Muscle Strain

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Introduction

Muscle injuries account for the most frequent cause of disability in sports. Muscle strains occur when muscle fibers cannot cope with the demands placed on them by exercise overload and leads to tearing of the fibers. It is a contraction-induced injury in which muscle fibers tear due to extensive mechanical stress. This usually occurs as a result of a powerful eccentric contraction or over-stretching of the muscle. Therefore, it is typical for non-contact sports with dynamic characteristics such as sprinting and jumping.

In athletes with systemic metabolic disorders and steroid use, spontaneous ruptures have been noted.

Muscle Injury Classification

Muscle lesions are classified as grade I, II, and III based on the amount of fibers disrupted according to clinical and imaging investigations:

Grade I (mild) strains affect only a limited number of fibers in the muscle. There is no decrease in strength and there is a fully active and passive range of motion. Pain and tenderness are often delayed to the next day.
Grade II (moderate) strains have nearly half of muscle fibers torn. Acute and significant pain is accompanied by swelling and a minor decrease in muscle strength.
Grade III (severe) strains represent the complete rupture of the muscle. This means either the tendon is separated from the muscle belly or the muscle belly is actually torn in 2 parts. Severe swelling and pain and a complete loss of function are characteristic of this type of strain.

The above classification is the traditional muscle injury grading by consensus in Munich. Read the full article here:

The table below provides an overview of some of the newer muscle injury classification systems:

Comparison of recent muscle injury classification systems
Chan et al., 2012	Mueller-Wolfahrt et al., 2013	Pollock et al., 2014	Valle et al., 2017	Prakash et al., 2018
Grading based in radiological finding and site of lesion I = Proximal musculotendinous junction II = Muscle A = Proximal B = Middle C = Distal a = Intramuscular b = Myofascial c = Myofascial/perifascial d = Myotendinous e = Combined III = Distal musculotendinous junction	A. Indirect muscle disorder/injury Functional muscle disorder Type 1: Overexertion-related muscle disorder 1A Fatigue induced muscle disorder 1B Delayed onset muscle soreness (DOMS) Type 2: Neuromuscular muscle disorder 2A Spine-related neuromuscular 2B Muscle-related neuromuscular Structural muscle injury Type 3: Partial muscle tear 3A Minor partial muscle tear 3B Moderate partial muscle tear Type 4: (Sub)total tear Subtotal or complete muscle tear Tendinous avulsion B. Direct muscle injury Contusion Laceration	Grade 0: Referred pain 0a - focal muscle soreness with normal MRI 0b - generalised muscle soreness (DOMS) with normal MRI Grade 1 - small injuries to the muscle a = myofascial injury b = muscle or musculotendinous junction c = tendon involvement Grade 2 - Moderate injuries (tears) a = myofascial injury b = muscle or musculotendinous junction c = tendon involvement Grade 3 = Extensive tears a = myofascial injury b = muscle or musculotendinous junction c = tendon involvement Grade 4 = Complete tears a = myofascial injury b = muscle or musculotendinous junction c = tendon involvement	Mechanism of injury (M) D = Direct I = Indirect Location of Injury (L) P - injury located in proximal third of muscle belly M - injury located in the middle third of muscle belly D - injury located in the distal third of the muscle belly Grading of severity (G) 0 -3 based on MRI No of muscle re-injuries (R) 0 - 1st episode 1 - 1st re-injury 2 - 2nd re-injury...	MRI-based grading Grade 0 - oedema or fluid adjacent to intact connective tissue, no myofibril detachment Grade 1 - myofibril detachment without connective tissue change Grade 2 - myofibril detachment with adjacent connective tissue increased signal, delamination or defect, but no retraction Grade 3 - myofibril detachment with adjacent connective tissue retraction indicating failure

Predisposing Factors

Three types of muscle are at higher risk of injury:

• Two-joint muscles. Specifically, the motion at one joint increases the passive tension of the muscle and leads to an overstretching injury. Two-joint/biarthrodial muscles have less ability to withstand tension.
• Muscles contracting eccentrically. When muscles undergo eccentric (lengthening) contractions, they are more easily injured compared to when performing isometric or concentric contractions. Eccentric contractions, frequent during the deceleration phase of activity, cause higher forces on muscle fibers as opposed to concentric contractions.
• Muscles with a higher percentage of type II fibers. These are fast-twitch muscles that develop high- speed contractions. In this way, the muscle is more predisposed to injury. Most of the muscle activity in running and sprinting is eccentric, explaining why such strains most often occur in sprinters or ‘speed athletes’. The hamstrings, gastrocnemius, quadriceps, hip flexors, hip adductors, Erector Spinae, deltoid, and rotator cuff are most commonly injured.

The video below gives a good summary of the salient points

Signs and Symptoms

Symptoms of muscle strain include:

• Swelling, bruising, or redness due to the injury
• Pain at rest
• Inability to use the muscle at all
• The weakness of the muscle or tendons
• Palpable gap in the muscle

Risk Factors

Strains are not restricted to athletes and can happen while doing everyday tasks, although athletes are more at risk for developing a strain. It is common for an injury to occur alongside a sudden increase in duration, intensity, or frequency of activity.

Treatment of Acute Strains

Severity of muscle strain, and what function or loads your injured muscle will need to cope with, will impact the length of your healing and rehabilitation process.

The first-line treatment for a muscular strain in the acute phase includes five steps commonly known as P.R.I.C.E.

• Protection: Apply soft padding to minimize impact with objects.
• Rest: Rest is necessary to accelerate healing and reduce the potential for re-injury.
• Ice: Apply ice to induce vasoconstriction, which will reduce blood flow to the site of injury. Never ice for more than 20 minutes at a time.
• Compression: Wrap the strained area with a soft-wrapped bandage to reduce further diapedesis and promote lymphatic drainage.
• Elevation: Keep the strained area as close to the level of the heart as is possible in order to promote venous blood return to the systemic circulation.

The first treatment is usually an adjunctive therapy of NSAIDs and Cold compression therapy. Cold compression therapy acts to reduce swelling and pain by reducing leukocyte extravasation into the injured area. NSAIDs such as Ibuprofen/paracetamol work to reduce the immediate inflammation.

New treatments are an expanding area. A growing number of health care professionals are using biological factors to favor the healing of muscle injuries. However despite relatively widespread use, the scientific evidence behind such products is scanty, and the results probably less dramatic than what reported in the lay literature. The use of platelet-rich- plasma (PRP) injections which have been shown to accelerate recovery from non-surgical muscular injuries.

In the second phase, early mobilization must has been shown to improve injured skeletal muscle regeneration.However, it is important to note that immediately mobilising after injury has been shown to increase the risk of re-rupture. Therefore, a brief immobilisation period with bandages is recommended - this rest period allows the scar tissue to connect to the muscle failure.

The cardiovascular conditioning program should be performed with a low impact. Since core stability programs have been shown to improve results in terms of lower re-injury rates and enhanced return to play, they must be introduced along with the specific rehabilitation program of the injured muscle.

Proprioceptive and endurance training is used in the advanced stages of rehabilitation. After the athlete has regained full, pain-free active ROM and over 90% strength bilaterally, full participation is allowed. The maintenance programs should be continued to avoid any dysfunctional adaptation or compensation.

Example Rehab program guidelines:

1. Applying heat to the strained muscle may be helpful - any rehab should begin with heating of the injured muscle.
2. Passive and active stretching program - stretching distends mature scar tissue during the early phase when it is still plastic. Pain-free stretches can be gradually progressed, starting with periods of 10 to 15 seconds and then progressing to 1 minute.
3. Isometric training, progress with use of weights. Isometrics should be painless
4. When isometric training with weights can be achieved painlessly, move on to isotonic exercises
5. Isokinetic exercises with minimum load once steps 3 and 4 can be achieved painlessly

Treatment guidelines according to grading:

Grade 1: Despite no/minimal loss of strength, small amounts of swelling and limited disability, maintenance of activity is not recommended due to the high risk of worsening the injury.

Grade 2: The healing process usually lasts for around 2-3 weeks, and it is recommended that the patient returns to physical activity after around 1 month, albeit gradually and carefully.

Grade 3: For complete rupture, surgery is the preferred choice. After surgical repair, patients have the knee immobilized for 4 to 6 weeks. Requires intense rehabilitation for long periods of up to 3 to 4 months. Even after treatment of the lesion, the patient may continue to have some pain for months.