Muscle healing and the role of early eccentric muscle contractions

Muscle injuries are common in football practice. Lower limb muscle injuries represent around 37% of the total injuries in a football team being the hamstrings, adductors, quadriceps and calf muscles the most frequently injured muscles (Ekstrand J., Hagglund M., Walden M., 2011; Hagglund M., Walden M., Ekstrand J., 2005; Hawkins R.D., Hulse M.A., Wilkinson C., Hodson A., Gibson M., 2001; Hagglund M., Walden M., Ekstrand J., 2012). A muscle injury rehabilitation in football or any other sport should be as functional as possible and include early forms of recruitment of the injured muscle. The aim of the present article is to show the benefits of introduction of early isotonic contractions with focus on the eccentric phase instead of isometric muscle actions, and discuss which timings during the rehabilitation are appropriated for different types of stimulus to the injured muscle, after a moderate (grade 2) muscle injury.

How does a muscle heal?

After a muscle injury the damaged tissue follows a natural course of healing (Figure 1). First a destruction period takes place, with concomitant rupture and necrosis of the myofibres, formation of a haematoma, and an inflammatory cell reaction (Figure 2AB) (Huard, J., Li, Y., Fu, F.H., 2002; Hurme, T., Kalimo, H., Lehto, M., Jarvinen, M., 1991; Jarvinen, T.A.H., Jarvinen, T.L.N., Kaariainen, M., Aarimaa, V., Kalimo, H., Jarvinen, M., 2005; Kalimo, H., Rantanen, J. Jarvinen, M., 1997; Jar vinen, T.A.H., Jarvinen, M., Kalimo, H., 2013).

tissue repair phases and timescale

After this period starts simultaneously a reparative process where macrophages remove by phagocytosis the necrotized tissue, and the regenerative process of the myofibers with concomitant production of a connective tissue scar, alongside with capillary ingrowth into the injured area

(Bisciotti, G.N., Eirale, C., 2013; Jarvinen, T.A.H., Jarvinen, T.L.N., Kaariainen, M., Aarimaa, V., Kalimo, H., Jarvinen, M., 2005; Jarvinen, T.A.H., Jarvinen, T.L.N, Kaariainen, M., Aarimaa, V., Vaittinen, S., Kalimo, H., et al., 2007; Jarvinen, T.A.H., Jarvinen, M., Kalimo, H., 2013).

Macrophages also secrete growth factors activating the stem cells of the muscle tissue existent between the sarcolemma and the basal lamina of the myofibres, which will then sequentially form myoblasts, fuse into myotubes and mature into myofibres (Figure 2CDE) (Bisciotti, G.N., Eir ale, C., 2013; Jarvinen, T.A.H., Jarvinen, T.L.N, Kaariainen, M., Aarimaa, V., Vaittinen, S., Kalimo, H., et al., 2007; Jarvinen, T.A.H., Jarvinen, M., Kalimo, H., 2013).

The last stage of a muscle healing is the remodelling phase, which despite overlapping with the reparative and regenerative processes that last up to the third or fourth weeks after injury, remodelling can extend itself up to four or six months (Arrington, E.D., Miller, M.D., 1995; Tidball, J.G., 2005; Kalimo, H., Rantanen, J., Jarvinen, M., 1997). This stage is characterized by the maturation of the fibers recently repaired, and the re-organization of the scar tissue (Figure 2F) (Bisciotti, G.N., Eirale, C., 2013; Jarvinen, T.A.H., Jarvinen, M., Kalimo, H., 2013). Knowledge of this healing sequence and general aspects of each process is fundamental for rehabilitation´s strategies we implement at Football Medicine.

regeneration of a muscle injury 

  

How does the tensile strength of the injured area progresses through the course of healing?

Before answering this question it is relevant to understand when does actually new tissue is being formed, because hypothetically the injured area will be capable of sustaining some level of tension after fulfilled with some scar tissue. As stated in the section above, the first stage after the traumatic event is mainly characterized by a destruction and re-organization of the injured area. New tissue will hardly be formed in the first day after the injury. As it was shown in a study by Best et al. (2001), in which a stretch injury was induced to the tibialis anterior muscle of rabbits, focal fibrotic tissue constituted by deposits of collagen I and III were only noticeable after three days of the initial injury and were significant present after seven days.

The healing progression and its histological changes might be directly related with the capability of the tissue to deform to stimulus in terms of changes in its length but also the amount of load it can be absorbed by the muscle, which ultimately will determine the rehabilitation protocol. Considering this, it is interesting to verify that a study carried out by Corr et al. (2003) using the same laboratorial injury method in rabbits from Best et al. (2001), in which elongation to failure was analysed, concluded that the muscle compliance return to non-injured values after seven days from the injury date.

It will only be after ten to fourteen days of the injury that the healing scar presents some consistency, and this region will become no longer the weakest point of the healing area when subject to tensile forces. Around the scar tissue new mini muscle tendon junctions will be formed and become at this point the weakest region in the healing area in what concerns tensile resistance (Kaariainen, M., Kaariainen, J., Jarvinen,T.L.N, Sievanen, H., Kalimo, H., Jarvinen, M., 1998; Kaariainen, M., Jarvinen, T., Jarvinen, M., Rantanen, J., Kalimo, H., 2000).

As shown in previous studies, changes in the healing of the injured muscle are present through radiologic examination, using either ultrasound or Magnetic Resonance Imaging (MRI), with noticeable changes throughout time (Figure 3) (Connel DA, Schneider-Kolsky ME, Hoving JL, Malara F, Buchbinder R, Koulouris G, Burke F, Bass C, 2004 ). However, despite imaging such as MRI and ultrasound have been used to establish return to play prognosis after muscle injuries, (Peterson J, Thorborg K, Nielsen MB, Skjodt T, Bolvig L, Bang N, Holmich P, 2013; Moen MH, Reurink G, Weir A, Tol JL, Maas M, Goudswaard J, 2014; Kassarjan, A., Rodrigo, R.M., Santisteban, J.M., 2012), a recent review from Reurink et al. (2015) suggests no strong evidence for any MRI findings at baseline and return to play time to establish return to play time in hamstring injuries. A correlation between imaging features changes throughout time and the functional performance of the muscle is yet to be determined, as well features on the MRI after return to play and potential re injury risk. As it was observed in a study by Reurink et al. (2014), even when players are clinically recovered and cleared to return to play following hamstring injury, MRI changes are still present, and any risk of recurrence associated with them is still unknown. Therefore imaging should not be the main marker for rehabilitation progression.

How does the tensile strength of the injured area progresses through the course of healing?

Before answering this question it is relevant to understand when does actually new tissue is being formed, because hypothetically the injured area will be capable of sustaining some level of tension after fulfilled with some scar tissue. As stated in the section above, the first stage after the traumatic event is mainly characterized by a destruction and re-organization of the injured area. New tissue will hardly be formed in the first day after the injury. As it was shown in a study by Best et al. (2001), in which a stretch injury was induced to the tibialis anterior muscle of rabbits, focal fibrotic tissue constituted by deposits of collagen I and III were only noticeable after three days of the initial injury and were significant present after seven days.

The healing progression and its histological changes might be directly related with the capability of the tissue to deform to stimulus in terms of changes in its length but also the amount of load it can be absorbed by the muscle, which ultimately will determine the rehabilitation protocol. Considering this, it is interesting to verify that a study carried out by Corr et al. (2003) using the same laboratorial injury method in rabbits from Best et al. (2001), in which elongation to failure was analysed, concluded that the muscle compliance return to non-injured values after seven days from the injury date.

It will only be after ten to fourteen days of the injury that the healing scar presents some consistency, and this region will become no longer the weakest point of the healing area when subject to tensile forces. Around the scar tissue new mini muscle tendon junctions will be formed and become at this point the weakest region in the healing area in what concerns tensile resistance (Kaariainen, M., Kaariainen, J., Jarvinen,T.L.N, Sievanen, H., Kalimo, H., Jarvinen, M., 1998; Kaariainen, M., Jarvinen, T., Jarvinen, M., Rantanen, J., Kalimo, H., 2000).

As shown in previous studies, changes in the healing of the injured muscle are present through radiologic examination, using either ultrasound or Magnetic Resonance Imaging (MRI), with noticeable changes throughout time (Figure 3) (Connel DA, Schneider-Kolsky ME, Hoving JL, Malara F, Buchbinder R, Koulouris G, Burke F, Bass C, 2004 ). However, despite imaging such as MRI and ultrasound have been used to establish return to play prognosis after muscle injuries, (Peterson J, Thorborg K, Nielsen MB, Skjodt T, Bolvig L, Bang N, Holmich P, 2013; Moen MH, Reurink G, Weir A, Tol JL, Maas M, Goudswaard J, 2014; Kassarjan, A., Rodrigo, R.M., Santisteban, J.M., 2012), a recent review from Reurink et al. (2015) suggests no strong evidence for any MRI findings at baseline and return to play time to establish return to play time in hamstring injuries. A correlation between imaging features changes throughout time and the functional performance of the muscle is yet to be determined, as well features on the MRI after return to play and potential re injury risk. As it was observed in a study by Reurink et al. (2014), even when players are clinically recovered and cleared to return to play following hamstring injury, MRI changes are still present, and any risk of recurrence associated with them is still unknown. Therefore imaging should not be the main marker for rehabilitation progression.

Early stage of rehabilitation

After the injury episode an immediate protective phase should take place in the first few days (until day 5-6 after injury). Rest is fundamental, especially in the activities where pain is present along with the injured muscle recruitment, and it will contribute to prevent excessive scar formation. There seems to be a positive association between active mobilization immediately after injury and recurrence of the injuries in the original site, reinforcing the need for this protection phase (Jarvinen M., Lehto M.U., 1993). Nevertheless this remark, early pain free active mobilization after a few days, when the proliferative stage of the healing process begins, will induce capillary ingrowth into the injured area, better regeneration of the muscle fibers and more parallel orientation of the regenerating myofibers, improving the rehabilitation outcomes (Jarvinen,T.A.H., Jarvinen, T.L.N., Kaariainen, M., Kalimo, H., Jarvinen, M., 2005).