One will gain muscle but do not expect anything extreme as it is not going to pack on size.
Even when looking at some thing such as recombinant human growth hormone (rhGH) in low doses it will not result in significant muscle gains and even when used in higher doses significant muscle gain is only seen when rhGH is combined with high doses of testosterone as there is a synergistic effect.
As far as MK-77 how much of the muscle gain is related to increased intra-cellular water stores as oppose to increased actin/myosin.
As we know muscle cell is roughly 70% water and as much as intra-cellular water stores contribute to increased size of the overall muscle what we are truly after is increases in new proteins (actin/myosin).
Here is a RCT in older men:
https://www.smr.jsexmed.org/article/S2050-0521(17)30032-X/fulltext
Effects of an Oral Ghrelin Mimetic on Body Composition and Clinical Outcomes in Healthy Older Adults: A Randomized, Controlled Trial
Healthy elderly individuals who took the ghrelin mimetic MK-677 experienced a sustained increase in the amplitude of pulsatile GH secretion and IGF-I to levels seen in young adults. The likely mechanism was activation of the ghrelin receptor by MK-677, with feedback by IGF-I preventing excess GH production. MK-677 increased fat-free mass (FFM) by 1.6 kg relative to placebo. To provide perspective, an adult's average lifetime loss of FFM is ~ 5.5 kg (
3).
The concomitant increase in intracellular water, which reflects body cell mass (25), is the likely mechanism for the increase in FFM.
Ghrelin stimulates GH secretion, but it also has effects that are not attributable to increased GH. In this study, a ghrelin mimetic transiently increased appetite, a novel effect that might counteract physiological anorexia, which is one cause of weight loss in the elderly (
26,
27), Ghrelin increases fat stores, unlike GH which is lipolytic. We found that body weight increased more after MK-677 than placebo. Although total fat mass increased in both groups, limb fat and limb lean mass increased more with MK-677 than placebo. Surprisingly, thigh muscle cross-sectional area did not increase, although the study is not powered to detect small but potentially important differences with the imprecise single slice CT method that we used. GH reduces abdominal visceral fat (AVF) in GH-deficient adults (
28) and abdominally obese, postmenopausal women (
29), but not normal elderly subjects (
30). Despite increasing GH levels, MK-677 did not affect AVF, perhaps because its combined orexigenic and adipogenic effects counteracted the lipolytic effects of enhanced GH. Finally, although MK-677 did not reduce AVF, it did reduce LDL levels at 12 months, an effect not seen with GH in normal elderly subjects (
8).