One double-blind study published in the International Journal of Sports Nutrition and Exercise Metabolism tested whether or not deer antler velvet powder or extract had an impact on aerobic performance, endurance and “trainability of muscular strength” compared to a placebo. The subjects were adult males. They were given either a placebo, or deer antler extract or powder supplementation over a  10-week period while undergoing a strength-building routine. The men were measured for muscular strength, endurance, and VO2max before and after using deer antler. These results were determined by measuring circulating levels of testosterone, insulin-like growth factor, erythropoietin, red cell mass, plasma volume, and total blood volume.
First, the following disclaimer: Products that are sold as supplements (as opposed to medications) are not regulated by the Food and Drug Administration so they are not tested for safety, efficacy or standardization.  In other words, when you buy a supplement, there is no guarantee that what is in the bottle has been tested to see if it even contains the ingredient in question, let alone whether the ingredient actually does what it claims to.  (That’s not a value judgment, just the facts.)
Deer antler spray — a supplement commonly used in the fitness and sports industries that has a long history of use in Eastern medicine — is pretty much as strange as it sounds. Derived from the tissue found inside deer antlers, it’s reported to work by providing IGF-1 (insulin-like growth factor), a natural growth hormone found inside the human body that has potential to increase muscle mass and support recovery from injuries.
IGF-1 can help slow this aging process down by increasing the telomere length of our DNA. Telomeres are a protective "cap" at the end of each strand of our DNA which prevents the DNA from becoming damaged. DNA becomes damaged as the telomeres grow shorter with age. As more DNA strands become damaged, cells in our bodies can no longer function properly which results in many medical conditions, diseases, and even death. This is how IGF-1 can help longevity. It does this by promoting healthy DNA strands to keep our cellular functions optimal.
A systemic review on human interventions[25] makes note of a study conducted on patients of osteoarthritis (Edelman et al. 2000; cannot be located online) which found improvements in joint pain symptoms relative to baseline in the Velvet Antler group and not placebo, although a lack of information on blinding and randomization precludes results that can be drawn from this study.