Introduction and background The plantaris muscle originates from the side of the femoral condyle medial and superior to the origin of the gastrocnemius lateral head, crossing latero medial the popliteal fossa.¹ This origin can have three variants: 56.5% without contact with neighbouring structures, 30.4% different interdigitating with the head of lateral gastrocnemius (19.6%) and a fibrotic extension to the patella (10.9%) and absent in 13%.² Muscle belly measures 7–13 cm³ and has a cross section between 3 to 7 mm where runs 5.5 cm tendon^{1 4} of 25–35 cm ranging between 1.5 and 5 mm⁵ and runs medially near the tibia between soleus and the medial gastrocnemius until nserted into the medial part of the Achilles tendon between 2–7 cm proximal to the calcaneal ⁶, the tendon is three times higher in the proximal part, while the total length obtained an average of 43.25 cm with a thickness variatons of 1.3 cm in myotendinous junction, 3.8 cm in belly muscle and 0.3 cm in the distal insert.¹ Cohen in 2009 ⁷ reflected four patterns of different insertion: type I (47%), a fan-shaped expansion on insertion into the medial edge of the tuberosity of the superior calcaneus on the Achilles tendon insertion; type II (36.5%) insertion into the calcaneus of 0.5 to 2.5 cm in the medial edge of the Achilles tendon; type III (12.5%), a large insertion involves the Achilles tendon; and type IV (4%), an insertion in the medial edge of the Achilles tendon of 1 to 16 cm proximal to the insertion of the Achilles tendon in the calcaneus. Because of its route performs the function of plantar flexor and foot inversion, and closed kinetic chain contributes to knee flexion.⁸ The plantaris receives innervation of tibial nerve from branches of L5 -S2 lumbosacral plexus. ⁸

Relationship into plantaris muscle and achilles tendinopathy Lintz et al. 2011⁹ in a cadaver study directly related plantaris tendon as a possible direct causes to generate Achilles tendon pathology. They concluded that the cross section of plantaris is 6.3 mm² and Achilles tendon 14.3 mm² in addition to being stronger and more rigid (7.7N) and less extensible (2.2 mm elongation) that the Achilles tendon (2.8 n and 2.8 mm) suggesting a difference in movement between the two structures under load. This difference of forces in the slip also shown in cases of rupture of the Achilles tendon, leaving intact plantaris. The plantaris muscle may predispose to inflammatory processes in the Achilles tendon.⁹ In 2011 Van Sterkenburg et al.¹⁰ analyzed 107 dissected legs and found several insertions plantaris: in 11 was inserted into the Achilles tendon, in 3 plantaris tendon and Achilles were together in the retinaculum, in 3 was inserted into the middle portion of Achilles tendon to the calcaneus proximal 2–6‘5 cm² was inserted into the deep fascia, in 2 anteromedial and in one was inserted on the front of the Achilles tendon fibres but inserted into the calcaneus. Macroscopic image retinaculum suggests a pathological pronation and suggested that the cause of the pain was due to the rich innervation of the paratendon. Alfredson et al. in 2014,¹¹ removed the plantaris muscle and made ? A scraping Achilles tendon to 17 patients with Achilles tendinitis and plantaris tendon inserted into the middle portion, as is the insertion in all literature is termed as generating possible cause of pathology. This study is tendinosis changes were found in the plantaris tendon and after treatment in all patients good results were obtained. Despite all hypothesis, the most influential seems to be generated by Spang et al. 2015,¹¹ In this recent study found that fat peritendiosa of connective tissue between the plantaris and the Achilles tendon is richly innervated in patients with Achilles tendinopathy in the middle third.

Relationship into plantaris muscle and fasciosis No studies have been found which directly link the presence of plantaris as a cause of plantar fasciosis. The hypothesis would be that generated by aquileo – calcaneus – plantar system could present the cause, comprising the Achilles tendon, the posterior part of the calcaneus and trabecular system, the plantar aponeurosis, and the intrinsic muscles of the foot.Shaw et al. (2008)¹² and Snow et al. (1995)¹³ demonstrated the continuity between the fibres of the Achilles tendon and plantar fascia; however, this continuity was only evident in the fetus and gradually decreased with age until adulthood, leaving only periosteum between the tendon and plantar fascia.In 2013 Stecco et al.,¹⁴ Bolivar et al.¹⁵ and Monteagudo et al.¹⁶ agree that there is no connexion between the Achilles tendon and plantar fascia, and showed that the only connexion is between the paratenon and plantar fascia. These studies associate excess tension in the hamstrings and leg with fasciosis. It also seems that the fasciotomy of the medial head of the gastrocnemius is an effective method for chronic plantar fasciosis. However, researchers suggest that reduced ankle dorsiflexion is, at least partially responsible for fasciosis, and not to the existence of the system of Achilles – calcaneus -plantar.Despite ruling out the system, Bolivar et al.,¹⁵ in their study they conducted a stretch with ankle dorsiflexion and knee extension in 100 subjects with fasciosis, and concluded that the pressure in the posterior calf is related to the appearance of the disease in the plantar fascia. Therefore, despite the absence of a anatomical connexion but found a functional connexion between the structures apparent, the authors believe that the lack of evidence in the anatomical literature, can rule out any system of Achilles- calcaneus–plantar.⁵ The unique relation that we find as a possible cause would be the innervation of the two structures, which no author comments, and a problem in foot biomechanics.

Relationship into plantaris muscle and tennis leg As only study, but without mentioning the possible reaction to reduce injury, found in 2006 Armfield et al.¹⁷ in which a study was performed using ultrasound to 141 subjects with a tennis leg. In 67% of cases was observed the rupture of medial gastrocnemius, in 21% was observed only a separation between the fascias of medial gastrocnemius and soleus but no tear was perceived, and 1.4% tendon rupture was associated the plantaris.

Study aims Based on the hypothesis generated above, the main goal of this study is to evaluate and analyse if the presence of a muscle belly plantaris with a cross section and grown up thickness is correlated with Achilles tendinitis and/or fasciosis in athletes.

Study design Cross-sectional study with repeated measures, the first group should have plantaris hypertrophied in the sonographic control. The other group have plantaris standard or absent. Each group will consist of the same number of participants.

Subjects and population A universe of subjects male population between 18 and 28 years old who meet the criteria for inclusion and exclusion. The number of participants that need to be part of the study sample is calculated with a total volume of subjects 100 participants (50 per group), although a previous pilot study will be conducted when it reaches the volume of 20 subjects (10 per group), to develop a pilot study in order to analyse the behaviour of the variables, in addition to approximate a standard measure of CSA and thickness plantaris muscle belly in order to draw conclusions when this is hypertrophied or normal.

Inclusion criteria Accept informed consent, healthy men athletes, Age between 18–28 years, Failure to comply with any exclusion criteria.

Exclusion criteria Decreased ankle dorsiflexion, Present a foot hyperpronation, Flatfoot, or cavus marked, Achilles Tendinopathy and/or fasciosis now or in the past 6 months, Injection of corticosteroids plantar fascia or Achilles tendon in the last year, History clinic with a history of rheumatic, tumour, degenerative neurological and/or severe injury of lower limb, Present inflammatory and/or infectious processes: bursitis, infections and skin problems, Present at the extremity radicular syndrome, Present calcifications and/or rashes, bone oedema and/or bone calluses on the joint, History of hip joint surgery, knee or ankle and foot, Uncooperative patients that may hinder the study, Pain in the tip with ideopathic’s origin or other causes not identified myofascial such as: neuropathies, lumbar canal stenosis.

Randomization and equalisation Participants meeting the inclusion criteria will be eligibled to participate in the study and may be part of the research sample. The simple will be divided non-randomly into two groups named above, with 50 subjects each group, this number is due to the statistical power and pilot control. The assignment of subjects in each group will be made depending on the cross section of the plantaris muscle belly.

Anthropometric variables The anthropometric data collection will take place following the guidelines Cineantropometría International Group (ISAK)¹⁸ Age: Continuous quantitative. Gender: categorical nominal. Weight: continuous quantitative. This parameter is assessed with the subject barefoot and in his underwear, a digital scale is used. Size: Continuous quantitative. For this parameter the distance shall be measured from the vertex to the soles of the feet with the participant standing in anatomical position and the occipital region, back, buttocks and heels in contact with the wall. The participant will make a deep breath at the time of measurement keeping your head in the Frankfort plane. a stadiometer be used. Body mass index: Quantitative continues. BMI=weight/height 2: For this parameter Quetelet index is used. Physical activity level: Discrete Quantitative: This parameter will be assessed by the IPAQ questionnaire: Short version – format self-administered last 7 days, translated into Spanish. Classifies adult populations depending on activity levels (low, moderate and high).¹⁹ Degree of disability Achilles tendon: Quantitative Variable discreet. An index of the severity of Achilles tendinopathy: this parameter for the VISA -A questionnaire will be used. This will happen at baseline, and accept a total value of <30%.²⁰  Plantar muscle cross section (CSA), at rest and contraction: Quantitative Variable discreet. Participating in prone position, knee and foot extension off the table. For this procedure an ultrasound machine ESAOTE Gamma, LINEAR PROBE SL1543 will be used, with it through which you can perform a scan on a cross section of the cross section of plantaris muscle comparatively. Reference is employed 3 cm proximal to the distal myotendinous Union (UMT), assessed for contraction by plantarflexion and inversion foot in open kinetic chain. Plantaris muscle thickness at rest and contraction: Quantitative Variable discreet. Participating in prone position, knee and foot extension off the table. For this procedure an ultrasound machine ESAOTE Gamma, LINEAR PROBE SL1543 will be used, with it you can perform a scan on a longitudinal section of the plantaris muscle thickness comparatively. Reference is employed 3 cm proximal to the distal myotendinous Union (UMT), assessed for contraction by plantarflexion and inversion foot in open kinetic chain. State Achilles tendon: Quantitative Variable discreet. Participating in prone position, knee and foot extension off the table. For this procedure an ultrasound machine ESAOTE Gamma, LINEAR PROBE SL1543 will be used, with it a longitudinal cut will be make in the order run an exploration of the Achilles tendon comparatively also allow you to determine the hypoechoic area and neovascularization using the colour doppler, in order to obtain additional information on the interaction of the tendon.²¹ Thickening of the plantar fascia: Quantitative Variable discreet. Participating in prone position, knee flexion 20° using a ‘foam’ in the foot. For this procedure an ultrasound machine ESAOTE Gamma, LINEAR PROBE SL1543 will be used, with it we will do an oblique medial longitudinal section and perform a scan of the insertion of the plantar fascia at the calcaneal tuberosity. Patient satisfaction: To evaluate this parameter the Spanish version of the scale Medrisk Instrument for Measuring Patient Satisfaction With Care Physical Therapy (MRPs) will be used. This scale consists of 20 items to assess patient 1 (very disagree) to 5 (strongly agree). This questionnaire is intended to assess comprehensively the satisfaction of the subjects during the study, making the questionnaire study completion.²² Workplan: Duration 30 months- Subjects Group A: Whose plantaris muscle have a CSA and thickness increase. – Subjects Group B: Whose plantaris muscle is standard or absent. In the first assessment every athlete will be assessed bilaterally by ultrasound. The measures we want to get is: CSA and plantaris thickness, thickness and state Achilles tendon between insertion 2–5 cm, thickness of the plantar fascia. Once the data is recorded, each athlete will be summoned every three months for 24 months for ultrasound check of the parameters mentioned and see if there are changes.The athlete should contact us if he appreciates discomfort and Achilles tendon, plantar fascia or suffering a leg tennis.

Results It is needed to finish the study to obtain results.

Conclusions If the results of the study confirm the hypothesis, many chronic Achilles tendinopathy and fasciosis should be reevaluated. In fact, it should studied future conservative treatments of plantaris as a treatment for these two diseases. In addition incorporate ltrasound as a measure of control and prophylaxis for professional players. If found a conservative approach to the plantaris could reduce the number of fasciotomies in chronic cases, and reduce recovery times and healthcare costs.