Sports Medicine

https://doi.org/10.1007/s40279-022-01641-y

CURRENT OPINION

Putting “Heavy” into Heavy Slow Resistance

Scot Morrison1,3   · Jill Cook2

Accepted: 2 January 2022

© The Author(s) 2022

Abstract
The body of literature on tendinopathy management has come a long way in the last few decades and a variety of changes in
the clinical approach have emerged from this research. One particular approach that shows promise has been called “heavy
slow resistance” (HSR), and this has been the subject of investigation in a number of randomized controlled trials. While
the premise for this approach is defensible, a critical examination of the implementation of these HSR protocols results in
some concerns when compared to basic exercise science principles. This article lays out some considerations that will help
future investigators to improve their exercise prescription approaches in this area.

placed on eccentric contractions does appear to be unneces-

Key Points  sary though, since similar outcomes are seen regardless of
contraction type, and so heavy slow resistance (HSR) has
Relative submaximal lifting capacity (RSLC) will dictate become an accepted approach for the early stages of man-
repetitions at a set load and slower tempos compound agement due, in part, to its ability to moderate the rate of
this effect. loading while still providing a sufficient load [1–5]. While
Heavy slow resistance (HSR) is commonly used when uncertainty surrounds the reason for these improvements
managing tendinopathies since tendon strain sufficient (e.g., adaptations in some or all of tendon, muscle, kinetic
for adaptation is generally more likely at a higher per- chain and/or brain), patient outcomes do support the use
centage (> 70%) of maximum, but the RSLC will limit of this intervention. However, there are some fundamental
total repetitions possible at that load (< 6). programming principles that appear to be missed in the HSR
literature that require clarification in order to make exercise
This means that volume must derive from something prescription match the idea contained in the title “HSR.”
other than increasing repetitions per set if %RM and
tempo are maintained.
2 Background

Targeted exercise prescription has a variety of parameters

1 Introduction that influence each other and can be manipulated to influ-
ence the desired outcomes. These include the rate of loading
The management of tendon pain via progressive load- (slope of the force/time curve), the intensity (load as % of
ing is well documented and appears to be one of the best maximum), the time under tension, the rest between sets, the
interventions currently available. The traditional emphasis individual’s perceived effort, the joint positions and muscle
lengths during loading, and the volume-load (load x sets x
repetitions) performed. Of these, the exercise intensity and
* Scot Morrison rate of loading are two of the most important parameters pre-
scot@physiopraxis.co
scribed to address tendon issues. While this paper focuses on
1
Physio Praxis PLLC, Vancouver, WA, USA HSR training, sports with significant elastic energy storage
2 demands require rehabilitation that address these demands,
Musculoskeletal Research Centre at La Trobe University,
Melbourne, Australia and while it is traditionally addressed after a HSR program,
3 some concurrent work could be indicated.
Department of Neuroscience, Biomedicine and Movement
Sciences, University of Verona, Verona, Italy

Vol.:(0123456789)
 S. Morrison, J. Cook

To create change in the mechanical properties of the ten- managing 9.67 (± 0.91) repetitions compared with untrained
don, stress must be applied to the tendon at a magnitude people (7.14 ± 0.74) when tested at 85% of 1RM in the back
that causes sufficient strain [6]. Practically speaking, a load- squat [11]. This is important to consider in tendon condi-
ing approach at higher intensities, defined by percentage of tions, as some tendinopathies occur in highly trained people
one repetition maximum [1RM, the maximum weight that (e.g., patellar tendinopathy), while others can occur in more
can be lifted once (%RM)], is generally an acceptable proxy sedentary populations (e.g., gluteal tendinopathy).
for this. For example, a systematic review by Bohm et al. In addition, the relationship of the RSLC to the 1RM
found the intensity threshold likely to ensure adaptations in varies across time in individuals. Braith et al. investigated
mechanical, material, and possibly morphological proper- 1RM and 7–10RM in a training group over time, and found
ties of tendon was 70% of maximum, and this seems to be that the % of RM increased more for the 7–10RM test than
true regardless of contraction type [7, 8]. It is important the max did [12]. The 7–10 repetition range increased by
to remember that this 70% RM is a general estimate of a more than 10% (pre-training 68.4% ± 7.2 of RM baseline,
continuous variable whose true value will vary based on post-training 79.1% ± 7.0 of RM). While the predictive abil-
the individual’s muscular strength relative to the stiffness ity of this 7–10RM test for 1RM was good (± 10%), it over-
of their tendons. This is evidenced by findings like those estimated the RM in trained individuals, which suggests a
of Quinlan et al., reporting tendon changes at a lower load more accurate estimating procedure that is based on training
(60% RM), and others reporting upwards of 90% of RM state may need to be developed. It can be concluded then that
being necessary to see sufficient strain [6, 9]. Because of fluctuations in RSLC based on training type and status will
this, in a clinical setting it may be better to view prescrip- influence the actual %RM intensity used even if repetition
tions based on loads of > 70% as a “good starting bet” to ranges are similar. Despite this variability, if 12 repetitions
increase the probability of achieving the necessary tendon or more can be completed with a given load it is highly likely
strain for adaptation. that this load will be less than the 70% RM intensity goal of
In a high-performance setting a 1RM can be determined tendon loading.
by lifting progressively heavier loads until a one-rep-max is Of course, these studies have all involved uninjured indi-
reached, but clinically this may be contraindicated. Alterna- viduals, and in a patient population the length of tendon
tively, a 1RM can be estimated by assessing a submaximal symptoms and the resulting dysfunction may influence the
load taken to the point where another repetition is not pos- relative intensity as well. Tendon pain typically results in
sible (i.e., performing a 3RM or a 5RM to calculate a 1RM). a person unloading the affected area during tasks, which
The accuracy of the calculated 1RM is inversely related means most multi-joint and bilateral exercises find the indi-
to the number of reps achieved. Therefore, the load lifted vidual using a movement strategy that decreases the load
should be low enough to hit at least two to three repetitions, on the affected tendon while still accomplishing the task.
but failure occurring at or before eight repetitions is likely This ability to offload the tendon can be controlled through
best. All testing should be done after a warm-up of progres- the use of isolated exercises, as all movement solutions that
sively heavier loads with sufficient rest between efforts to accomplish the task also load the tendon (e.g., calf raises or
prepare the individual and potentially minimize the impact leg extensions). In addition, isolated exercises early in reha-
that pain and fatigue have on the test. bilitation require less skill on the part of the individual and
make it easier for the clinician to apply the correct intensity.
More complex movement patterns can be incorporated into
3 Heavy Slow Resistance Considerations the program once there is a base tendon capacity established
that is sufficient to afford movement solutions that direct
3.1 Relative Submaximal Lifting Capacity sufficient load through that tendon.

Individual factors influence the ability to attain sufficient 3.2 Time Under Tension and Relative Submaximal
intensity in HSR training. The training background of the Lifting Capacity
person is critical to understanding their RSLC. For example,
total repetitions achieved on the leg press at 70% RM varied The second key variable that HSR addresses is the rate
widely based on training history: individuals who trained for of loading, which can be visualized as the slope of the
endurance completed 39.9 (± 17.6 reps) compared to those force–time curve during the time interval from onset of
who trained for strength (17.9 ± 2.8 reps) [10]. The ability movement to peak force. If loaded too rapidly, the tendon
to complete repetitions at a given %RM has been termed responds elastically with less strain and will adapt differ-
“relative submaximal lifting capacity” (RSLC). This RSLC ently than when loaded at a slower rate [7]. In HSR a slow
is influenced by a variety of other factors as well, such as lifting tempo is used as a surrogate for controlling this rate
the training status of the individual with trained individuals of force development. Repetition speed has a significant
Putting “Heavy” into Heavy Slow Resistance

impact on RSLC and is not controlled for in most of the lifting velocities with the impact they have on intensity. This
available RSLC research. To control this parameter when is especially important for the clinician using a repetition-
examining the 1RM prediction tests, Reynolds et al. used a based goal of more than six repetitions while also using the
metronome with a 1-s eccentric and 1-s concentric tempo, commonly prescribed 6 s/rep tempo. Abandonment of these
i.e., 30 repetitions per minute (r/m), to pace their exercise slower tempos is not the only way to maintain high intensity
[13]. This tempo is much quicker than most HSR studies, as this issue can be easily addressed in a few ways. If the
which take 6 s per repetition (10 r/m) or 8 s per repetition slower repetition velocity is deemed important, it can be
(7.5 r/m) [1–5]. maintained while lowering the repetition goals and therefore
The total time under tension (TUT) is defined as the time increasing the intensity that can be utilized. There are estab-
spent with the muscles under load and is determined by total lished training approaches that balance these constraints,
repetitions and the speed of each repetition. However, TUT may such as cluster training [16]. This approach keeps intensity
be more of an artifact of the rate of movement used during a high by programming in short intra-set rest periods, which
set than an important contributor to training effects. Instead, allows incomplete recovery between small “micro sets” to
the duration of each repetition will affect the training inten- allow more volume at a higher load. These “micro sets” are
sity used if volume is held constant (i.e., lifting a maximum performed with a load of sufficient intensity and at volumes
weight for the same number of repetitions but at different rep- that allow their execution at the prescribed rates (e.g., 85%
etition durations). In addition, decreasing the speed of repeti- RM lifted for 3 × 3 reps with 15 s rest between each set of
tion (e.g., 4, 8, or 10 s) will significantly impact the number of three) This allows for the accumulation of volume without
repetitions that can be performed at the same load [14]. Wilk sacrificing intensity by using strategic rest periods. This
et al. found that exercise volume was lowest for sets using the solution addresses the issues discussed in this paper without
slower repetition tempo, showing that even a small change in compromising any of the aspects currently deemed impor-
repetition tempo can significantly reduce the training volume. tant for the exercise-based management of tendinopathy.
This was examined in the bench press at five different loads It is important to ensure that the goal of rehabilitation
(40–80% 1RM) at tempos of approximately 2.8/1.4/1.0 s for drives the process of rehabilitation. If the goal is adapta-
the eccentric and concentric portion of the lift (5.6/2.8/1.9-s tion due to heavier loads, then these considerations will
lifts) [15]. It was shown that slower repetition speeds drasti- be important for clinicians and researchers. While moving
cally impact the RSLC with the weight lifted dropping below forward with the management of tendinopathy, it may be
70% RM at the sixth repetition for the slow group while the necessary to ensure that the “heavy” is put into the heavy
tempo was no longer maintained by the fourth repetition [15]. slow resistance approaches.
These data show that slower tempos at equivalent repetition
zones reduce the intensity of the load that can be lifted. This Declarations 
reduction in RSLC appears to dip below the necessary 70% RM
intensity threshold at around six repetitions when using a 6 s/ Funding  No sources of funding were used to assist in the preparation
of this article.
repetition (s/rep) tempo. Since HSR protocols frequently use
a 15/12/10/8 repetition approach at 6 s/rep, all of these repeti-
Conflict of interest  Scot Morrison and Jill Cook declare that they have
tion ranges exceed the probable maximum number that can be no conflicts of interest relevant to the content of this article.
performed at the desired intensity. This strongly suggests that
the intensity being used is not reaching the levels likely to elicit Availability of data and material N/A.
adaptations. Despite this, some good results have been seen
Code availability N/A.
with the HSR approach. This suggests that these outcomes are
likely based on something besides adaptations to high load. It Authors’ contributions  Substantial contributions to conception and
is interesting that Riel et al. were unable to replicate previous design: SM. Drafting the article or revising it critically for important
results for relief of plantar heel pain [5]. However, based on the intellectual content: SM, JC. Final approval of the version to be pub-
lished: SM, JC.
very slow tempo (8 s/rep) used in their study, their discussion
about under-dosage would make sense considering the impact
tempo has on relative intensity at a set repetition range. Open Access  This article is licensed under a Creative Commons Attri-
bution 4.0 International License, which permits use, sharing, adapta-
tion, distribution and reproduction in any medium or format, as long
as you give appropriate credit to the original author(s) and the source,
4 Discussion and Conclusion provide a link to the Creative Commons licence, and indicate if changes
were made. The images or other third party material in this article are
included in the article's Creative Commons licence, unless indicated
In conclusion, while slow tempo can be a practical cue to otherwise in a credit line to the material. If material is not included in
assist with coaching lower rates of lifting, these are not the article's Creative Commons licence and your intended use is not
equivalent concepts and it may be important to balance slow permitted by statutory regulation or exceeds the permitted use, you will
 S. Morrison, J. Cook

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copy of this licence, visit http://​creat​iveco​mmons.​org/​licen​ses/​by/4.​0/. ing and long-term adaptations: effects of muscle length, inten-
sity, and intent: a systematic review. Scand J Med Sci Sports.
2019;29:484–503.
9. Quinlan JI, Franchi MV, Gharahdaghi N, et  al. Muscle and
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