Will BLS rescuers be fit enough for chest-compression only CPR?

So this is what I just read

Garza and his research colleagues analyzed the effect of new resuscitation protocols implemented in 2006 by the Kansas City Emergency Medical Services. Under the changes, the highest priority became chest compressions, and rescuers were told to perform 50 chest compressions before pausing to administer two breaths to the patient. Current American Heart Association guidelines for CPR call for 30 compressions followed by two breaths.
After the changes, overall survival for out-of-hospital cardiac arrest patients increased from 7.5 percent to 13.9 percent. The findings appear in the May 4 online issue of Circulation.

Reference: Focusing on CPR Improves Survival - Medline Plus

So it was 30:2, maybe it will be recommended in the near future a 50:2 approach. There are more and more sustainers of and published evidence that chest-compression only CPR could be more effective.

I am worried about the rescuers' fitness in the future: will they be physically prepared to deal with all those compressions? Especially if you start as shown in the picture (via flickr) I am sure you will be exhausted after less than 1 minute of compressions.