Introduction

The gastrocnemius and soleus muscles are important structures in locomotion as their tendons absorb peak forces during walking and running gait. With decreasing ankle dorsiflexion, peak forces that have to be absorbed by the calf muscles increase. This increased strain is thought to be a contributing factor to achilles tendinopathy as decreased ankle dorsiflexion is associated with a 2.5–3.6 times higher risk of Achilles tendinopathy. A common intervention used to improve ankle dorsiflexion is the use of eccentric exercises, as it is theorized that this may cause lengthening of the musculotendinous junction. This study aimed to determine whether eccentric exercises increase ankle dorsiflexion.

Methods

In this prospective study young healthy soccer players (aged 14-21) with decreased ankle dorsiflexion were included. A decreased ankle dorsiflexion was defined as ≤10cm toe-to-wall distance during the weight-bearing lunge test (WBLT), or soleus or gastrocnemius muscle flexibility ≤ 34°. Participants were recruited from the youth sections of 2 Dutch professional premier division soccer clubs.

The intervention group performed stretching and eccentric exercises for 12 weeks on top of their regular training regimen. All players of the intervention group were instructed to perform the eccentric exercises three times a week for 12 weeks. The workload was gradually increased by approximately 20% every week to prevent overloading, starting at two times four repetitions. The sets for eccentric calf muscle exercises were repeated twice in the first four weeks, with 4 repetitions in the first week, increasing with 2 repetitions per week. In week five to eleven, sets were repeated 3 times, starting with 7 repetitions, and increasing with one repetition per week. Three sets of 15 repeats were accomplished in week twelve. The stretching exercises were repeated three times for 30s for the at-risk leg. The control group only participated in their regular training 4 times per week for an average duration of 2h.

Results

So, do eccentric exercises increase ankle dorsiflexion? Mean ankle dorsiflexion improved from 7.1 (± 1.8) to 7.4 (± 2.4) cm (p = 0.381) in the intervention group. In the control group, mean dorsiflexion improved from 6.1 (± 2.1) to 8.2 (± 2.9) cm (p < 0.001). Dorsiflexion did thus only improve statistically in the control group who weren’t doing all the lengthening and strengthening.

Mean soleus muscle flexibility improved from 31.0° (± 1.7°) to 32.5° (± 3.3°) degrees (p = 0.075) in the intervention group, while a statistically significant improvement from 28.3° (± 3.4°) to 33.6° (± 4.7°) (p < 0.001) was found in the control group. The same finding can be seen with the change in gastrocnemius flexibility, where the control group achieved a statistically significant change in muscle flexibility from 28.3° (± 4.4°) to 31.2° (± 5.6°); (p = 0.004) while the intervention group had a non-significant change from 29.8° (± 3.0°) to 31.0° (± 3.5°); (p = 0.188).

So contrary to common belief, it appears that eccentric exercises combined with stretching do not improve ankle dorsiflexion. BANG…

Questions and thoughts

While the trial was well designed, some aspects should be borne in mind when looking at these results. The intervention and control groups were sampled from 2 different soccer clubs. Although the clubs continued their regular training regimen, the training routines may have differed a lot between both clubs. This variable was not controlled for when measurements were obtained. Another important factor to note is that the calf muscle flexibility measurements were gathered one week after the start of the soccer season for both teams. We all know that it is not uncommon to experience some muscle soreness and tightness at the start of a new season, and so the measurements taken at the end of the first training week could have easily been influenced by this. This study had a duration of 12 weeks, which may not have been enough to result in changes in tissue properties following lengthening exercises as it is hypothesized that changes occur at a sensory level at first and true tissue properties changes occur only on the long term.

Talk nerdy to me

The measurements obtained in this study showed excellent inter- and intrarater reliability. The change in dorsiflexion surpassed the minimal detectable change and thus reflected a true improvement in the control group. This was not true for the soleus and gastrocnemius muscle flexibility, where the changes stay within the measurement error and can therefore not be assigned as true change.

An important limitation of this study is that no sample size calculation was performed. Instead, the authors chose to include 100 healthy soccer players without questioning whether this would be enough to reach sufficient statistical power. When consulting the protocol for this study, it becomes clear that the change in ankle dorsiflexion was not the primary outcome measurement and other types of exercises may have been performed besides the eccentric and stretching exercises. This may imply that the observed change may not fully reflect the effect of the eccentric exercises and stretching alone like it was described in this article, and thus you should remain critical when interpreting these results.

Take home messages

A 12-week lengthening exercise program does not improve ankle dorsiflexion in young soccer players.

The 12-week duration may not have been sufficient to result in structural tissue changes.

12-week eccentric calf muscle exercises may not be preventive for Achilles tendon injuries.

Reference

Lagas, I. F., Meuffels, D. E., Visser, E., Groot, F. P., Reijman, M., Verhaar, J. A., & de Vos, R. J. (2021). Effects of eccentric exercises on improving ankle dorsiflexion in soccer players. BMC Musculoskeletal Disorders, 22(1), 485.