Multimodal Rehabilitation Shows Striking Gains in Hard Flaccid Syndrome Case Series

Hard flaccid syndrome (HFS) is an emerging and poorly understood male sexual dysfunction in which the penis remains persistently semi-rigid even in the flaccid state. Men with the condition often report altered penile sensation, erectile dysfunction, ejaculatory problems, and pelvic or perineal pain, yet standardized diagnostic criteria and population-level prevalence estimates remain unavailable. Many patients discover the term HFS through internet forums rather than from a clinician, and single-modality treatments such as nerve blocks, muscle relaxants, or pain medications have generally shown limited success. A new retrospective case series published in Frontiers in Rehabilitation Sciences now reports that a comprehensive multimodal rehabilitation protocol was associated with substantial improvements in erection hardness, penile satisfaction, sexual interest, and overall physical and mental health in 32 men with HFS.

The study, conducted by Christopher L. Mendias and Tariq M. Awan of the Performance Medicine Institute in Phoenix, Arizona, is described by the authors as the largest treatment-focused report on HFS to date. The 32 participants had a median age of 28.9 years, a median body mass index of 27.7 kilograms per square meter, and a median symptom duration of 18 months, with durations ranging from 4 to 60 months. To be eligible, patients had to report a persistent or recurrent semi-rigid quality of the flaccid penis on most days for at least three months, accompanied by at least one additional feature such as altered penile sensation, erectile dysfunction, ejaculatory dysfunction, or perineal or pelvic pain. Patients were excluded when symptoms could be better explained by acute penile trauma, active genitourinary infection, Peyronie’s disease, neurologic disease, or uncontrolled endocrine, cardiovascular, or psychiatric conditions.

The treatment protocol was anchored in neurophysiology, biomechanics, exercise physiology, connective tissue mechanobiology, and behavioral therapy. Each session combined seven synergistic modalities: class IV laser therapy, radial pressure wave shockwave therapy, therapeutic ultrasound, superficial dry needling, manual therapy, biofeedback training, and progressive therapeutic exercise. Patients also took daily oral tadalafil at a dose of 5 milligrams to support nitric oxide and cyclic GMP-mediated smooth muscle relaxation and vascular function. Sessions occurred once or twice per week, with a median of nine sessions per patient, and anatomic targets and dosing were individualized according to symptoms, examination findings, and tolerance. Patients were generally encouraged to continue treatment until they reached a satisfied or very satisfied state with overall penile function.

Each modality was chosen for specific biological rationale. Class IV laser therapy, delivered to the penile shaft at approximately 700 to 800 joules split between 810 and 980 nanometer wavelengths, was intended as photobiomodulation to support nitric oxide-mediated microvascular signaling. Radial pressure wave shockwave therapy was applied to the dorsal and lateral aspects of the penis at 4 to 6 hertz, delivering 1,000 to 2,000 pulses per session, because its divergent superficial field distributes mechanical stimulation across a broader region of myofascial tightness than focused shockwaves. Therapeutic ultrasound at 3 megahertz and 1.0 to 1.2 watts per square centimeter was used to improve blood flow and reduce fascial tightness, an approach adapted from Peyronie’s disease research. Superficial dry needling targeted the penile fascia without penetrating the dartos fascia, and was also applied over the lower abdomen, hip, and low back in symptomatic patients.

The behavioral and exercise components were equally structured. Patients received education on penile anatomy, erection physiology, pain neurophysiology, and psychosocial factors, with the goals of reducing fear and maladaptive beliefs and improving adherence. Those reporting high-frequency, prolonged, or high-force masturbation received counseling with individualized step-down plans over four to eight weeks, and patients with problematic pornography use received education on sexual cue reactivity and self-directed reduction strategies. Biofeedback training emphasized pelvic floor relaxation or downtraining using a noninvasive device, and manual therapy included myofascial release and instrument-assisted soft tissue mobilization. Therapeutic exercise progressed through three stages over two to six weeks each, from relaxation and low-load control through stabilization to integrated strength, with additional exercises for comorbid hip or low back pathology.

The results were striking. Median scores on the Erection Hardness Scale, an ordinal measure from 0 to 4, increased from 2 at baseline to 4 at treatment end, a transition from erections generally insufficient for penetration to fully rigid erections in most patients. At baseline, only 8 of 32 patients, or 25 percent, achieved an erection hardness score of 3 or higher; by treatment end, all 32 patients did, with 72 percent reaching the maximum score of 4. Overall, 91 percent of patients improved by at least one category, none worsened, and the changes were statistically significant at P less than 0.01. Median penile function satisfaction rose from 2, indicating dissatisfaction, to 5, indicating very high satisfaction, with all 32 patients improving by at least one category.

Patient-reported quality-of-life measures also improved significantly. PROMIS Interest in Sexual Activity scores rose from a median of 38.4 to 54.8, a change that exceeded the 2 to 6 T-score range commonly cited as clinically meaningful. PROMIS Global Health physical and mental component summary scores increased from 50.8 to 54.1 and from 50.8 to 53.3 respectively, both within the clinically meaningful range. The clinical presentation of the cohort was notably heterogeneous: low back pain affected 53 percent of patients, hip or groin pain 38 percent, pelvic floor pain or tightness 31 percent, and urinary symptoms 28 percent, alongside morning erection alterations in 59 percent, ejaculatory dysfunction in 56 percent, and erectile dysfunction in 50 percent. Relationship or dating stress related to symptoms was reported by 72 percent of patients.

To explain these findings, the authors propose a hypothesis-generating mechanistic framework. Penile flaccidity is maintained through tonic alpha-1 adrenergic and RhoA/Rho kinase-mediated contraction of cavernosal smooth muscle driven by sympathetic fibers from spinal segments T11 to L2, while parasympathetic nitric oxide and cyclic GMP signaling from S2 to S4 promotes relaxation and blood filling. The dartos fascia contains myofibroblasts and smooth muscle under sympathetic control, and the tunica albuginea provides the passive mechanical constraint enabling the veno-occlusive mechanism. The authors hypothesize that increased sympathetic outflow, potentially driven by nociceptive input from low back, hip, or pelvic pathology, could sustain semi-rigidity through alpha-1 and RhoA/ROCK signaling in both cavernosal tissue and dartos fascia. Notably, the genitofemoral, ilioinguinal, and iliohypogastric nerves arise from the same spinal levels as sympathetic outflow to the hypogastric plexus, providing an anatomical route through which peripheral musculoskeletal pathology could influence penile tone.

Each treatment component maps onto this framework. Preclinical studies suggest dry needling can induce cytoskeletal remodeling and myofibroblast relaxation, release adenosine that inhibits nociceptive transmission, and promote local nitric oxide production. Shockwave therapy has been shown to reduce myofibroblast tension and may decrease alpha-1 adrenergic receptor expression, while photobiomodulation may modify RhoA/ROCK activity through cyclic GMP signaling. Thermal ultrasound can activate nitric oxide signaling and inhibit ROCK activation, and tadalafil sustains cyclic GMP levels by inhibiting phosphodiesterase type 5, deactivating the calcium-sensitization pathway that maintains tonic smooth muscle contraction. The authors also frame repetitive mechanical loading from aggressive masturbation, reported by 41 percent of patients, as a potential overuse injury sustained by reward-circuit sensitization that blunts the nociceptive feedback normally limiting continued loading of injured tissue.

The authors are careful to emphasize the limitations of the study. Because care was delivered in routine clinical practice without a control group, and because all patients received multiple interventions including daily tadalafil, the design cannot determine the efficacy of any specific component or of the protocol as a whole. The retrospective single-center design, the absence of long-term follow-up, the lack of validated HFS-specific outcome instruments, and the vulnerability of self-reported outcomes to expectation effects all constrain interpretation. Prior treatments in the cohort had mixed results, and one patient experienced worsening after self-injecting the unapproved peptide BPC-157 into his penis outside medical guidance, a caution the authors highlight given the absence of meaningful human subjects data for such compounds. Nevertheless, the consistency and magnitude of the within-patient changes, the universal improvement in satisfaction, and the convergence of musculoskeletal, autonomic, and behavioral features support the authors’ refined model of HFS as a multidimensional condition in which heterogeneous entry points converge on shared neurovascular, sensory, musculoskeletal, and behavioral maintenance pathways. The findings, they conclude, provide a rationale for prospective controlled trials that formally test each component, develop validated HFS-specific outcome measures, and evaluate the durability of these encouraging results.

Subject of Research: Multimodal rehabilitation outcomes in men with hard flaccid syndrome

Article Title: Multimodal rehabilitation for hard flaccid syndrome in a retrospective case series

Article References: Mendias, C. L., & Awan, T. M. (2026). Multimodal rehabilitation for hard flaccid syndrome in a retrospective case series. Frontiers in Rehabilitation Sciences, 7, Article 1970062. https://doi.org/10.3389/fresc.2026.1970062

Image Credits: AI Generated

DOI: 10.3389/fresc.2026.1970062

Keywords: hard flaccid syndrome, erectile dysfunction, pelvic floor rehabilitation, shockwave therapy, photobiomodulation, dry needling, tadalafil, PROMIS, chronic pelvic pain, male sexual dysfunction, biofeedback, therapeutic exercise