group receiving whey protein and another receiving a placebo.  They both participated in resistance training.  The researchers were looking to find a.) if 2 weeks of detraining results in strength loss and b.) if a is true then does whey protein possibly prevent strength loss.

10 subjects: 4 weeks of training, 2 week break period, and 4 weeks of training + placebo
10 subjects: 4 weeks of training, 2 week break period, and 4 weeks of training + 25 grams of whey

Resistance training: 2 days of upper body and 2 days of lower body sessions per week (4 total), using 3 sets of 10 reps at 75% of their 1RM and 2 minutes of rest in between sets.

Results: 

Non-significant results for the following:
Lean Mass
Fat Mass
Cross Sectional area of the quad

Significant results:
Leg press strength at various time points including after 2 weeks of detraining

Conclusion:  2 weeks of detraining did not cause significant muscle (lean mass) or strength loss and is undifferentiated by whey protein consumption.

My thoughts:  It is a little concerning that both groups failed to show significant results in lean mass, fat mass, or cross sectional area.  The authors hypothesized that the subjects were not consuming enough calories to sufficiently accrue lean mass.  There was a nonsignificant trend towards more lean mass in the protein group, but these results were not significant due possibly to the small study size.  In the end, the fact that 2 weeks of detraining does not lead to significant loss of mass or strength is significant.  Now you can take a week or two off from the gym and not have to worry about losing potential gains, which is perfect for periods of recuperation and of course, vacation!

1.  Hwang, P. S., Andre, T. L., McKinley-Barnard, S. K., Morales Marroquín, F. E., Gann, J. J., Song, J. J., & Willoughby, D. S. (2017). Resistance Training–Induced Elevations in Muscular Strength in Trained Men Are Maintained After 2 Weeks of Detraining and Not Differentially Affected by Whey Protein Supplementation. Journal of Strength and Conditioning Research, 31(4), 869-881. doi:10.1519/jsc.0000000000001807