








































CLINICAL OUTCOMES RESEARCH 

 

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All rights reserved. ISSN Online 2577-8188                                                                        Volume 2 – Issue 1 – February 2019 
 

A Novel Approach to Treating Acute Hamstring Functional 
Neuromuscular Disorder-Effects of Primal Reflex Release Technique 
Lucas Bianco, DAT, LAT, ATC1; James May, DAT, LAT, ATC2; Alan Nasypany, EdD, LAT, ATC2 

1BIOKINETIX, Chicago, IL; 2University of Idaho, Moscow, ID 
 

 
ABSTRACT 

Hamstring injuries have an occurrence rate of 3.05 per 1000 
athlete exposures in intercollegiate athletics. Current clinical 
practice recommendations for rehabilitation of hamstring 
injuries are based on pathoanatomical muscle tissue healing 
timeframes. The purpose of this study was to examine the 
effects of modulating the nervous system with Primal Reflex 
Release Technique (PRRT) in patients clinically diagnosed with 
functional neuromuscular hamstring muscle-related disorder 
(FNHD). In this a priori case series, PRRT was utilized in four 
patients participating in intercollegiate, National Collegiate 
Athletic Association Division II, athletics to evaluate Numeric 
Pain Rating Scale (NRS) for current pain, Disablement of the 
Physically Active (DPA) scale, modified Patient Specific 
Functional Scale (PSFS), and Active Knee Extension Test 
(AKET). The initial pre-treatment to post-treatment average 
difference for NRS (3.25±2.5 points) and AKET (11±2.16°) 
improved by an amount that satisfied MCID and MCD 
respectively. The pre-treatment to one-week follow-up 
average difference for NRS (5.5±2.3 points), PSFS 
(4.75±2.5 points), and AKET (20.5±14°) improved by an 
amount that satisfied MCID or MCD. The average timeline for 
discharge to full unrestricted activity was 2.75 days. In the 
four patients classified with a functional neuromuscular muscle 
disorder (FNMD), PRRT was utilized as the only manual 
therapy intervention. Through modulation of the nervous 
system, the outcomes reported by the patients were both 
meaningful and clinically significant. Based on the results and 
the current standard of care for similar patients, the need for 
further research into this paradigm is warranted. Hamstring 
injuries continue to be a significant clinical injury in the athletic 
patient population. A thorough evaluation and appropriate 
classification of muscle injury can help clinicians decided an 
effective treatment for the patient. Clinicians seeking to 
improve patient outcomes may benefit from considering a 
paradigm that modifies the neural allostatic loads. 
 
Key Phrases 
Autonomic nervous system, patient-reported outcomes, 
clinician-rated outcomes 
 
Correspondence 
Dr. Lucas Bianco, 3205 Street Lynchburg, VA 24501. 
E-mail: lucasbianco4915@gmail.com  
 
Full Citation 
Bianco L. A Novel Approach to Treating Acute Hamstring 
Functional Neuromuscular Disorder-Effects of Primal Reflex 
Release Technique. Clin Pract Athl Train. 2019;2(1):19-31. 
https://doi.org/10.31622/2019/0001.5.  
 
Submitted: December 9, 2018 Accepted: February 26, 2018 
 

INTRODUCTION 

Hamstring injuries are a common pathology 

within physically active patient populations.1-6 
Injury to the hamstring muscle complex can 
present as tissue damage leading to pain and 
functional limitations.1-4,5-8 Structural damage, 
ranging from micro-trauma to macro-trauma, can 
occur when the force placed on the hamstring 
muscle is greater than the mechanical limits of the 
tissue.9,10 Functional limitations, not structural 
damage, are frequently used to classify a 
patient with a hamstring injury, and determine 
treatment parameters based on 
recommendations of tissue healing timeframes.6-

8,11 It is possible that a portion of these injuries 
have minimal or no structural damage and are 
FNMDs, thus they do not need to adhere to the 
recommended tissue healing timeframes.  

Hamstring injuries are prevalent in the 
intercollegiate athletic population, with a rate of 
3.05 per 1000 athlete exposure.12 The goals of 
hamstring rehabilitation include decreasing pain, 
restoring function, and returning to the prior level 
of sports performance with minimal risk of 
reinjury.1,2,7,11 Previous research on hamstring 
treatment and return to play programs has been 
completed for patients classified with hamstring 
injury. However, the re-injury rates for this clinical 
significant injury have been consistent over the 
past 20 years.1,2,4,8,11-13 With an increased risk 
of re-injury rate in intercollegiate athletics,  
further research is required to determine more 
effective interventions and treatment theories to 
decrease pain, restore range of motion (ROM), 
and improve function following classification of a 
hamstring injury.  



A Novel Approach to Treating Acute Hamstring Functional Neuromuscular  
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The pathoanatomical evaluation is recommended 
as the means for assessing a patient with a 
possible hamstring injury.1,2,7,8,10,14 The widely 
used, O’Donoghue Muscle Injury Classification 
system correlates tissue damage to loss of 
function.15 Based on this classification system, 
patients who present with pain and decreased 
function would be classified with a grade I or II 
hamstring strain. A recent consensus statement on 
muscle injuries in sport provides a new 
comprehensive classification system.16 The Munich 
Muscle Injury Classification system (Figure 1) was 
used by the treating clinician (TC) to sub-classify 

these patients. Based on this new classification 
system, patients treated in this case series would 
be classified as having a FNMD. The neural 
component of a musculoskeletal injury can easily 
be overlooked as it is not commonly associated 
or treated under the tissue model.17 As 
rehabilitation theories evolve to meet the 
progressive neurophysiologic research, clinicians 
may desire interventions purposed to create 
ideal function of the neurological system, rather 
than protocols encompassing the myopic muscle 
tissue healing model. 

 
 

 
 
 
Figure 1. Munich Muscle Classification16  

Patients with hamstring injuries in this study were classified with a Type 2A Muscle-related Neuromuscular 
Muscle Disorder and treated with PRRT, an innovative neurophysiological approach to treatment Patients 
with hamstring injuries in this study were classified with a Type 2B Muscle-related Neuromuscular Muscle 
Disorder and treated with PRRT, an innovative neurophysiological approach to treatment. 

A. Indirect 
Muscle Injury/ 

Disorder

Functional 
Muscle 

Disorder

Type 1: 
Overexertion-
related Muscle 

Disorder

Type 1A: Fatigue-induced Muscle 
Disorder

Type 1B: Delayed-onset Muscle 
Soreness 

Type 2: 
Neuromuscular 
Muscle Disorder

Type 2A: Spine-related 
Neuromuscular Muscle Disorder

Type 2B:  Muscle-related 
Neuromuscular Muscle Disorder

Strucual 
Muscle 
Injury

Type 3: 
Partial Muscle 

Tear 

Type 3A: Minor Partial Muscle 
Tear

Type 3B: Moderate Partial 
Muscle Tear

Type 4: 
(Sub)total 

Tear

Subtotal Complete 
Muscle Tear

Tendinous 
Avulsion

B. Direct 
Muscle Injury

Contusion

Laceration



A Novel Approach to Treating Acute Hamstring Functional Neuromuscular  
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All rights reserved. ISSN Online 2577-8188                                                                        Volume 2 – Issue 1 – February 2019 
 

The central nervous system (CNS) and peripheral 
nervous system (PNS) are directly related, and 
function in unison to provide appropriate sensory 
information to the brain to maintain a state of 
allostasis throughout the body.18-20 Allostatic 
modulations in loading of the muscle tissue are 
often due to facilitated neurons and/or inhibited 
neurons creating abnormal function.20 
Neurophysiologist, Sir Charles Sherrington, 
introduced the law of reciprocal innervation 
which is used in therapeutic techniques, such as 
proprioceptive neuromuscular facilitation, to 
relax the agonist muscle via reflexive stimulation 
of the antagonist muscle.21 The use of reciprocal 
innervation may be an effective treatment when 
the nervous system is in need of a modulating 
external stimulus.22 Expanding on this theory, 
withdrawal and startle reflexes that lead to 
muscle spasm and possibly pain can be due to 
mal-adaptation or abnormal stimulation of the 
nervous system.19 As a result of trauma (e.g., high 
speed running or agility movements), the nervous 
system may remain “up-regulated” and unable 
to restore a state of more ideal allostasis. In this 
up-regulated state, the use of an external 
stimulus to reset the CNS can resolve pain and 
restore function instantly.19,23 The creator of 
PRRT, John Iams, recognized that reflex 
responses to startling and/or painful events may 
persist in the form of facilitated or inhibited 
muscles, which leads to compensatory patterns, 
pain, dysfunction.23 Through modulating the CNS 
through the PNS, PRRT, an innovative treatment 
paradigm, can help reset the nervous system to a 
more ideal allostatic load following a traumatic 
incident such as a mechanism of injury leading to 
a hamstring injury. The use of PRRT in clinical 

practice has been demonstrated in the 
literature.24-26 The purpose of this study was to 
examine the effects of modulating the nervous 
system with PRRT in patients classified with 
functional neuromuscular hamstring muscle-
related disorder (FNHD). 

PATIENTS 

Four patients (3 males and 1 female) averaging 
(19.75±1.5 years of age) actively participating 
in intercollegiate athletics (Table 1) reported to 
the athletic training clinic with posterior thigh 
pain. All four patients were evaluated by a 
certified athletic trainer and met criteria to be 
included in this study. Each patient was classified 
with FNMD and treated by the same athletic 
trainer with four years of clinical practice 
experience who had completed, The Primal 
Reflex Release Technique™ Home Study Course, 
and The Primal Reflex Release Technique™ Live-
Training Seminar. Based on the a priori design, 
the patients were not treated with any other 
therapeutic interventions. Patient-oriented 
evidence (POE) and clinician-oriented evidence 
(COE) outcome measures were collected for each 
patient over the course of treatment. The 
Numeric Pain Rating Scale (NRS) for current pain, 
Disablement of the Physically Active (DPA) scale, 
and modified Patient Specific Functional Scale 
(PSFS) were all included as POE. The COE 
classified measure was the, Active Knee 
Extension Test (AKET), and hamstring manual 
muscle test (MMT). The Institutional Review Board 
(IRB) of the two universities involved in this study 
approved the collection and dissemination of 
outcomes. All participants provided written 

Table 1. Demographics and Evaluation Information 

Patient Age Gender Sport Location of Pain in 
Posterior Thigh Involved Side 

1 18 Female Cross Country Lateral Distal Third Right 
2 19 Male Soccer Middle Third Left 

3 21 Male Basketball Lateral Middle 
Third Left 

4 21 Male Basketball Medial Proximal 
Third Left 



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consent to have their non-identifiable information 
included in this study. 

At the time of initial evaluation, each patient 
reported pain with a decrease in active ROM 
and function in the affected extremity compared 
bilaterally. Due to the short time period from 
onset of injury to evaluation of the patient (within 
1-2 days), lack of structural damage diagnosis, 
and Munich muscle injury classification each 
patient was determined to have sustained a 
neuromuscular muscle disorder. One patient self-
reported a previous “hamstring strain” on his 
contralateral side, while the other patients 
reported no previous hamstring pathology. 
Following the evaluation, POE and COE 
measures were completed. Patients were 
included if they had the following outcome 
scores; NRS of ≥2/10, AKET measurement of 
≤70˚ on involved side, and a PSFS score of 
≤8/10 (Table 2). 

INTERVENTION 

The initial PRRT treatment session was completed 
immediately following the initial evaluation and 
collection of baseline patient outcome measures. 
The patient was positioned supine on a treatment 
table for all treatments. Then the TC provided a 
tactile stimulus the patient’s muscle bellies and 
tendons, or a quick movement the patient’s limb 
to create a reflexive response. The stimulus 
activates proprioceptors in the local tissue 
through reciprocal innervation that can lead to a 
more ideal allostatic load in the nervous 
system.21-23 Starting with the involved side, each 
technique was completed for approximately 12 
seconds, followed by the intervention on the 
contralateral limb. Four PRRT treatment 
techniques in the same sequence were utilized on 
each patient.  

The intervention consisted of the following 
sequence: Hamstring Down-Regulate (dR) (Figure 
2), Gastrocnemius Reset (Figure 3), Medial 
Knee/ Sacroiliac (SI) Joint Reset (Figure 4), and 

SI Bilateral Release (Figure 5), and was 
completed bilaterally, for a total of 2-3 minutes 
per session. After completion of the treatment, 
the patient stood up and then walked the length 
of the clinic two times, a total of approximately 
60 feet. Then AKET and PSFS were reassessed, 
along with the NRS, at the conclusion of the initial 
treatment session.   

OUTCOME MEASURES 

The NRS, PSFS, MMT, and AKET were assessed 
at the following time-points: pre- and post-initial 
treatment session, discharge, one-week, and six-
week follow-up assessment. The DPAS was 
collected at the pre-initial treatment session, one-
week, and six-week follow-up assessment. 
Following the evaluation and collection of initial 
outcome measures, each patient received the 
PRRT sequence described below. Total number of 
treatments and days to discharge were tracked 
for each patient. 

Numeric Rating Scale & Disablement of the 
Physically Active 

The NRS and DPAS patient-reported outcomes 
assessments measured each patient’s perception 
of pain and disablement. The NRS is an 11-point 
pain scale where 0 is “no pain” and 10 is “the 
worst pain imaginable.” Scores reported for the 
NRS represent patient reported current pain in a 
weight bearing position (i.e. standing) at the time 
of assessment. A change of 2 points or greater is 
considered a Minimal Clinically Important 
Difference (MCID) for the NRS.27 The DPAS was 
designed and validated for assessing 
disablement in physically active individuals. A 
64-point scale with 16 possible identifiers of 
disablement individually scored on a 5-point 
Likert scale where zero is “no issues” and 4 is a 
“severe” issue. For acute conditions, a MCID is 
reached with a 9-point difference in scores.28 

 



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All rights reserved. ISSN Online 2577-8188                                                                        Volume 2 – Issue 1 – February 2019  

Figure 2. Hamstring down-regulate (dR).22-23 
Patient rests foot on the TC’s shoulder while 
stimulation is applied to the patella tendon and 
each hamstring (semitendinosus, 
semimembranosus, and biceps femoris) muscle 
bellies. 

 

Figure 4. Medial knee/Sacroiliac (SI) joint 
Reset.23 Stimulation is provided to the adductor 
magnus muscle superior to the knee  and pes 
anserine inferior to the knee. 

 

Figure 3. Gastrocnemius Reset.23 Patient 
maintains hip and knee flexion and ankle 
dorsiflexion while the TC applies stimulation to 
the patella tendon and ankle dorsiflexors (tibialis 
anterior, and extensor digitorum longus). 

 

Figure 5. SI Bilateral Release.22 The TC provided 
an external rotation stimulus into external hip 
rotation which the patient reacted against 
activating his/her internal hip rotators. 

  

Table 2. Inclusion and Exclusion Criteria 
Inclusion Exclusion 

Acute, sudden posterior thigh pain NRS of ≥2/10 
MOI: acceleration or deceleration during running 
Tender area to palpate on hamstring 
Weakness compared bilaterally with knee flexion <5/5 MMT 
Asymmetrical range of motion >5˚ 
Involved side AKET measurement of <70˚ 
Modified PSFS ≤8/10  

Gross deformity 
Visible ecchymosis 
Previous hamstring strain 
within 6 months 
No specific MOI 

 



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Range of Motion (ROM) 

To objectively assess ROM, the AKET was 
completed. The AKET is completed with the 
patient lying supine. First, the Clinometer phone 
application (plaincodeTM, Stephanskirchen, 
Germany) was utilized to position the angle of 
hip flexion at 90° by placing the device on the 
posterior aspect of the thigh. Once in 90° of hip 
flexion the patient was advised to straighten at 
his/her same knee while the patient maintained a 
fixed 90° hip flexion position.29,30 The Clinometer 
was then moved to the anterior tibial shaft to 
assess the amount of knee extension which was 
recorded as the AKET measurement, a straight 
knee was considered 90° of movement. The 
standard error of measurement (SEM) has been 
reported at 3.8°.29,30 The Minimal Detectable 
Change (MDC) has been recorded between 9.7° 
and 10.5°.29,30 

Strength Testing  

Manual Muscle Tests were included to grade 
muscular strength during evaluations.31 Each 
patient was positioned prone and queued to flex 
his/her knee through the full ROM. If the patient 
could not move through the full ROM against 
gravity a grade of 2 was documented. No 
patients had a trace amount of movement, grade 
1. When full ROM accomplished against gravity 
with no pain and the same ROM compared 
bilaterally a grade of 3 was documented. Next, 
the TC placed force on the posterior aspect of 
the calcaneus while the patient’s knee was flexed 
to 90° and then asked the patient to resist. If the 
patient was able to resist the same force 
bilaterally a grade of 5 was recorded, grade of 
4 was provided when full ROM was obtained 
but one side was unable to resist the same force 
as the contralateral side.31  

Patient Specific Functional Scale 

For assessment of perceived function, a modified 
PSFS was implemented for uniformity between 

patients and the a priori design. The PSFS 
classified each activity on an 11-point scale with 
10 defined as, able to perform the same as 
before injury. An MCID is established for the 
PSFS when a score for a single activity changes 
by 3 points.32 For the single activity, the patient 
was asked to stand with his/her feet about an 
inch apart and then cued to “bend forward and 
touch your toes”. Following completion of the task 
the patient was asked to score the task on the 
11-point scale. 

RESULTS 

Four patients were evaluated and treated by the 
TC and were discharged to full unrestricted 
activity in an average of 2.75 days from the 
start of treatment (Table 3). During the treatment 
sessions, POE and COE outcomes were collected 
to assess the patient’s pain and function. 
Immediately following the initial treatment all the 
patients reported a decrease in pain that met 
MCID standards and three out of the four 
patients had an increase AKET measurement that 
was greater than the MDC (Table 4). Prior to 
returning to full unrestricted activity (i.e. 
competitive event) the patients had decrease in 
NRS, as well as increases in PSFS, MMT and 
AKET (Table 5 & Table 6). At the one-week 
assessment all the patients reported a MCID for 
NRS and DPAS while all but one had a MCID 
recorded for PSFS (Table 6). The AKET measures 
for each patient were all greater than the MDC 
at the six-week follow-up assessment (Table 5). 
At the six-week follow-up after discharge each 
patient reported no re-injury and maintained 
outcome scores. 

DISCUSSION 

The initial treatment of PRRT resulted in 
immediate improvements on the NRS and AKET 
for all four patients classified with a FNHD 
(Table 4). Applying the PRRT hamstring treatment 
sequence to these patients paired with 
appropriate activity progression (restricted to  



A Novel Approach to Treating Acute Hamstring Functional Neuromuscular  
Disorder-Effects of Primal Reflex Release Technique 

 

 

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All rights reserved. ISSN Online 2577-8188                                                                        Volume 2 – Issue 1 – February 2019  

 

 

 

 

 

 

 

 

 

  

Table 3. Course of Treatment Timeframe 

Patient # Time from Injury 
to Tx (Days) 

Number of 
Tx Sessions 

Limited Participation 
in Sport (Days) 

Discharged 
from Tx (Days) 

Unrestricted 
Activity (Days) 

1 1 3 2 4 3 
2 <1 2 1 3 3 
3 <1 3 2 3 3 
4 <1 2 1 2 2 
Tx = Treatment 

Table 4. Initial Pre-Intervention to Post-Intervention Outcome Scores 

Patient # Pre-Tx 
NRS 

Post-Tx 
NRS 

Pre-Tx 
PSFS 

Post-Tx 
PSFS 

Pre-Tx 
AKET 

Post-Tx 
AKET 

Pre-Tx 
MMT 

Pre-Tx 
MMT 

1 4 2 a 5 8a 55 67b 2/5 3/5 
2 8 6 a 2 4 23 31 2/5 2/5 
3 5 3a 7 8 52 65b 3/5 3/5 
4 7 0a 5 5 62 73b 3/5 3/5 
Tx = Treatment; a= MCID, b= MDC 

Table 5. Outcome Measurements Discharge to 6-Week Follow Up 
Patient # Discharge MMT 1 Week MMT 6 Week MMT 
Clinician Oriented Outcome Measures 
   Manual Muscle Testing  
      1 4/5 4+/5 5/5 
      2 4+/5 5/5 5/5 
      3 5/5 5/5 5/5 
      4 4/5 5/5 5/5 
   Active Knee Extension Test 
      1 67a/65 66/66 72/75 
      2 64a/68 68/70 63/64 
      3 70a/74 78/77 85/85 
      4 73a/77 78/78 71/73 
Patient Oriented Outcome Measures 
   Numeric Rating Scale 
      1 0b 0 0 
      2 2b 1 0 
      3 0b 0 0 
      4 0b 0 0 
   Disablement of the Physically Active  
      1 - 18b 0 
      2 - 0b 0 
      3 - 6b 4 
      4 - 19b 0 
   Patient Specific Functional Scale 
      1 10b 8 10 
      2 10b 10 10 
      3 9 9 8 
      4 9b 8 10 
AKET = affected limb/unaffected limb; a= MDC from discharge to 
unrestricted activity; b= MCID from discharge to unrestricted activity 



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All rights reserved. ISSN Online 2577-8188                                                                        Volume 2 – Issue 1 – February 2019  

unrestricted activity) assisted the patients in 
returning to pre-injury participation levels. The 
focus of the four PRRT treatment techniques was 
on modifying the nervous system rather than a 
muscle tissue healing model which is commonly 
followed after the classification of an acute 
hamstring injury. Treating hamstring injuries with 
neurophysiological based interventions can have 
positive effects on pain, ROM, and function of 
the patient. The results of this case series support 
the use of intervention theories to modulate the 
CNS to assist patients classified with FNHD return 
to normalized allostatic loads demonstrated by 
outcomes improving before expected muscle 
tissue healing timeframes. 

The classification of FNHD was based on the 
Munich muscle injury classification system. This 
system takes into account past classification 
systems based on structural damage and systems 
that explored functional deficits. By adding 
increased specifications for muscle injury, the 
Munich muscle injury classification system supports 
the use of a more patient-centered intervention 
approach. In patients that do not have structural 
muscle damage a FNMD guides clinicians to 
consider the neurological mechanisms of injury, 
which are often overlooked.    

The goals for a patient following a hamstring 
injury is to decrease pain followed by restoring 
normal ROM, strength, and function, while 
minimizing injury recurrence rates.1,2,7,11 Pain 
management is the initial goal of any 
rehabilitation program. Pain could be the 
prolonged symptom that needs to be addressed 
before function can be fully restored.6,11,33,34 
Decreasing pain is commonly achieved through 
heat, ice, ultrasound, electrical stimulation, 
mechanical therapies, and rest.1,2,13,33-35 
Following a decrease in pain, ROM must be 
restored before strength and functional activities 
can improve.35-38 Clinicians assess musculoskeletal 
injuries in this manner based on a hypothesized 
correlation with severity of signs and symptoms. 
Rehabilitation is progressed based on decreased 

signs and symptoms assumed to be associated 
with tissue healing.7,14,36,37 New classification 
systems are warranted as Ekstrand et al., found 
that patients classified with structural injuries 
through clinician evaluation only had evidence of 
MRI diagnosed muscle tear in 29% of patients.39 
No diagnostic imaging was completed during this 
case series. Through an innovative treatment used 
with these patients to modify neural allostatic 
loads, immediate changes in pain and function 
occurred leading to discharge criteria being 
achieved faster than the traditional timeframes 
associated the muscle tissue healing. Each patient 
in this study reported immediate decreases in 
pain at an amount that satisfied a MCID and 
increased ROM greater than a MDC at the one-
week follow-up for each patient (Table 5 & 
Table 6). Immediate changes in pain and ROM 
are useful to clinicians and further research 
should be completed on treatments that have 
similar effects. 

Hamstring injury and re-injury rates have been 
consistent for the past 20 years and have been 
associated with prolonged symptoms in 
physically active populations.3-5, 12 Most 
traditional treatments for acute hamstring injuries 
have been studied in physically active 
populations and include stretching techniques 
paired with strengthening (e.g., eccentric) 
exercises, and trunk stabilization and agility drill 
progressions.13,34, 38 Most of these stretching 
techniques are time consuming and rely on tissue 
change that may not restore neuromuscular 
connections that are also responsible for 
functional deficits. Range of motion increases 
have been linked to sensory perception instead 
of the commonly cited mechanical theories to 
increase muscle extensibility.17,40 Currently, the 
best recommendations do not recommend 
clinicians to consider modifying the neural 
allostatic loads following an acute hamstring 
injury.1,2,13,35-38 To improve on the hamstring 
injury and re-injury rates new innovative 
treatments should be explored. Treatments that 



A Novel Approach to Treating Acute Hamstring Functional Neuromuscular  
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All rights reserved. ISSN Online 2577-8188                                                                        Volume 2 – Issue 1 – February 2019  

attempt to adjust dysregulated neural allostatic 
loads created during a mechanism of 
injury/trauma need to be considered in future 
research, as well as implemented into clinical 
practice. Sherry et al., reported that re-injury 
occurs in one-third of patients within two weeks 
of returning to unrestricted activity from a 
stretching and strengthening hamstring injury 
treatment program.13 None of the patients in the 
current case series suffered re-injury upon 
returning to full team activities at six-week 
follow-up which supports the effectiveness of 
PRRT in a short-term period. 

The nervous system is sophisticated from the 
reflex circuits that occur at the spinal level to the 
descending motor pathways that control 
voluntary movement. Following injury or even 
perceived tissue damage the nervous system 
reacts with reflexes (e.g., flexor reflex, 
autogenic inhibition reflex, myotatic reflex).19,20 
Each of these movements are facilitated by an 
external stimulus and provide sensory 
information to the neurons within the spinal cord 
which result in motor neurons being activated to 
diffuse the external stimulus. When the reflex 
circuit is functioning appropriately the nervous 
system is effective at recognizing and 
responding to potentially dangerous external 
stimuli. However, in some cases external stimuli 
cannot be managed solely by the reflex 
circuit.40,41 The sensory information travels 
through the spinal cord to the brainstem and 
forebrain, which then sends a signal through the 
descending motor pathway to respond to the 
stimulus.19,20,40 If addition sensory information 
continues to ascend to the CNS, the allostatic 
load will remain increased thus leading to 
hypersensitivity of the nervous system. Through 
modulation of the CNS, reflexes can be 
stimulated to modify the allostatic load which 
would potentially result in immediate changes at 
the local site of musculoskeletal injury.22  

There are several programs that are available 
to guide the treatment of acute hamstring injury. 

Sherry et al., provided an outline of differential 
diagnosis, prognosis, and return to play protocol 
for acute hamstring injury.11 This protocol 
recommends 3 phases over eight weeks to 
progress a patient to return-to-activity. The 
return-to-activity was based on pain-free 
palpation over the injury site, full muscle strength, 
full muscle endurance, and no kinesiophobia. 
Patients classified with acute hamstring strain 
return-to-play in a range of 6-22 days.4,7,13 
Gibbs et al., assessed 31 patients classified with 
grade I hamstring strain. Fourteen of the patients 
had normal MRI and returned to full team 
activities at an average of 6 days while 17 
patients averaged 20 days to return to full team 
activities.7 Comparatively, the patients in this 
current study were discharged to return to full 
unrestricted activity and able to complete full 
team activities at 2.5 days. 

With no peer-reviewed articles specific to the 
treatment of patients classified with acute 
hamstring injury, PRRT has been found to have a 
positive effect on pain and function when 
implemented in other areas of the body. 
Hansberger et al. reported a decrease pain in 
patients with chronic and acute plantar fasciitis in 
an intercollegiate athletic training clinic.24 The 
current study employed treatment procedures 
that were similar in design and time for 
intervention to the case series by Hansberger.  
Hansen-Honeycutt et al., reported an immediate 
decrease in musculoskeletal pain in three patients 
using PRRT and breathing reflex triggering 
exercises in a intercollegiate athletic training 
clinic.25 After utilizing these techniques, each 
patient reported a decrease in tenderness to 
palpation over his/her tender areas or with 
primary musculoskeletal complaint.25 The samples 
for both studies were patients in intercollegiate 
athletic training clinics.24,25 A third study was a 
case report on a patient with shoulder 
impingement syndrome treated with PRRT which 
resulted with immediate reduction of POE for 
pain, disablement, and perceived function.26 



A Novel Approach to Treating Acute Hamstring Functional Neuromuscular  
Disorder-Effects of Primal Reflex Release Technique 

 

 

28 
Copyright © by Indiana State University                                                                                Clinical Practice in Athletic Training  
All rights reserved. ISSN Online 2577-8188                                                                        Volume 2 – Issue 1 – February 2019  

These examples of PRRT decreasing or resolving 
pain in 1 to 3 treatments warrants further 
investigation of this technique in other 
musculoskeletal disorders such as acute hamstring 
injury. 

Based on outcomes recorded in the current study, 
treatments focused on modulating the CNS 
warrant further investigation in both clinical and 
laboratory settings that utilize randomized 
controlled methods. As expressed by the results, 
the intervention, PRRT, used in the current case 
series may have been effective at creating ideal 
function of the nervous system instead of a 
healing the tissue based on a myopic muscle 
tissue healing model. Future studies should 
incorporate a larger sample size of patients with 
acute hamstring injury treated and assess the 
effectiveness of PRRT in patients with and without 
MRI evaluated hamstring injuries. To expand on 
the effectiveness of PRRT, cohort studies 
comparing PRRT versus other treatment 
interventions for acute hamstring injury would 
help support if the effects of this study were due 
to the use of PRRT.  

The case series presented was the first to report 
the outcomes of PRRT for treating acute 
hamstring injury. Some of the limitations include a 
small sample size, and no clinician reliability. The 
TC was a novice practitioner with one year of 
clinical application of PRRT and therefore had 
not become an expert at the technique through 
years of practice. The TC providing the treatment 
also obtained measurements (e.g. MMT, ROM) 
and was not blind to results. The patients were 
young, physically active intercollegiate athletes 
therefore the effects may be expected in the 
same population.  

CLINICAL APPLICATION 

Through the case series performed by a certified 
athletic trainer in an athletic training clinic, the 
results of PRRT to treat patients with FNMD were 
reported. In this isolated case series patients, 

had an immediate change in pain and ROM 
following treatment sessions. Treating patients 
classified with FNMD with PRRT led to immediate 
and short-term changes in the POE and COE 
outcomes along with successful return-to-activity. 
The use of PRRT possibly modified the neural 
allostatic load of the patient, which could explain 
the improved patient outcomes in the current 
study. The standard of care for hamstring muscle 
injuries is guided by the goal of creating a tissue 
change to decrease pain, restore function, 
improve strength, and limit reinjury.1,2,7,11 In the 
current study, COE and POE outcomes were 
positively affected in a shorter amount of time 
compared to pathoanatomic healing timeframe 
for similar patients classified with grade 1 
hamstring strain. The available research on PRRT 
supports, through clinic practice outcomes, a 
neurophysiological approach to treatment of 
acute hamstring injury. Based on the outcomes of 
the study, clinicians looking to improve patient 
outcomes may benefit from considering a 
paradigm that modifies the neural allostatic 
loads during treatment prior to or in conjunction 
with other techniques rather than relying solely 
on the pathoanatomical theory of tissue healing. 

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Copyright © by Indiana State University                                                                                Clinical Practice in Athletic Training  
All rights reserved. ISSN Online 2577-8188                                                                        Volume 2 – Issue 1 – February 2019  

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