Principles of Load Management in Sport and Exercise Rehabilitation

Original Editor - Wanda van Niekerk based on the course by Lee Herrington

Top Contributors - Wanda van Niekerk, Jess Bell, Kim Jackson, Lucinda hampton and Aminat Abolade  

Model of Injury Causation

Several factors can predispose an athlete to injury. Some of these are non-modifiable predispositions (anatomy, genetics, previous injury, environmental factors) and some are modifiable predispositions. Modifiable predispositions can be long-term (training history, strength, movement, skill, flexibility) or short-term (state of the athlete, tired, mood, diet, etc.). No matter how predisposed an athlete is, they can only become injured when exposed to load. And there still needs to be an inciting event leading to the injury. This flow diagram by Dr Lee Herrington illustrates this point:

Model of Injury Causation

Read more here: Musculoskeletal Injury Risk Screening

Definition of Load

The International Olympic Committee defines load as follows:

“The sport and non-sport burden (single or multiple physiological, psychological or mechanical stressors) as a stimulus that is applied to a human biological system (including subcellular elements, a single cell, tissues, one or multiple organ systems, or the individual). Load can be applied to the individual human biological system over varying time periods (seconds, minutes, hours to days, weeks, months and years) and with varying magnitude (ie, duration, frequency and intensity).”

Characteristics of Load

• Load is an external stimulus applied to an individual athlete that is measured independently of their internal characteristics
• Exposure to load results in a physiological and psychological response
• Load can be applied to the whole system or whole body level or applied to the tissue level (system load vs tissue load)

In sports injury rehabilitation, load application is often focused on applying load to the specific tissue that we wish to influence. The following graphs explain the difference between system load and tissue load.

Graphic illustrating vertical ground reaction forces when walking and running on a system level and a tissue level

The graph on the left depicts the amount of body weight (x BW) the body is exposed to in terms of vertical ground reaction force when walking, running at a moderate pace for 10km, and running at a fast pace for 10km. The load (vertical ground reaction force) going through the whole body (system load) increases steadily as the pace is increased.

When converting the load through specific areas of the body as in the graph on the right, it is clear that even though gravity is the same, the load expressed at different joints changes noticeably with pace.

• At the hip, as speed increases, a consistent increase in load or moment is seen.
• At the knee, as speed increases, there is a huge increase in load when changing from walking to moderate pace running. However, there is a relatively small increase in load when changing from moderate to fast pace running. Thus, the knee responds differently to the hip to a change in running pace.
• At the ankle, the level of load is higher, regardless of whether the task is walking or running. Like the hip, there is a more consistent relationship to changes in pace. However, the load through the ankle starts at a much higher baseline.

From this example, it is clear that even though gravity is the same (so the vertical load is the same), the way that load is expressed at different joints changes with pace. This shows that both system load and tissue load need to be considered when applying load in rehabilitation.

Identifying Load

• External load = features of training load describing magnitude and amount of physical work
  • Examples of external loads which could be captured:
    • Training parameters such as time, distance, repetitions, nature of the load (absolute speeds, acceleration, deceleration, biomechanical moments)
    • In sport itself – impact, nature of the skill, competition and the weight lifted

• Internal load = features describing resultant physiological and biomechanical response to load
  • Examples of internal loads which could be captured:
    • Things the athlete feels or expresses such as:
      • Session Rate of Perceived Exertion (RPE)
      • Wellness parameters:
        • Mood, tiredness, sleep, readiness to train, soreness
      • Physiological parameters
        • Heart rate (recovery, variability, resting)
        • Blood tests and results

• Relationship between exposure (load) and consequence
  • There is not necessarily a clear relationship between load, the load exposure and the consequence of that load. The consequences of load exposure vary considerably depending on the individual athlete and their previous experience with load.

Is Load a Bad Thing?

Load Deformation Curve

Load deformation curve

• Shows tissue deformation when a load is applied
• Initially, when a biological structure is loaded, the tissue deforms slowly and then more rapidly until it reaches the point of micro failure
• If the load is removed before this point of micro failure (elastic region), the tissue will return to its previous form
• If the tissue is loaded beyond the elastic region, there is a permanent change in the tissue

Implications of the load-deformation curve in injury or exercise rehabilitation

• If the aim is to create tissue adaptation and load tolerance (i.e. stronger and able to resist load), training or rehabilitation need to happen within the left half of the micro failure zone. This will cause enough damage to stimulate physiological processes which will allow for tissue adaptation.
• If training and rehabilitation happen on the right half of the micro failure zone, too much damage occurs, which may lead to irreparable damage and breakdown.

Load is a good thing, but can also be a bad thing

• Correct loading is necessary for the rehabilitation and strengthening of an athlete, but if too much is applied, it can have negative consequences.
• The "sweet spot" for loading needs to be determined
• Too little load = failure to provide appropriate stimulus to the tissue to adapt and strengthen and can lead to atrophy
• Too much load = irreparable tissue breakdown

What About Repetitive Load?

• High load might be protective

• Sudden increases or changes in load might be the problem
  • When increases in load are ≥ 15% above the previous week’s load, injury risk escalates to between 21% - 49%
  • To minimise injury risk, weekly training load increases should be limited to < 10%
  • Read more: The training—injury prevention paradox: should athletes be training smarter and harder?

• Acute:chronic workload ratio (ACWR)
  • Acute:chronic workload ratio is the amount of training the athlete has completed during the period of rehabilitation compared with what is needed for a full training session.
  • Acute load is the training done in 1 week. Chronic load is the average acute load / training done in the last 4 weeks. The ratio between acute and chronic shows if the acute workload is greater or less than the total workload of the weeks before it.
    • An acute:chronic workload ratio of 0.5 means that the patient trained/completed half of what was prepared for during the 4 weeks prior
    • A ratio of 2.0 means the patient did twice as much. Anything more than 1.5 is seen as a spike in training and could be considered an injury risk.
  • Recently the ACWR has received criticism
    • Read more about the reasons why, here: The acute:chronic workload ratio. Science or religion?
  • Biological systems versus local tissue
    • One of the reasons why the ACWR has struggled to replicate itself across varied circumstances is that the measures quite often used to measure load, measure whole system load rather than tissue load and injury at a tissue level.
    • Load applied at the tissue level can be quite different than the load applied across the whole system.
    • Using different metrics when loading at tissue level compared to the metrics used to measure loading at a system level is therefore recommended.
    • A recent systematic review investigating the relationship between ACWR and injury risk in sports reported high variability in studies. However, studies were generally of good quality, completed in multiple countries and included various sports. It did appear that using ACWR for external and internal loads may be related to injury risk. However, there are still issues with the ACWR method and this should be addressed through further research.

Managing Rehabilitation Loads

• Collect data to base decisions on
• Understand external load and the extent of external loads
  • Level of external load can be measured through:
    • Body weight or multiples of body weight
    • Weight lifted
    • Global (system) level load can be calculated, but ideally, tissue level load should be understood

• Research to improve our understanding on how typical tasks load tissue is growing
  • Read more:
    • Knee joint loading in healthy adults during functional exercises: implications for rehabilitation guidelines
    • Exercise Progression to Incrementally Load the Achilles Tendon

• Repetitions (and sets) or distance covered
  • Consider the number of times the load is applied to the athlete
  • Also consider the non-rehabilitation or non-sports load in athletes
    • Work, activities of daily living (ADLs)
    • Understanding these other loads is crucial to understanding the totality of an individual’s load

• Monitor the consequences of loading
  • How does the tissue respond to load?
  • Ways to measure this: read more here
  • What is the global response to load?

Rehabilitation Process

Rehabilitation Process

• Assess the extent of the problem
• Understand the current status
• Remove any negative forces
• Progressively expose system and tissue to load
• Reach performance goals

• Clinicians need to understand:
  • The extent of the loads an athlete is exposed to
  • How does the athlete / tissue react to that load?
    • Development of pain
    • Development of stiffness
    • Development of soreness
  • Fatigue
    • Less able to repeat effort the next day

• This will indicate if an athlete is adapting appropriately to rehabilitation or training loads
• Using data to understand knowledge and then act upon it

Progression of Rehabilitation Loads

Example of Progressing Load for a Runner with Achilles Tendinopathy

The following example is from Lee Herrington's video on Principles of Load Management in Sport and Exercise Rehabilitation.

Available Data on Achilles Loading

• Peak loads during running of x5-6 BW (Body Weight)
• Trowell et al. peak loads
  • Ankle bounces < running
  • Bounding = running
  • A-skips > running
• Trowell et al. compared plantarflexor musculotendon unit (MTU) output between plyometric exercises and running. The results included:
  • "Ankle bounce produced low gastrocnemius and soleus MTU output compared to running."
  • "One A-skip generated greater total positive and negative work for both plantarflexors compared to one running stride and each A-skip cycle involved twice the number of ground contacts and toe-off phases as one running stride, thus increasing total work for the plantarflexors."
• The researchers concluded the following:
  • Ankle bounce and A-skip produced low MTU output for gastrocnemius and soleus compared to running. This may suggest that these two exercises can be used as alternatives to running if low plantarflexor loads are needed.
  • Bounding produced greater peak strain compared to running and may be used in runners who need to train or rehabilitate with high eccentric loads
  • Hurdle jumps may be used in runners who need soleus overload, with low lateral gastrocnemius loads.

• Baxter et al. peak loads
  • Seated heel raise x 0.5 BW
  • Single leg squat x 1 BW
  • Standing heel raise x 2 BW
  • Forward hop x 5 BW
  • Single leg drop jump x 5.5 BW

Table 1. Achilles tendon rehabilitation exercises and peak loading (BW)

Tier	Exercise	Loading Peak (BW)
Tier 1	Seated heel raise (2-leg)	0.5 ± 0.2
	Seated heel raise (1-leg)	0.7 ± 0.2
	Squat	1.1 ± 0.3
	Low step up (leading leg)	1.6 ± 0.4
	High step up (leading leg)	1.8 ± 0.3
	Standing heel raise	1.6 ± 0.2
Tier 2	Rebounding heel raise (2-leg)	2.5 ± 0.7
	Lunge (leading leg)	2.1 ± 0.6
	Low step down (leading leg)	2.2 ± 0.5
	Low step up (trailing leg)	2.9 ± 0.4
	High step down (trailing leg)	2.6 ± 0.3
	Walk (stance)	3.3 ± 0.3
	Low step down (trailing leg)	2.9 ± 0.3
	Forward jump (2-leg)	3.2 ± 1.0
	High step down (leading leg)	3.2 ±0.6
	High step up (trailing leg)	3.7 ± 0.6
	Lunge (trailing leg)	2.4 ± 0.5
	Counter movement jump (2-leg)	3.4 ±0.3
	Rebounding heel raise	4.2 ± 0.9
	Standing heel raise (1-leg)	3.0 ± 0.3
Tier 3	Drop jump (2-leg)	3.6 ± 0.6
	Hopping (2-leg)	4.8 ± 1.8
	Run (stance)	5.2 ± 0.9
	Forward hopping (2-leg)	5.2 ± 2.6
	Counter movement jump (1-leg)	4.9 ± 0.6
	Forward jump (1-leg)	5.4 ± 1.1
Tier 4	Hopping (1-leg)	6.7 ± 1.8
	Drop jump (1 -leg)	5.5 ± 0.8
	Lateral hopping (1-leg)	7.3 ± 2.4
	Forward hopping (1-leg)	7.3 ± 1.9

Requirements of the Patient for Running

• Typically runs 25 – 30 km per week (6 – 10 km each run), runs 3 -4x week
• Best 10 km time 48 minutes, trains at 5min/km pace
• Typical running cadence 170 steps/min
• Aerobic exercise target heart rate 120 beats/min
• Main reason for running:
  • Health (mental and physical)
  • Weight management

Baseline Data

• Pain after running greater than 2km post-run and the next morning
• Pain limits standing heel raise to 18 repetitions, but is able to do 28 on the other leg
• Able to bilateral ankle bounce 10 times with no pain

Managing and Progressing Tissue Load

Peak Load Exposure

• For Achilles tendon during running, data indicates 5-6BW
• Peak load exposure – progression
  • Continue with 2 km running
  • Build ability to tolerate load
    • Ankle bounces
    • Bounding
    • A-skips

Volume of Exposure

• Incrementally increase running volume / distance from 2 km
• Monitor the effect of this increase
  • Morning stiffness and soreness
  • Knee to wall test
  • Calf raises

Managing and Progressing System Load

Aerobic Fitness

• Provide an alternate stimulus if running is not enough, such as an exercise bike, or combine with the current run load tolerance of the athlete
• Training at heart rate (HR) of 120 beats/minute - aim to do bike workout at same intensity
• Still providing the athlete with weight management and mental health stimulus through different forms of exercise

Key Take Home Messages

1. Understand the performance requirements
2. Identify what load the tissue (and individual) can currently tolerate
3. Identify the gap between current status and performance requirements
4. Progressively apply the maximum loads the tissue (and individual) can tolerate towards overall performance requirements
5. Assess the impact of loading on the tissue and the individual