is lifting the only/best way to retain muscle?

This is a great unknown for me too. As well as getting my heart rate too high into the red zone (though very comfortable), will I burn muscle?

Thank you. Not certain why it's considered "The red zone". :-)

I've been reading a lot of stuff from Bret Contreras; he summarized a few studies here
http://www.fitnessrxwomen.com/training/workout-tips-advice/do-light-weights-tone-heavy-weights-bulk/

The body of literature overwhelmingly supports the notion that lighter weights can be used to build muscle mass, as long as effort is sufficient. In fact, sets carried out to momentary muscular failure using 30% of maximum strength for 24 reps per set has been shown to be more effective at synthesizing muscle than sets using 90% of maximum strength for 5 reps per set. 1

Taking this into account, Burd et al. 20122 noted that, “It is often recommended that heavier training intensities (∼70%–80% of maximal strength) be lifted to maximize muscle growth. However, we have reported that intensities as low as 30% of maximum strength, when lifted to volitional fatigue, are equally effective at stimulating muscle protein synthesis rates during resistance exercise recovery.” A limitation in their experiment is that it examined the transient effects of resistance exercise immediately following the training session. This information is certainly interesting, but ideally, you want long-term training studies to reference when exploring the effects of higher versus lower repetition ranges and muscle hypertrophy. Indeed, two recent training studies have emerged, both showing similar findings.

Longer Term Training Studies

Mitchell et al. 20123 had subjects perform ten weeks of the leg extension exercise. The subjects that performed high reps with 30% of their maximum strength saw similar gains in muscle growth compared to the subjects that performed medium reps with 80% of their maximum strength. This casted serious doubt on the claim that low reps are superior to high reps for muscle building. More recently, Schoenfeld et al. 20144 came to the same conclusion. Eight weeks of bodybuilding-style training involving 3 sets of 10 reps with 90 seconds in between sets was equally effective at building muscle as powerlifting-style training involving 7 sets of 3 reps with 3 minutes of rest in between sets. This research clearly calls into question the tenet that heavier weight is better than lighter weight for building muscle.

...

As long as effort is sufficiently high and training is carried out close to failure, similar results in terms of muscle growth will be seen whether training in low, medium, or high rep ranges. Therefore, training loads should be customized to the lifter according to their preferences. There is some data that indicates that using a combination of rep ranges in training would be optimal, since high reps appear to build type I muscle fibers to a greater degree than low rep training (but high rep and low rep training appear to be equal with regards to building type II muscle fibers),3 but this hypothesis warrants more investigation. In the meantime, train with the loads that you’re most comfortable with, and don’t buy into the notion that light weights are for toning and heavy weights are for bulking.

I think power training can retain or increase lbm (dependant on caloric deficit/surplus).

I'd put plyo stuff and sprinting in this category.

Advanced yoga is little different from advanced bodyweight stuff. So there's adequate scope for progressive resistance with it. Trig the volume and progress it sensibly then why shouldn't it work?

I know little about swimming, so can't really offer an opinion on it.

Just to throw this out there, but haven't there been studies on fish oil that show an increase in lbm even in people who are not training in any way. Could be wrong about that though... so there's a possibility of lbm increases without even cardio, let alone resistance. Obvs this would be a limited increase against a training response, but things are more complicated in the body than some people will admit...

jacksonpt wrote: »

Resistance training seems to be the key to muscle preservation.

So my follow up question is this - what exactly constitutes resistance training? Obviously lifting. Body weight work seems accepted as resistance training. Plyometrics? Yoga? Swimming? Hiking with a loaded pack?

Swimming has been a great resistance training for me, as well as some "lifting" type resistance with things like noodles and paddles in the water. Pulling my big self through water as well as working against the water has definitely strengthened my upper body and, to a lesser extent, the lower body.