Muscle injuries are the most common type of injury in many sports: from football and athletics to strength disciplines. The hamstring in a sprinter, the calf muscle in a tennis player, the pectoral muscle in a bench presser — the mechanisms are similar, although the circumstances differ. The editorial team examined what happens during a muscle tear, why it occurs and how pharmacology affects the risk.
What a muscle tear is and how it is classified
A muscle tear is understood as mechanical damage to muscle fibres, from microscopic to a complete tear of the muscle or its avulsion from the tendon. In everyday life people often speak of a "strain", but from a medical point of view this too is fibre damage, only on a smaller scale.
Epidemiological studies of professional football conducted by the group of J. Ekstrand showed that muscle injuries make up about a third of all injuries, and the muscles of the hamstring suffer most often (Ekstrand et al., 2011). A similar picture is observed in other sports with sprinting.
There are several classifications for describing muscle injuries. The Munich consensus separates functional disorders (fatigue-related, neuromuscular disorders, soreness) and structural damage — partial and complete tears (Mueller-Wohlfahrt et al., 2013). The British Athletics system grades the degree of injury by MRI data and separately indicates whether the tendon is involved (Pollock et al., 2014).
Refining the classification has practical significance: injuries involving the intramuscular tendon, as a rule, heal longer and recur more often than damage to muscle tissue alone.
| Type of damage | What happens | Typical manifestations |
|---|---|---|
| Functional disorder | Without macroscopic tear | Tension, soreness, stiffness |
| Partial tear (minor) | Damage to a small part of the fibres | Local pain, moderate limitation |
| Partial tear (moderate) | A significant part of the muscle's cross-section | Pronounced pain, weakness, bruising |
| Complete tear / avulsion | Complete disruption of integrity | Defect, loss of function, haematoma |
Mechanism of injury: why a muscle tears
Most muscle tears occur during an eccentric contraction — when a muscle tenses and at the same time lengthens under an external force. The classic example is the hamstring at the end of the leg-swing phase in sprinting: the muscles brake the movement of the shin while being maximally stretched.
The most vulnerable muscles are two-joint ones, that is, those that pass through two joints: the biceps femoris, the rectus femoris, the calf muscle. Their length changes simultaneously at two joints, which increases the mechanical load.
Most often a tear occurs in the zone of the muscle-tendon junction — the transition of muscle tissue into tendon. This area combines tissues of different stiffness, and the concentration of stress here is maximal.
In strength sports the mechanism is different: a tear occurs during a maximal effort with heavy weight, for example in the bench press, when the pectoral muscle is in a stretched position. In such a case it is predominantly a matter of avulsion of the tendon of the pectoralis major from the humerus.
Load and risk factors
The strongest known risk factor for a muscle tear is a previous injury of the same muscle. Scar tissue differs in its properties from healthy tissue, and incomplete rehabilitation leaves a deficit of strength and flexibility. That is why a hasty return to sport is one of the main causes of repeat tears.
Fatigue increases the risk: in football, muscle injuries occur more often at the end of halves and during periods of a congested calendar. A tired muscle absorbs energy worse and controls movement worse.
Sharp changes in load — for example, a sudden addition of sprinting work after a long period of slow running — also create risk. Muscles not prepared for maximal speeds or weights are injured more often. Conversely, regular contact with high-speed running in training is regarded as a protective factor.
Other factors include age, insufficient eccentric strength, imbalance between antagonist muscles, insufficient warm-up, cold weather conditions. Recent studies also draw attention to sleep deprivation and general fatigue as additional factors.
- a previous injury of the same muscle;
- fatigue and a congested competition schedule;
- a sharp increase in speed or strength load;
- insufficient eccentric strength;
- age and incomplete rehabilitation after previous injuries.
Pharmacology and the risk of muscle tears
Anabolic steroids are the most discussed group in the context of tears in strength sports. They quickly increase muscle strength, but the tendons and their attachment zone adapt more slowly. A study among experienced strength athletes found a higher frequency of tendon ruptures in steroid users (Kanayama et al., 2015). Case reports of avulsion of the pectoralis major tendon in athletes who used steroids appear in the literature regularly.
Statins — drugs for lowering cholesterol — can cause muscle symptoms, from pain to rare but dangerous rhabdomyolysis. People who take statins and do intense sport should discuss with a doctor the appearance of muscle pain, weakness or darkening of the urine.
Diuretics and sharp dehydration before weigh-in disrupt the balance of fluid and electrolytes, which is associated with cramps and, probably, with increased muscle vulnerability. Fluoroquinolones deserve separate mention, as they primarily affect tendons.
Finally, painkilling injections and high doses of anti-inflammatory agents before competitions allow one to perform with pain, which masks already existing damage. Such a practice can turn a minor injury into a complete tear.
Typical muscle injuries in different sports
In football, rugby, sprinting and other sports with maximal speeds, hamstring injuries predominate. The rectus femoris is injured when kicking the ball, and the adductor muscles when making sharp changes of direction.
The calf muscle, especially its medial head, is injured in tennis, squash and running over rough terrain. Such a tear has even acquired the name "tennis leg".
In powerlifting, bodybuilding and CrossFit, tears of the pectoralis major, the distal biceps tendon and the quadriceps femoris are characteristic. These injuries often require surgical treatment.
Knowing the "typical" injuries of your sport helps to build prevention purposefully: to strengthen the corresponding muscles, work on eccentric strength and control the load in the riskiest exercises.
Editorial conclusions
A muscle tear most often occurs during an eccentric contraction of two-joint muscles, predominantly in the zone of the muscle-tendon junction.
The main risk factors are a previous injury, fatigue, sharp changes in load and insufficient eccentric strength.
Anabolic steroids create an imbalance between muscle strength and tendon strength, statins can cause muscle damage, and painkilling injections mask damage.
We also recommend reading our materials on the prevention and diagnosis of muscle tears, on tendinitis in athletes and on tendon ruptures.
References
- Ekstrand J, Hägglund M, Waldén M. Epidemiology of muscle injuries in professional football (soccer). Am J Sports Med. 2011;39(6):1226–1232.
- Mueller-Wohlfahrt HW, Haensel L, Mithoefer K, et al. Terminology and classification of muscle injuries in sport: the Munich consensus statement. Br J Sports Med. 2013;47(6):342–350.
- Pollock N, James SL, Lee JC, et al. British athletics muscle injury classification: a new grading system. Br J Sports Med. 2014;48(18):1347–1351.
- Kanayama G, DeLuca J, Meehan WP 3rd, et al. Ruptured tendons in anabolic-androgenic steroid users: a cross-sectional cohort study. Am J Sports Med. 2015;43(11):2638–2644.
- Pope HG Jr, Wood RI, Rogol A, et al. Adverse health consequences of performance-enhancing drugs: an Endocrine Society scientific statement. Endocr Rev. 2014;35(3):341–375.
- van der Horst N, Smits DW, Petersen J, et al. The preventive effect of the Nordic hamstring exercise on hamstring injuries in amateur soccer players: a randomized controlled trial. Am J Sports Med. 2015;43(6):907–915.
Andriy Melnyk
A strength-sports coach and author of programs for beginner and intermediate levels. Writes about training planning.
