You have to look at all of this with a grain of salt -
"French researchers found that the addition of two weight-training sessions per week for 14 weeks significantly increased maximal strength and running economy while maintaining peak power in triathletes."
So their maximal strength and running economy increased. That's great, but are they faster?
"Meanwhile, the control group – which only did endurance training – gained no maximal strength or running economy, and their peak power actually decreased (who do you think would win that all-out sprint at the finish line?)."
Again, it's too bad their peak power decreased. But this is meaningless if we're not talking about running speed. And to answer your question about the all-out sprint, it's usually the guy who is in better shape aerobically who wins. The "stronger" guy has to use his anaerobic reserves just to keep up and then doesn't have them at the end.
"And, interestingly, the combined endurance with resistance training group saw greater increases in VO2max over the course of the intervention (2)."
For the third time, simply measuring these variables on their own is meaningless. There is no gold medal for VO2max.
"Scientists at the Research Institute for Olympic Sports at the University of Jyvaskyla in Finland found that replacing 32% of regular endurance training volume with explosive resistance training for nine weeks improved 5km times, running economy, VO2max, maximal 20m speed, and performance on a 5-jump test. With the exception of VO2max, none of these measures improved in the control group that just did endurance training (3)."
OK, FINALLY we are measuring 5km times. All that other garbage is meaningless. I guarantee I could beat someone like Ritz in a 20 m sprint or 5-jump test but that doesn't matter in a distance race, does it?
My question is why there was no improvement in 5km times for the control group that did only endurance training. Nine weeks is a long time. I actually just started my season last week and my peak race for the fall is in 8 weeks. I expect to be about 45 seconds faster over 5km at the end of those 8 weeks (if past history is any measure).
If the endurance training given to the control group was so ineffective that it produced zero improvements in 5km time over 9 weeks, then I could see how cutting that regimen by 32% wouldn't really harm anything either. Then adding strength training - yeah, it will help.
A better study would have been one in which the endurance training for the control group was EFFECTIVE and lead to 5km improvements. Then let's see what happening when you cut 32% of an effective plan and substitute it with something else. That could be interesting.
"University of Illinois researchers found that addition of three resistance training sessions for ten weeks improved short-term endurance performance by 11% and 13% during cycling and running, respectively. Additionally, the researchers noted that “long-term cycling to exhaustion at 80% VO2max increased from 71 to 85 min after the addition of strength training"
This makes sense. If you add strength training it can only help. My beef is with running less in order to make room for this.
"The take-home message is that running is more than just VO2max, anaerobic threshold, and a good pair of sneakers; it’s also about localized muscular endurance and nervous system efficiency. And, you can’t have strength endurance unless you’ve got strength. Build a solid foundation and you’ll be a complete runner."
I will agree with this statement, but again, I don't think you've shown that SUBSTITUTING strength training in place of running is better.