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Football (soccer) is classified among sports with a high traumatic risk. This is unequivocally confirmed by a great number of epidemiological studies. Indeed, the percentage of professional male players suffering an injury during a sporting season is between 65 and 91% (Walden et al. 2005). From an epidemiological point of view, in the football player, the anatomical location recording the greatest number of injuries is the thigh, followed by the ankle joint, the pubic area, and the knee joint. The injuries of the thigh flexor muscles (classified in the Anglo-Saxon nomenclature with the collective term of hamstring) represent, among the muscle-tendon injuries, the most recurrent trauma, accounting for about 17% of all injuries. This type of injury is so frequent that a typical team of 25 players can statistically expect about seven hamstring injuries for each season (Ekstrand et al. 2011a, b). This results in approximately 2 weeks of training and competition lost for each injury event (Eirale and Ekstrand 2013). In terms of exposure per 1000 hours of play, the incidence of indirect hamstring injuries is 0.87–0.96/1000 hours. This epidemiological data show that hamstring injuries are the source of a significant absence for the players from both training and competition (Mendiguchia et al. 2012; Orchard et al. 2013). Hamstring injuries are linked to the interaction of numerous risk factors that can be divided into two categories: non-modifiable and modifiable risk factors (Crosier 2004; Kellis et al. 2012; Kellis 2018; Bisciotti et al. 2020).

The hamstring muscle complex (Fig. 9.1) is comprised of three different muscles: semitendinosus, semimembranosus, and biceps femoris.

Background Although performance of the Nordic hamstring exercise (NHE) has been shown to elicit adaptations that may reduce hamstring strain injury (HSI) risk and occurrence, compliance in NHE interventions in professional soccer teams is low despite a high occurrence of HSI in soccer. A possible reason for low compliance is the high dosages prescribed within the recommended interventions. The aim of this review was to investigate the effect of NHE-training volume on eccentric hamstring strength and biceps femoris fascicle length adaptations. Methods A literature search was conducted using the SPORTDiscus, Ovid, and PubMed databases. A total of 293 studies were identified prior to application of the following inclusion criteria: (1) a minimum of 4 weeks of NHE training was completed; (2) mean ± standard deviation (SD) pre- and post-intervention were provided for the measured variables to allow for secondary analysis; and (3) biceps femoris muscle architecture was measured, which resulted in 13 studies identified for further analysis. The TESTEX criteria were used to assess the quality of studies with risk of bias assessment assessed using a fail-safe N (Rosenthal method). Consistency of studies was analysed using I2 as a test of heterogeneity and secondary analysis of studies included Hedges’ g effect sizes for strength and muscle architecture variables to provide comparison within studies, between-study differences were estimated using a random-effects model. Results A range of scores (3–11 out of 15) from the TESTEX criteria were reported, showing variation in study quality. A ‘low risk of bias’ was observed in the randomized controlled trials included, with no study bias shown for both strength or architecture (N = 250 and 663, respectively; p I2 = 62.49%) and muscle architecture (I2 = 88.03%). Within-study differences showed that following interventions of ≥ 6 weeks, very large positive effect sizes were seen in eccentric strength following both high volume (g = 2.12) and low volume (g = 2.28) NHE interventions. Similar results were reported for changes in fascicle length (g ≥ 2.58) and a large-to-very large positive reduction in pennation angle (g ≥ 1.31). Between-study differences were estimated to be at a magnitude of 0.374 (p = 0.009) for strength and 0.793 (p Conclusions Reducing NHE volume prescription does not negatively affect adaptations in eccentric strength and muscle architecture when compared with high dose interventions. These findings suggest that lower volumes of NHE may be more appropriate for athletes, with an aim to increase intervention compliance, potentially reducing the risk of HSI.

Hamstring and calf injuries are common in athletes and may cause significant functional impairment. Etiologies range from acute strains to chronic overuse conditions. Accurate determination of injury location, severity, and mechanism is important for proper triage, treatment planning, and return to play discussions. This chapter describes the most common hamstring and calf injuries encountered in clinical practice: acute hamstring strains, proximal hamstring tendinopathy, distal hamstring injuries, gastrocnemius and soleus strains, medial tibial stress syndrome, chronic exertional compartment syndrome, and plantaris tendon ruptures. Specific injury characteristics, diagnostic features, and treatment recommendations are described for each condition. Most of these injuries can be managed effectively with appropriately targeted nonoperative strategies.

Hip, pelvis, and core injuries are common in football players. These injuries are difficult to discern, leading to inaccurate diagnoses, delayed treatment, and prolonged recovery. To successfully manage theses injuries, one must have a firm understanding of the complex anatomic relationships of the hip, core, and pelvis. A thorough history and physical examination and a general knowledge of common athletic conditions are equally important to ensuring accurate diagnosis and appropriate treatment. This chapter discusses the diagnosis, treatment, and outcomes of common athletic hip pathology.

While posterior knee injuries in isolation are rare, they certainly can cause persistent pain and disability when overlooked. In addition, posterior knee region anatomy is complex and tendon injuries in this area can easily be mistaken as an intra-articular pathology. Awareness of posterior knee region tendon injuries allows health care providers to effectively manage these pathologies without delay in care. This chapter discusses the posterior knee tendon anatomy, pathologies, work up, and management. The majority of treatments for most tendon lesions in this area are non-surgical although surgical intervention is discussed.

While using a single four-strand semitendinosus tendon posterior harvesting, we make sure we adopt a mini-invasive technique with minimal scars and less postoperative morbidity. It is a very demanding technique, but quite easily reproducible once we respect each step. In this chapter, we describe every step of this mini-invasive technique while describing how to avoid the pitfalls using simple tricks.

ACL reconstruction with quadruple bundle gracilis and semitendinosus is the most common ACL procedure due to its simplicity and lesser morbidity related to graft harvesting. Like in all techniques, the time dedicated to the graft harvesting is paramount. The quality of the graft dictates the long-term results of the ACL reconstruction. In this chapter, we shall also place emphasis on the well positioning of the femoral tunnel because an anteriorly positioned femoral tunnel is the number one cause of ACL failure.

Stress reactions of the pars interarticularis is termed spondylolysis and plays a major role in debilitating back pain in the adolescent athlete. While many athletes will rest and ultimately improve, the adolescent who ignores their symptoms may experience persistence or worsening back pain and may ultimately develop other signs such as hamstring tightness or neurologic compromise. While imaging modalities have been scrutinized, recent algorithms have been published to guide evaluation. Surgical management is reserved for cases that do not respond to conservative treatment, or in those with neurologic compromise. Outcomes are generally favorable, though surgeons should be aware of the potential complications.

Injuries to the proximal hamstring are common, including injuries to the myotendinous junction, the proximal free tendon, or the ischial apophysis. Uncomplicated injuries often can be diagnosed by history and examination, without the need for imaging, though magnetic resonance imaging (MRI) and ultrasound (US) have utility in cases where there is weakness or prolonged recovery. Most hamstring conditions, including myotendinous injuries and proximal hamstring tendinopathy, can be treated non-operatively using a graded rehabilitation approach. Here we review the types of injury, risk factors, clinical presentation, diagnosis, treatment options, and prognosis for proximal hamstring injuries.

Platelet-rich plasma (PRP) has myriad applications for management of injury in high-level American football players. Each game missed can have a significant impact on an athlete’s ability to maintain depth chart position or advance to the next level of competition with potentially significant financial implications. In this chapter, we will review background scientific information on PRP and its use in sports injuries, while also highlighting our PRP experience at a National Collegiate Athletic Association (NCAA) Division I football program. We will discuss the use of PRP for in-season management of specific injury patterns commonly seen in elite football athletes, especially with our extensive clinical experience with hamstring strains, and focus on return to play, avoidance of adverse injection reactions, and recurrent injury.

Background Given the severe economic and performance implications of hamstring injuries, there are different attempts to identify their risk factors for subsequently developing injury prevention strategies to reduce the risk of these injuries. One of the strategies reported in the scientific literature is the application of interventions with eccentric exercises. To verify the effectiveness of these interventions, different eccentric strength measurements have been used with low-cost devices as alternatives to the widespread used isokinetic dynamometers and the technically limited handheld dynamometers. Therefore, the purpose of the present systematic review was to summarize the findings of the scientific literature related to the evaluation of eccentric strength of hamstring muscles with these new technologies. Methods Systematic searches through the PubMed, Scopus, and Web of Science databases, from inception up to April 2020, were conducted for peer reviewed articles written in English, reporting eccentric strength of hamstrings assessed by devices, different to isokinetic and handheld dynamometers, in athletes. Results Seventeen studies were finally included in the review with 4 different devices used and 18 parameters identified. The pooled sample consisted of 2893 participants (97% male and 3% female: 22 ± 4 years). The parameters most used were peak force (highest and average), peak torque (average and highest), and between-limb imbalance (left-to-right limb ratio). There is inconsistency regarding the association between eccentric hamstrings strength and both injury risk and athletic performance. There is no standardized definition or standardization of the calculation of the used parameters. Conclusions The current evidence is insufficient to recommend a practical guide for sports professionals to use these new technologies in their daily routine, due to the need for standardized definitions and calculations. Furthermore, more studies with female athletes are warranted. Despite these limitations, the eccentric strength of hamstring muscles assessed by different devices may be recommended for monitoring the neuromuscular status of athletes.

Acute and chronic hamstring injuries are common in athletics. Acute injuries account for 17.1% of all injuries. Chronic injuries (proximal hamstring tendinopathy) are seen less frequently, however, but true incidences are unknown. Acute injuries occur at the (from most frequent to less frequent) musculotendinous junction (MTJ), the intramuscular tendon and the free tendons (partial- or full-thickness injury). Proximal hamstring tendinopathy occurs in the proximal hamstring free tendons. Diagnosis of these injuries is mostly clinical but can be supported by imaging such as magnetic resonance imaging or ultrasound. Treatment for partial-thickness MTJ acute hamstring injuries is informed by 14 RCTs. For proximal hamstring tendinopathy and partial- or full-thickness free tendon injuries, there is little evidence to guide treatment. Cornerstone of treatment is physiotherapy-based interventions with progressive (eccentric) loading and activity modification, combined with expectation management. Surgery is usually reserved for full-thickness free tendon injuries. Other treatments such as platelet-rich plasma injections, corticosteroid injections and non-steroidal anti-inflammatory medication have little supportive evidence and should be avoided.

The anterior cruciate ligament (ACL) is the primary restraint to anterior tibial translation of the knee, and the posterior cruciate ligament (PCL) is the primary restraint to posterior tibial translation of the knee. ACL reconstruction with hamstring or patellar tendon autograft has been the gold standard surgical option for ACL ruptures for many years. Injuries to the PCL in isolation are rare and often managed conservatively although most PCL injuries occur in the multiligament knee injury setting where surgery is indicated, most commonly with a PCL reconstruction. In addition, operative management is indicated in Grade III PCL tears and chronic tears which are symptomatic. ACL and PCL repair techniques have been described in previous literature with variable results. Internal bracing with suture tape augmentation acts as a secondary stabiliser, encouraging natural healing and allowing early mobilisation. This chapter describes internal bracing of the ACL and PCL with suture tape augmentation.

This case of a hockey player with a back injury that is not improving illustrates the need to consider medical causes of musculoskeletal pain in athletes. The young athlete in this case presents for evaluation of low back pain 4 months after a fall in hockey; he is not improving in physical therapy as expected. In addition, he is complaining of symptoms such as morning stiffness, widening area of pain, and weight loss that are inconsistent with a lingering musculoskeletal injury.

We present a case of a young teenager with multiple risk factors for his mechanical low back pain, including increased body mass index, physical inactivity, core instability, and hamstring tightness. There is a known association between both obesity/overweight and sedentary lifestyles and low back pain. Fortunately, exercise can be effective for improvements in low back pain in these populations. The core itself is comprised of abdominal, spinal, pelvic floor, and diaphragm musculature. Core stability is dependent on the interaction of three interdependent systems: the osseoligamentous, the musculature, and the neural control systems. These control the motion of the spine both at end-range and within a “neutral zone” of motion. Specific examination maneuvers and clinical observations of a patient’s posture and mobility can determine the patient’s core stability or instability. Core stabilization exercises may improve core stability and low back pain symptoms. Finally, hamstring tightness has been shown in some studies to be associated with low back pain; therefore, hamstring tightness is important to evaluate and treat.

Chronic proximal hamstring tendon tears represent a diagnostic and therapeutic challenge for treating physicians. Tears involving two or more tendons may benefit from early surgical intervention. Special considerations applicable to the repair of chronic tears include sciatic neurolysis and graft augmentation. This chapter discusses the diagnosis of chronic proximal hamstring tears, surgical indications and technique, rehabilitation, and outcomes.

Hamstring injuries are some of the most frequently occurring injuries experienced by athletes of all levels. They can result in a significant amount of time away from play and have a high rate of recurrence. Some sports confer a higher risk of injury, specifically, ballistic or sprint sports such as rugby, football, and soccer. Similarly, sports such as dance and waterskiing require high risk positioning in deep hip flexion with concurrent knee extension and lead to a high incidence of hamstring injury. Kinematic studies have suggested that these injuries typically occur in late swing phase, when the hamstrings are contracting eccentrically, at or near their maximal length. Multiple classification systems have been described, with various points of focus, to aid the practitioner in guiding treatment and anticipating prognosis.

Surgical treatment of proximal hamstring injuries is recommended for complete tears, partial or complete tears that fail to improve with conservative treatment osseous avulsions with retraction. Both endoscopic and open repair techniques have been described in the literature and in earlier chapters. Currently, endoscopy is indicated for acute or chronic tears with

Proximal hamstring tendon tears are a common injury among athletes and can result in a chronic condition that is difficult for a clinician to manage. Treatment options for patients who can be managed nonoperatively are limited. Biologic is a therapy that has found a place in the nonsurgical treatment arsenal. Biologics augment tendon healing by modulating cellular activity. Platelet-rich plasma is a product derived from the host patient and is rich in growth factors and chemotactic molecules that improve the early stages of tendon healing. Clinical studies of PRP in proximal hamstring tendon injury show promise with reported improvements in pain and function. Future studies are required to evaluate the full potential, but PRP can be useful in patients with chronic hamstring tendinopathy who have failed other conservative measures.

Acute repair of proximal hamstring tears is indicated for high demand athletes and active individuals with multiple tendon involvement with retraction. Acute repairs can be performed endoscopically or through an open surgical technique. There are risks and benefits of each surgical approach in terms of exposure and visualization, potential injury to neurovascular structures, quality of repair, and cosmesis. Early published results suggest that both techniques can provide excellent outcomes with limited complications.

Proximal hamstring tears are rare, but devastating injuries among highly active athletes, most notably water-skiers. The best available evidence estimates that some form of complication occurs in one in five of these surgical repairs, making these injuries (and their complications) topics worthy of further study. These complications, most commonly occurring in the form of neurologic injury or persistent postoperative pain, have potentially serious consequences, and are generally avoidable. Surgeons can aim to avoid these complications through use of a detailed history and physical exam, proper preoperative imaging, and superb understanding of regional anatomy. The purpose of this chapter, then, will be to discuss the best available evidence on proximal hamstring tears and the relative rates of complications associated with their surgical repair.

Hamstring injuries are commonly encountered by orthopedic surgeons and remain one of the more difficult injuries to treat with high probability of recurrence. Proximal hamstring injuries (PHI), not as commonly seen, still provide difficulty and require either nonoperative or surgical treatment. With sports participation continuing to increase, especially among older individuals who remain physically active, prevention and rehabilitation are extremely important. Several sports and other mechanisms have been associated and identified as risk factors for PHI. Anatomic and neuromuscular variations have been described in PHI, which have been targeted for correction during rehabilitation. Most PHI are treated surgically; however, some are treated nonsurgically. There is limited data available on nonoperative outcomes with even more limited information regarding nonoperative rehabilitation and prevention. Further research is necessary to identify which risk factors are unique to PHI and what nonoperative rehabilitation protocol is most effective.

Endoscopic proximal hamstring repair is an emerging technique that is gaining popularity. Currently there are several surgical techniques published on how to perform endoscopic proximal hamstring repairs. In this chapter, we discuss our surgical technique on how to perform an endoscopic proximal hamstring repair. Additionally, we detail the advantages and disadvantages, the pearls and pitfalls, and our postoperative protocol for endoscopic proximal hamstring repair.

Proximal hamstring injuries are particularly challenging. Compared to their more distal counterparts, proximal hamstring injuries have been shown to more severely affect patients’ daily life activities and carry longer recovery periods. If nonoperative treatment is selected, numerous options exist, including various types of physical therapy, non-steroidal anti-inflammatories, steroid and platelet-rich plasma injections, and shockwave therapy. These can be used in isolation, or together. Outcomes for appropriately selected nonoperative patients are generally moderate-to-good, though as noted, recovery time can be extensive. Athletes must be counseled appropriately, and reasonable expectations should be set regarding prognosis and return to play.

Focusing on postoperative rehabilitation following proximal hamstring tears is critical for restoring form, function, and giving the patient the best possible chance of returning to his/her pre-injury level of activity. Prior to surgery, it is vital for the surgeon to manage patient expectations with respect to the timeline of their recovery and ability to return to sports. The main goals of postoperative rehabilitation should be to protect the site of repair during its healing process, ensure restoration of function, prevent the recurrence of symptoms, and control the patient’s pain. While various principles of rehabilitation have been studied (e.g. adjunctive therapies, range of motion and weight-bearing guidelines, exercise progression, etc.), there is debate as to which strategies are optimal for rehabilitation and can allow for safe return-to-play. The purpose of this chapter is to discuss what is currently known about rehabilitation following proximal hamstring tear repairs, as well as discussing current practices.

To effectively rehabilitate hamstring muscle injuries, it is imperative that the clinician perform efficient history taking and a physical assessment. The physical assessment evaluates findings of palpation, range of motion, muscle function, and athletic performance. The information garnered during this process is integrated with the patient’s subjective report and is critical in identifying relevant impairments and deficiencies to be addressed during prevention and rehabilitation. The goal of this chapter is to assist the clinician in performing a valid and reliable clinical assessment in a logical manner to create the foundation for a prevention and/or rehabilitation process targeting the individual athlete.

Currently, effective hamstring injury prevention is primarily based on exercise strategies. The FIFA 11+ is a general strength and conditioning programme that has been shown to reduce injuries in football, including hamstring injuries. Many hamstring injury prevention studies have shown that eccentric hamstring strength training can reduce the risk of sustaining a hamstring injury, with a particular emphasis in the literature on the Nordic hamstring exercise. However, exercise-based prevention can only be effective when adhered to. Meticulous planning, a gradual increase of eccentric training loads for each individual athlete and stimulating adherence through knowledge transfer are key components to make hamstring injury prevention work in a practical setting. So far, evidence from studies that have investigated stretching and plyometric interventions indicate that these interventions do not seem to be effective at reducing hamstring injuries. Research on other types of preventive strategies, such as running drills, core stability training and sports-specific training, is currently insufficient, and the value of these approaches in hamstring injury prevention remains unclear. This chapter aims to provide a detailed understanding of the available evidence for hamstring injury prevention and the practical considerations around implementing these prevention strategies.

This chapter describes the common presentations of muscle strains in the lower limb, beginning from the groin and sports hernias and ending with plantaris strains of the lower leg. Each muscle group and compartment presented in this chapter presents with its most common injury and most common muscle: the biceps femoris of the hamstring, the rectus femoris of the quadriceps, and the gastrocnemius muscle of the calf. In addition to these commonly presented injuries, the chapter commences with an understanding of grading of muscle strains in anatomical, clinical, and imaging description.

Children with cerebral palsy often encounter restricted mobility as a result of knee pathology. Spasticity and imbalance of the lower extremity musculature frequently impair normal knee motion during gait. Hamstring and rectus femoris spasticity, in addition to knee flexion contractures, may result in progressive difficulty with ambulation. Physical examination and computerized motion analysis are useful tools to identify knee pathology, so appropriate treatment strategies may be implemented to improve gait. There are multiple surgical techniques that may be used to improve knee range of motion and preserve knee function throughout a child’s growth.

In practice, three clinical scenarios can be distinguished in hamstring injuries: (1) acute hamstring injury, (2) hamstring injury sequela (repeated episodes of injury and/or pain) and (3) hamstring tendinopathy.

Treatment failure is defined as an unsuccessful result of management, and this is observed frequently in acute and long-standing hamstring injuries. The main causes of treatment failure are an incorrect diagnosis or inefficacy of treatment. This chapter will describe the differential diagnoses that can be considered in patients with treatment failure after acute and long-standing hamstring injuries. Reevaluation of the patient and expanding diagnostic workup can be useful to identify other causes of posterior thigh or buttock pain. If the diagnosis remains within the category of acute hamstring injury, hamstring injury sequela, or hamstring tendinopathy, alternative treatments can be considered. Numerous alternative treatment options are available for this patient group. This chapter describes which treatments can be considered and what the current level of evidence for their efficacy is.

The main aim of hamstring injury rehabilitation is to facilitate that the athlete is returning to sport at highest possible performance level as fast as possible but with a minimal risk of reinjury. The characteristics and presentation of the different hamstring injury types may guide the clinician toward a specific and appropriate rehabilitation plan, including rehabilitation goals with adequate progression and loading through stepwise rehabilitation phases. This chapter summarizes the evidence for hamstring rehabilitation programs following athletic hamstring injuries. The chapter covers acute hamstring muscle injuries, complete hamstring tendon avulsion ruptures, apophyseal avulsion fractures, and proximal hamstring tendinopathies. It further provides recommendations for how to optimize the rehabilitation process for the specific hamstring injury types.

A hamstring strain injury has long been considered as a skeletal muscle injury, and the connective tissue associated with the muscle, i.e., the tendon/aponeurosis, has not been addressed sufficiently. A hamstring strain is a traumatic injury which very often occurs at the myotendinous junction (MTJ), which is the interface between the muscle and the tendon. The MTJ is formed during development and animal research clearly shows the interdependence and interaction between the muscle-derived and the connective tissue-derived cells during developmental processes. Additionally, several key molecules are indispensable for the MTJ formation. Although the MTJ is the most affected site after a strain injury, the research in adaptations to loading, unloading, and regeneration of the human MTJ is scarce. Skeletal muscle has a pronounced healing capacity, but the connective tissue in contrast is associated with a long repair period and incomplete repair. The differences in tissue healing and regeneration may complicate MTJ repair after hamstring strain injuries and might be the underlying factor why these sports injuries have a high recurrence rate. Re-injuries might occur as the repaired tissues have inferior mechanical properties as it is often described when scar tissue forms following tissue damage. Prolonged inflammation has been tightly associated with scar formation in several tissues, and recent data on human strain injuries support the idea that inflammation is present for an extended time after strain injuries.

Many studies have evaluated factors associated with the athlete (intrinsic) and factors that are external to the athlete (extrinsic) for their relationship with hamstring injury. Over time these intrinsic and extrinsic factors have been examined across a large spectrum of athletic populations with varying degrees of rigour and consistency. Recently the value of much of the risk factor literature has been questioned, owing to several notable shortcomings: (1) the low quality of many studies, (2) the conflicting findings between studies, (3) the failure to recognise the interactions between risk factors, and (4) the dynamic nature of risk profiles within and between athletes. Increased chronological age and a history of previous hamstring strain are commonly, although not consistently, identified factors that place an athlete at a greater risk of hamstring strain. These non-modifiable risk factors (age and previous history) can potentially be mediated by improving eccentric hamstring strength and addressing muscle maladaptation to injury. Of the intrinsic risk factors that are ‘modifiable’, those related to the strength qualities and structural properties of the hamstrings have been shown to have a relationship with future injury. Extrinsic factors, particularly those related to match demands and training workloads, are also associated with hamstring injury and warrant consideration when managing athletes. This chapter has three key objectives: (1) present risk factors associated with future hamstring injury, (2) describe how factors interact or are impacted by other moderators to influence the risk profile of athletes, and (3) develop take-home messages regarding how to apply evidence about risk factors to practical situations and clinical decision-making in the real world.

Hamstring strain injury often results in neuromuscular performance deficits that persist beyond rehabilitation and the return to full training and competitive sport. It seems appropriate to address these deficits as a part of a sport-specific training program which primarily aims to enhance performance. Prolonged deficits in horizontal ground reaction forces in sprinting, repeat sprint performance, knee flexor eccentric strength and biceps femoris long head fascicle lengths have been observed in multiple studies of hamstring strain injury. Why such deficits persist beyond the return to sport is not known, although persistent neuromuscular inhibition of the injured muscles has been proposed. There is limited and mixed evidence for sprint running kinematic (technique) differences between previously injured and uninjured limbs or athletes, although more work in this area seems warranted. While there is some uncertainty about the optimal mix of methods for addressing the aforementioned deficits, sport-specific running programs in conjunction with continued monitoring of acceleration phase sprint performance and repeated sprint ability seem appropriate. Heavy strength training with at least some eccentrically biased exercises is also recommended to address deficits in eccentric strength and muscle fascicle lengths.