Author - Tim Janssen Rehabilitation Physiotherapist - Feyenoord Rotterdam

In the rehabilitation of lower-leg injuries, there appears to be a missing link in the progression from tissue healing to return to play. This gap may help explain the high rates of injury recurrence and the frequent decline in performance observed once athletes resume full training and competition (1, 2).

During rehabilitation, practitioners often prioritise rebuilding muscle and tendon capacity through traditional isotonic strength exercises, such as calf raises. While these exercises play an important role in restoring tissue capacity, they often fail to address the primary underlying deficit associated with the cause of many lower-leg injuries.

The Problem: Insufficient Braking Ability

The missing factor across the “Big Three” lower-leg injuries - Achilles tendinopathy, ankle sprains, and medial tibial stress syndrome (shin splints) - is a systematic and progressive development of impact absorption, or more precisely, braking ability. 

Athletes may regain strength and tolerate loading in controlled environments, yet still lack the ability to effectively decelerate the forces during foot-plant in dynamic, sport-specific movement. This deficiency leaves the system vulnerable at the moment of impact.

The Underlying Cause - Why is braking such a critical yet overlooked skill?

Conventional rehabilitation models tend to emphasise isotonic exercises aimed at rebuilding tissue capacity (a primarily quantitative approach - think elastic bands, calf raises, and machines) (4), before transitioning rapidly - both literally and figuratively - into plyometric exercises for power development and return to play.

However, lengthening and shortening muscle fibres against resistance does not necessarily reflect lower-leg musculature behaviour during real movement.

Research demonstrates that the two primary plantarflexors - the soleus and gastrocnemius - serve distinct and highly specialised roles during high-performance tasks such as maximal acceleration sprinting (3). These roles arise from key anatomical differences that fundamentally alter how each muscle contributes to movement.

During the first half of stance, the soleus produces substantial braking forces. It accounts for a large proportion of the vertical impulse at foot contact and functions primarily as a supporter of the system. In contrast, the gastrocnemius contributes more significantly to forward propulsion, particularly during acceleration (3).

Rather than simply increasing strength through repetitive lengthening–shortening exercises, rehabilitation stimuli should reflect the supporting role of the soleus and the propulsive role of the gastrocnemius.

Several anatomical characteristics of the calf musculature support and highlight why traditional isotonic exercises fail to adequately mirror their function in contextual movement.

1 - Pennate structure

Both the soleus and gastrocnemius are pennate muscles, meaning their fibres are angled relative to the line of pull. As a result, shortening of the contractile elements (myofibrils via actin–myosin cross-bridging) leads to a disproportionately small change in ankle joint angle. In other words, large changes in muscle length do not automatically translate to large joint movements.

2 - Short, steep force–length relationship

Both muscles operate on short, steep force–length curves. They can resist high forces only within a narrow optimal length range. Deviations beyond this range - either longer or shorter - result in a rapid decline in force capacity.

3 - Bi-articular function

The gastrocnemius crosses both the knee and ankle joints, enabling it to transfer forces across joints within the kinetic chain. As the knee extends, the gastrocnemius risks being lengthened eccentrically beyond its optimal force-producing length. To compensate, it shortens by pulling on the Achilles tendon and plantarflexing the ankle, thereby contributing to forward propulsion during acceleration.

4 - Abundance of passive tissue

Both muscles contain substantial passive connective tissue. This suggests their primary role may be more elastic than concentric (shortening of muscle). During co-contraction, the muscle bellies expand laterally, tensioning passive tissues longitudinally. These tissues then transmit force up and down the chain to the ankle, contributing to propulsion without large changes in muscle length.

Taken together, these characteristics indicate that the calf muscles are optimally designed to function isometrically as stabilisers during stance, and elastically as force transmitters during propulsion.

This makes the ability to resist and control forces during impact absorption essential before progressing to plyometric loading. Without sufficient braking capacity, the calf musculature may be forced beyond its optimal operating range during dynamic tasks, increasing the risk of tissue overload and injury.

 

The Solution - Building Better Brakes With Perturbation

“Lower-leg injuries persist not because we fail to heal tissue, but because we fail to restore the system’s ability to decelerate impact forces (stiffness).” 

To prepare athletes for plyometrics and return to play, while respecting the true function of the calf muscles, rehabilitation must include a dedicated phase focused on braking and force absorption with perturbation.

When athletes only progress to plyometric exercises after demonstrating mastery of braking, they are better prepared for the true culprit behind both acute and chronic lower-limb injuries.

Training braking under perturbation (random, variable disturbances introduced caused by an external influence) further enhances the system’s capacity to organise the body and manage forces during impact.

Perturbation (for example the sloshing of water in the Hydrovest 2.0) during braking exercises improves the body's ability to both share the forces evenly across joints through co-variation (rather than concentrate external forces in vulnerable "hot-spots" which could incur injury), and ensure these forces contribute positively to push-off during stance.

Solution Mechanism – How To Build The Brakes

It is important to recognise the phase transition between acceleration and high-speed running. The mechanical demands placed on the lower-leg musculature differ substantially between these phases.

Accordingly, rehabilitation interventions must be tailored to these distinct demands.

During acceleration-focused tasks, the upper body (UB) should be positioned over the forefoot (FF) with a low centre of mass (COM). This configuration closely reflects acceleration biomechanics and influences not only force magnitude, but also force vector orientation and the joint torques the calf muscles must resist.

In contrast, high-speed preparation exercises require a higher COM that is aligned with, or slightly behind, the base of support (BOS).

Progression within this framework should be guided by:

1. High standards for ankle stiffness quality, prioritising braking before rebound.

2. The ability to brake effectively in three-dimensions, under perturbation (an unexpected deviation of the system from it's regular state caused by an outside influence - such as the shifting of water in the Tidal Tank PRO) .

3. Objective measures such as ground reaction force (GRF) and impulse metrics derived from Force Plate systems during return-to-play (RTP) decision-making.

A Practical Framework – Application in the Field

We propose a Three-Tier Rate of Force Development (RFD) Framework for the braking phase of lower-limb injury rehabilitation.

TIER 1 – LOW

Early sub-phase | Red light | Low-impact exercises

This phase introduces the concept of “catching” the body with the foot, using the ankle as a strong anchor point. The external load or effective force (expressed as kilograms or multiples of bodyweight [BW]) is typically below the athlete’s bodyweight.

Tier 1 - Exercise 1 (Acceleration)

 

Tier 1 - Exercise 2 (Top-Speed)

TIER 2 – MEDIUM

Intermediate sub-phase | Amber light | Medium-impact exercises

This tier progresses from low-impact work by increasing the height or velocity from which the athlete must absorb their bodyweight. Perturbations are introduced across all three planes of motion.

Tier 2 - Exercise 1 (Acceleration)

Tier 2 - Exercise 2 (Top-Speed)

 

TIER 3 – HIGH 

Advanced sub-phase | Green light | High-impact exercises

At this stage, the training wheels come off. The athlete is exposed to braking forces that can reach up to eight times bodyweight, levels comparable to sprinting, cutting, and landing. Performance here determines readiness for plyometrics and return to running (RTR).

Tier 3 - Exercise 1 (Acceleration)

Tier 3 - Exercise 2 (Top-Speed)

About The Author - Tim Janssen

Tim Janssen is a sports physiotherapist specialising in injury rehabilitation through a dynamic systems approach. He currently works within the Feyenoord first-team medical staff, where he is responsible for player injury rehabilitation. Alongside his club role, Tim works privately with patients on a one-to-one basis and lectures at physiotherapy workshops across the Netherlands.

 

References 

1. Silbernagel KG, Crossley KM.
   A proposed return-to-sport program for patients with midportion Achilles tendinopathy.
   J Orthop Sports Phys Ther. 2015
   
   
2. Ardern CL, Glasgow P, Schneiders A, et al.
   2016 Consensus statement on return to sport from injury.
   Br J Sports Med. 2016
   
   
3. Pandy MG, Lai AKM, Schache AG, Lin YC.
   How muscles maximize performance in accelerated sprinting.
   Scand J Med Sci Sports. 2021.
   
   
4. Bohm S, Mersmann F, Arampatzis A.
   Human tendon adaptation in response to mechanical loading: a systematic review and meta-analysis.
   Sports Med. 2015