I wonder this too. There is this study conducted on avians that connects stretching with hyperplasia.

"Progressive stretch overload of skeletal muscle results in hypertrophy before hyperplasia. Antonio J, Gonyea WJ

J Appl Physiol 1993; 75:1263-71.

Abstract

Intermittent stretch of the anterior latissimus dorsi (ALD) muscle produces fiber hypertrophy without fiber hyperplasia (J. Appl. Physiol. 74: 1893-1898, 1993).

This study was undertaken to determine if a progressive increase in load and duration of stretch would induce extremely large muscle fiber areas or if the fibers would reach a critical size before the onset of fiber hyperplasia. Weights ranging from 10 to 35% of the bird's mass were attached to the right wing of 26 adult quail while the left wing served as the intra-animal control. The stretch protocol was as follows: day 1 (10% wt), days 2 and 3 (rest), day 4 (15% wt), days 5-7 (rest), day 8 (20% wt), days 9 and 10 (rest), days 11-14 (25% wt), days 15 and 16 (rest), and days 17-38 (35% wt). Birds were killed after 12, 16, 20, 24, and 28 days of stretch not including rest days.

Muscle mass increased 174% (12 days), 196% (16 days), 225% (20 days), 264% (24 days), and 318% (28 days).

Muscle length increased 60% (12 days), 34% (16 days), 59% (20 days), 50% (24 days), and 51% (28 days). Mean fiber area increased 111% (12 days), 142% (16 days), 75% (20 days), 90% (24 days), and 39% (28 days).

Fiber number, which was measured histologically, increased significantly by 82% only in the 28 days of stretch group. The percentage of slow tonic fibers did not change for any of the time points examined.

Skeletal muscle fiber hyperplasia. Antonio J, Gonyea WJ

Med Sci Sports Exerc 1993; 25:1333-45.

Abstract Skeletal muscle enlargement in adult animals has been ascribed primarily to changes in fiber cross-sectional area (i.e., fiber hypertrophy); however, recent evidence from several laboratories suggests strongly that fiber hyperplasia contributes to muscle mass increases in adult animals and possibly human athletes.

Scientists have used three models to study the cellular mechanisms of muscle enlargement: compensatory hypertrophy, stretch, and exercise. Each of these models has provided direct as well as indirect evidence supporting the occurrence of muscle fiber hyperplasia.

Direct counts of muscle fibers using nitric acid digestion techniques have shown that both exercise and stretch overload result in significant increases (range = 9-52%) in fiber number. Indirect fiber counts using histological cross-sections have suggested fiber hyperplasia (range = 10-82%) in all three models.

Additionally, the expression of embryonic myosin isoforms have provided indirect evidence for new fiber formation in stretch overloaded muscle. Furthermore, satellite cells have been shown to be involved in muscle fiber hyperplasia in stretch and exercise."

Of course, anecdotal evidence that it decreases muscle growth:

I stretch my legs when I mbate, and my legs are very slender, but when I stop mbating for long periods of time, my legs seem to bulk up more. So it would seem stretches, at least the kind I am doing, kill my leg gains. But there are different kinds of stretches.