Ejaculation involves a surprisingly large number of muscles working in a precise sequence. Some are smooth muscles deep inside the reproductive tract that you can’t consciously control, while others are skeletal muscles in the pelvic floor that contract rhythmically to propel semen outward. Understanding which muscles do what helps explain common ejaculatory problems and why pelvic floor training can make a difference.
Two Phases, Two Types of Muscle
Ejaculation isn’t a single event. It happens in two distinct phases, emission and expulsion, each powered by different muscle types under different nervous system control.
During emission, smooth muscle cells lining the reproductive tract contract in a coordinated sequence. This moves sperm from the storage ducts through the prostate and into the back of the urethra, mixing with fluid from the seminal vesicles and prostate along the way. You have no voluntary control over this phase. It’s driven by the sympathetic nervous system, the same branch responsible for your fight-or-flight response, originating from the lower thoracic and upper lumbar spine (roughly the T12 to L2 level).
Expulsion is the phase most people think of. Skeletal muscles in the pelvic floor contract rhythmically and forcefully to push semen out through the urethra. These contractions are involuntary during orgasm, but the muscles themselves can be voluntarily exercised at other times.
Smooth Muscles of the Emission Phase
The first muscles to activate are the smooth muscle walls of the vas deferens, the paired tubes that carry sperm from the testicles upward into the pelvis. Their coordinated contractions propel sperm toward the urethra. At the same time, smooth muscle in the walls of the seminal vesicles contracts to squeeze out the fructose-rich fluid that makes up the bulk of semen volume. The muscular capsule of the prostate also contracts, adding its own secretions to the mix.
These contractions happen sequentially, not all at once. The result is that sperm and seminal fluid arrive in the posterior urethra in the right order and at the right time, creating the sensation sometimes described as “ejaculatory inevitability,” the point of no return.
The Bladder Neck: A Critical Gatekeeper
As emission begins, smooth muscle fibers at the bladder neck tighten to seal off the bladder. This prevents semen from flowing backward into the bladder instead of forward through the penis. The closure is regulated by the sympathetic nervous system from the same T12 to L2 spinal segments that control emission.
When this mechanism fails, semen enters the bladder instead of exiting the body. This is called retrograde ejaculation. It’s not dangerous, but it produces a “dry” orgasm and is a common cause of infertility. Certain medications, diabetes-related nerve damage, and some prostate surgeries can impair bladder neck closure.
Bulbospongiosus: The Primary Expulsion Muscle
The bulbospongiosus (sometimes called the bulbocavernosus) is the single most important muscle for the expulsion phase. It wraps around the base of the penis and the bulb of the urethra. When it contracts rhythmically during orgasm, it compresses the urethra and forces semen outward in pulses. Research consistently identifies this muscle as primarily responsible for expelling semen.
These contractions are triggered involuntarily by the pudendal nerve, which originates from the S2 to S4 level of the sacral spinal cord. The pudendal nerve consolidates sensory information from the dorsal nerve of the penis and converts it into the rhythmic motor signals that drive expulsion.
Ischiocavernosus and Perineal Muscles
The ischiocavernosus muscles run along both sides of the base of the penis. Their primary job is generating penile rigidity by compressing the erectile chambers and producing pressures higher than normal blood pressure. During ejaculation, they contract alongside the bulbospongiosus, contributing to the force of expulsion.
Other perineal muscles in the pelvic floor also participate. The external urethral sphincter, which normally helps control urination, relaxes during expulsion to allow semen to pass through. Meanwhile, the surrounding striated muscles of the perineum contract in coordination to maintain pressure.
The Levator Ani: Deep Pelvic Floor Support
The levator ani is a broad sheet of muscle forming the floor of the pelvis. It plays supporting roles in urination, bowel movements, and sexual function. During ejaculation, contraction of the levator ani facilitates semen ejection by increasing pressure within the pelvic cavity. Think of it as the deeper muscular foundation that the more superficial muscles (bulbospongiosus, ischiocavernosus) work against.
Contraction Pattern During Orgasm
A typical orgasm from penile stimulation involves 4 to 8 pelvic muscle contractions. These happen rapidly and involuntarily. The first few contractions are the strongest and closest together, producing the initial forceful pulses of semen. Subsequent contractions become weaker and more spaced out. Interestingly, orgasms from prostatic stimulation have been associated with around 12 contractions, roughly double the typical number.
The entire expulsion sequence lasts only a few seconds. Every contraction is coordinated by the pudendal nerve, which fires in a rhythmic pattern that the brain does not consciously direct once the reflex has been initiated.
Pelvic Floor Training and Ejaculatory Function
Because the key expulsion muscles are skeletal muscles, they respond to exercise like any other muscle in your body. Pelvic floor exercises (commonly called Kegels) target the bulbospongiosus, ischiocavernosus, and levator ani. The basic movement involves contracting the muscles you’d use to stop urinating midstream, holding briefly, then releasing.
A randomized controlled trial published in the British Journal of General Practice found that men doing pelvic floor exercises were able to achieve stronger penile retraction and scrotal lift as their muscle strength improved. The study also found weak but positive evidence that orgasmic and ejaculatory function improved with training. Men starting these exercises often find the contractions difficult and slow at first, with responsiveness improving over weeks of consistent practice.
Stronger pelvic floor muscles can translate to more forceful ejaculatory contractions and better control over timing. This is why pelvic floor rehabilitation is sometimes recommended for men experiencing premature ejaculation or weak ejaculatory force, particularly after prostate procedures that may have affected the surrounding musculature.