The goal off the bike would be to train as specific as possible in the weight room with exercises which employ that whole triple extension (hip/knee/ankle) as witnessed on the bike, which the OP's exercise has. Specificity can only take you so far (riding the bike), then it would be time for greater strength stimulation (weight room), although specificity (riding) will always remain king. Case in point, my power output on my road bike kept increasing the stronger I got with the deadlift & hip thrust. This is seen with track cyclists, very strong guys that can put out huge levels of power. The OP would benefit more from his exercise than doing tricep extensions etc.
Which exercise(s) would allow you to use more weight:
a) The OPs exercise
b) The powersnatch and bent over row
If you come to the same conclusion as me, namely that b) allows more weight, which exercises do you think will benefit the development of muscular strength and power more? The answer is b) as well, because exercises that allow more weight, will also allow more progress over a longer period of time. Making the transfer of that strength to the bike is going to be accomplished with doing stuff on the bike (specificity), but the physical prerequisites in terms of muscle strength are best developed in the weight room with solid exercises that allow a lot of weight to be moved over a great range of motion and with the use of the most muscle mass possible.
x2
"The goal off the bike would be to train as specific as possible in the weight room with exercises which employ that whole triple extension (hip/knee/ankle) as witnessed on the bike, which the OP's exercise has." -- sickenin vendetta
It's never about training as specific as possible in the weight room. There's a degree of specificity that needs to occur, but, as you increase the level of specificity, you decrease the ability to cause gains in maximal strength. Maximal strength is the umbrella which makes all things possible. That exercise can only get you so far. Let's just imagine that it was effective & specific, thus allowing for significant transfer to mountain biking (which I doubt). That exercise would only be good to improve explosive strength SLIGHTLY, specific to mountain biking. There's just not enough room for progressive overload, time under tension, or appropriate loading of the actual muscle groups/movements of the human body. Heavy squatting alone would raise someone's ability to generate more force in a variety of movements specific to mountain biking. Power snatch is a much more sane version of loading the muscle groups & movements specific to mountain biking, it allows for more progress via addition of load than the OP's exercise. The problem with power snatch alone is that it would fail for the same reasons that the OP's exercise would fail, time under tension & the ability to increase load without progressing max strength will result in far less ability to make long term gains, but this is far more of a problem in the OP's exercise than with power snatching/power cleaning/oly power variants.
Take for example people who train using loaded jumps & completely neglect max strength training. They might achieve a few inches of gains, but long term, they will hardly achieve anything significant. They will stagnate forever unless proper max strength training is incorporated.
If you want to improve triple extension, you have to improve max strength in the various movements that make up the triple extension: knee extension, hip extension, and plantar flexion. That can be done via:
- isolation (calve raises, glute bridges/hypers, knee extensions)
- multi joint (squat, oly variants)
- special exercises (bounds/depth jumps, oly variants + other power variants)
- specificity (doing movements specific to your sport/event, ie mountain biking, jumping, sprinting etc)
etc
Specificity is a topic that is completely understood for the most part imo.. For example, the specificity between a half squat & deep squat is significant, one allows you to overload the most important prime movers for jumping significantly whilst the other does not. However, the difference between IMPROVEMENTS in max/explosive strength potential between half squatting and loaded jumps, is HUGE. Half squatting improvement causes considerable adaptations to the human organism, while loaded jumps does not. Stress is very important. The more specific you get, generally, the amount stress decreases. For example,
- loaded jumps (very specific) vs half squat (less specific)
- riding a bike in an easy gear @ max effort vs riding a bike in a very hard gear @ max effort
The only caveat to all of that, is shocklike exercises, such as depth jumps and downhill sprinting. Those are extremely specific yet extremely intensive, but that's a whole different monster because you're using "shock" to target protective mechanisms of the CNS, you can't do that with snatches, OP's exercise, loaded jumps, etc.
peace