Well I hate to break it to the folks here, but it looks like it's not the weight that you lift but the fact that you get muscular fatigue that's the critical point in building muscle. I guess horse stance may make your legs stronger after all.

"We conclude that a high intensity-low volume training bout is inferior to a low intensity-high volume bout in stimulating an anabolic response. Quantity of work, however, is important even at low intensities. Our data support the notion that a lower intensity-higher volume resistance exercise paradigm may ultimately be more effective in stimulating hypertrophy [increase in muscle size]."

"The perspective provided in this review highlights that other resistance protocols, beyond the often discussed high-intensity training, can be effective in stimulating a muscle building response that may translate into bigger muscles after resistance training," says lead author Nicholas Burd. "These findings have important implications from a public health standpoint because skeletal muscle mass is a large contributor to daily energy expenditure and it assists in weight management. Additionally, skeletal muscle mass, because of its overall size, is the primary site of blood sugar disposal and thus will likely play a role in reducing the risk for development of type II diabetes."

The authors from McMaster University conducted a series of experiments that manipulated various resistance exercise variables (e.g., intensity, volume, and muscle time under tension). They found that high-intensity muscle contractions derived from lifting heavy loads were not the only drivers of exercise-induced muscle development. In resistance-trained young men a lower workout intensity and a higher volume of repetitions of resistance exercise, performed until failure, was equally effective in stimulating muscle proteins as a heavy workout intensity at lower repetition rates. An additional benefit of the low-intensity workout is that the higher repetitions required to achieve fatigue will also be beneficial for sustaining the muscle building response for days.

Journal Reference:

Nicholas A. Burd, Cameron J. Mitchell, Tyler A. Churchward-Venne, Stuart M. Phillips. Bigger weights may not beget bigger muscles: evidence from acute muscle protein synthetic responses after resistance exercise. Applied Physiology, Nutrition, and Metabolism, 2012 DOI: 10.1139/h2012-022