In an earlier article I discussed the differences between the two “pure” isometric muscle actions, the holding isometric muscle action (HIMA) and the pushing isometric muscle action (PIMA). I also touched on the Eccentric Quasi-Isometrics, explaining that these were out of the scope of the article and instead referred the reader to a fantastic review by Oranchuk and colleagues [1].
In this article I’ll be taking more of a look at these Quasi-Isometrics. I like the definition of “quasi” from the Cambridge dictionary; when used as a prefix the term quasi means “to a degree, but not completely”. Quasi-isometric could then simply mean – a muscular action in which tension is developed, “where to a degree, but not completely”, there is neither shortening nor lengthening of the muscle. In Quasi-isometrics the intent is to be isometric, and it looks isometric to the eye, but in reality, it is not truly isometric. As we know from my earlier article, “pure” isometrics are also not truly isometric as there are constant oscillations of shortening and lengthening of the muscle [2] and with tendon creep there is also progressive shortening of the muscle [3]. Despite this, to the eye, both HIMA and PIMA look and feel like static muscle actions.
In coaching terms Quasi-isometrics can simply be defined as dynamic isometric muscle actions, where rapid isometric stabilisation is attempted immediately after a dynamic movement. A good example of a Quasi-isometric is an altitude landing, where you drop from a box and land in a predetermined static position, attempting to minimise compression of the leg spring at ground contact. Quasi-Isometrics are part of a sub-group of isometric strength training (IST) methods, referred to as Pseudo-Isometrics.
PSEUDO-ISOMETRIC STRENGTH TRAINING METHODS
There are two sub-groups of IST, we have the Pure-Isometrics and we have the Pseudo-Isometrics. Within the Pseudo-Isometrics we have Quasi-Isometrics, Eccentric Quasi-isometrics, Oscillatory-Isometrics, and Isotonic-Isometrics to name a few distinct methods. Many of these methods have not been thoroughly researched and instead appear mostly in coaching manuals, textbooks, and online resources. However, disregarding these methods of training because they aren’t peer reviewed is extremely limiting in my opinion. Before going into some detail on Quasi-isometrics let’s look at some of these Pseudo-isometric methods.
Eccentric Quasi-Isometrics
What
A failed HIMA that becomes a maximally resisted eccentric muscle action is essentially an Eccentric Quasi-isometric. An example of an Eccentric Quasi-isometric would be a leg press held at 140 degrees knee extension with a maximal repetition duration load that induces HIMA failure within 30 seconds. When HIMA failure occurs, the muscles start to lengthen, and the exercise essentially becomes an eccentric exercise as the athlete attempts to control the lowering of the weight.
Why
Eccentric Quasi-isometrics is a method of resistance training that appears to be most beneficial for morphological adaptation at the muscle-tendon level as it lacks the neuromuscular specificity for high velocity movements.
How
Eccentric Quasi-isometrics are often placed in early preparation periods as an important time to maximise morphological and architectural adaptations and due to the high levels of fatigue they often induce. In either a team or individual sport setting Eccentric Quasi-isometrics of the lower body might be best placed in the off-season or in early pre-season where running and higher intensity training demands are lower and the need for transfer to higher velocity movements may be less time critical. Eccentric Quasi-isometrics may be used deeper into the pre-season but consideration around the content of training over the following 48-72 hours needs to be considered given the level of fatigue and muscle soreness that can be experienced after this form of training.
In a recent presentation with Victoria University Dr Andre Nelson and Dr Dustin Oranchuk recommended training loads of between 40-80% of concentric 1RM and total work time per repetition of between 40-60 seconds for Eccentric Quasi-isometrics. Within this total work time, a 30-40 second HIMA to failure and a 10-30 second controlled eccentric muscle action through to end range is performed. Normally just 1-2 sets of Eccentric Quasi-isometrics are performed per exercise. As an aside, in my experience, for HIMA failure to occur around the 30-40 second mark a load of between ~80-90% of an equivalent maximal PIMA should be used.
Oscillatory-Isometrics
What
Oscillatory-Isometrics have become popular in modern coaching circles, with a variety oscillatory type work implemented by leading practitioners over recent years. Oscillatory-Isometrics are performed in “semi-static” positions with pulsating movements over small joint ranges.
Why
During this pulsating movement there is constant and rapid contraction and relaxation of a targeted muscle or muscle groups. Proponents of Oscillatory-Isometrics suggest that reciprocal inhibition is brought about by these oscillations of rapid contracting and relaxing muscles. If this does occur, then an increased level of neuromuscular activation leading to increased rate of force development may be the result. Not only might Oscillatory-Isometrics increase rate of force development, but they may also influence the rapid relaxation of muscles which might also be an important factor in dynamic athletic performance.
How
Using the same leg press example, an Oscillatory Isometric commences holding the sled at 140-degree knee bend before rapidly pushing the sled to a 150-degree knee bend and rapidly relaxing, returning the sled back to the 140-degree position. This is then repeated consecutively and rapidly for a set number of “pulses” or a set time. The number of pulses prescribed seem to fluctuate from as little as 3 pulses up to as many as 20+ pulses, while the time periods are anywhere from 1-10 seconds long. Many coaches mix either a single or several full isotonic repetitions between series of pulses. In using a mixed method approach (incorporating isotonic lifting along with isometrics) some of the benefits of pure IST, like lower mechanical damage, lower fatigue, and the ability to perform a higher frequency of training are negated.
Loads used during Oscillatory Isometrics are submaximal and so stress to cause neuromuscular adaptation is low. Any neuromuscular adaptation is likely to be primarily driven be the rate of muscular contraction. With the use of lower loads Oscillatory Isometrics have been used as part of a successful peaking strategy. Anecdotally this Pseudo-isometric method may improve motor control strategies during peaking phases by assisting in overriding the inhibition of antagonist muscles. Due to the lower loads and minimal fatigue experienced in Oscillatory-isometrics multiple sets can be performed multiple times through the training week.
Isotonic-Isometrics
What
Isotonic-isometrics where popularised by Bob Hoffman of York barbell in the 1960s. They are essentially a partial concentric lift from a deeper position until the lift is blocked with some form of stoppers before a maximal PIMA is immediately performed.
Why
Isotonic-isometrics are a hybrid lift where a “best of both worlds” might be the training objective. An athlete can still achieve adaptation and potential transfer brought about by isotonic/concentric work while achieving some of the established benefits of IST within the same repetition.
How
Again, using our leg press example the athlete would lift the sled from a 90-degree knee position and then hit stoppers at a 140-degree knee bend where they would then perform a PIMA. The loads used in Isotonic-isometrics are high and they appear to bring about consistently higher force outputs in the PIMA. What’s really interesting with this Pseudo-isometric method is that there is a dual isometric muscle action where both types of Pure-Isometrics are performed at the same time. After the concentric lift the maximal PIMA is performed in driving the load into stoppers while simultaneously a HIMA is also performed with the weight clearly a moveable quantity that can drop should the requisite force to hold it against the stoppers be insufficient.
High stress is applied during Isotonic-isometrics. This will most certainly drive neuromuscular adaptations when incorporated into a well-balanced program. Again, some of the benefits of pure IST are negated using this “mixed method” approach, where isotonic lifting is incorporating with isometric lifting. Within training plans Isotonic-isometrics are best placed at time points in the preparation phase where isotonic lifting load can be modified to cater for training and competition demands. For example, in a block of training where additional fatigue can be tolerated, then the loads used in Isotonic-isometrics can be as high as 80-90% concentric 1RM, but when looking to reduce fatigue a load of 60-70% concentric 1RM might be preferred. In the latter option the main stimulus is clearly provided by the joint PIMA/HIMA rather than the isotonic lift.
Normally just the one working set of 1 repetition of 8-12 seconds is performed in a maximal Isotonic-isometric exercise. This is due to repetition duration reserve (RDR) becoming completely “maxed out” within this time frame. RDR is the amount of time the isometric action is performed for, as a percent of the maximal duration the isometric muscle action could be performed for, before failure or a reduction in force output is experienced. A maximal effort PIMA can only be sustained for approximately 10 seconds before there is a 5% drop in force output. Although I don’t advise regularly utilising 100% of RDR with high performing athletes, this is an important part of this Pseudo-isometric method that is touted to have made it such a potent training method. A more conservative approach that will allow 1-2 more quality sets, and double the total volume of work, would be to perform 4-6 second repetitions, which would correspond to an RDR of 40-60% and induce far less fatigue.
THE QUASI-ISOMETRICS
Again, with Quasi-isometric exercises there is an attempt to be isometric while an external force acts against the system and likely forces the muscles to lengthen momentarily. If the load is light or manageable then the muscles can brace isometrically but if the load is too great the muscles will perform eccentrically to decelerate the load. The “load” can come from body mass in landing or striking the ground like for example an altitude landing, or it might be from catching a barbell in a braced position after a barbell throw. Using the leg press example again, the leg press sled might be thrown and then caught in a predetermined braced isometric position.
Pre-tension and loading rates
A key differentiator between Quasi-Isometrics and the other Pseudo-Isometrics, is the requirement to create an appropriate level of pre-tension, also known as pre-load and pre-activation, before the acceptance of load. Pre-tension is a preparatory neuromuscular strategy used to optimize joint stiffness and stability prior to the acceptance of load. Pre-tension is considered a critical biomechanical factor for both athletic performance and injury resilience [5]. It is the ability of the neuromuscular system to anticipate the magnitude of load and respond with the appropriate level of muscle activity to either resist or attenuate impact force [6]. Pre-tension can certainly be considered as a skill, and when coupled with the underpinning isometric strength capabilities, appropriate pre-tension can be achieved by accurately anticipating impact force and effectively activating muscles to be able to rapidly produce force to resist joint deformation.
Due to the rapid receiving of load, loading rates are the highest of all the IST variants. Quasi-isometrics are really a dynamic exercise with very brief periods of static muscle action. With Quasi-isometrics being a dynamic exercise with high loading rates the external load used in is light in comparison to HIMA and PIMA exercises (for example 20-65% of the equivalent maximal PIMA load). These rapid loading rates and high impacts forces provide a substantial stimulus to the neuromuscular system. As far as lower body exercise is concerned, it is important to consider this Pseudo-isometric method similar to high intensity plyometric exercise when it comes to the placement of the training stimuli and the overall quantity of training.
Run Specific Quasi-isometrics
Knee Iso-Switch Impact Forces
Similar to plyometric exercise the Run Specific Quasi-isometric exercises can experience considerably high impact forces, especially when attempting to resist rather than attenuate impact force. For example, impact forces in high intensity bilateral plyometric exercises can range from 3.5 x body weight in a 46 cm drop jump to 5.4 x body weight in a 90 cm depth drop (or altitude landing) [7,8,9,10]. These forces are similar to the impact forces experienced in maximal velocity running, however, in these plyometric exercises the impact forces are shared between both legs [11].
In a Run Specific Quasi-isometric exercise like the Knee Iso-Switch, the stance leg is in a mid-stance running position when the recovery leg switches aggressively with the stance leg, coming from a thigh parallel to floor position to striking the floor with the mid-foot. Impact forces on the one leg can range from 3.6 x BW up to 6 x body weight (with equivalent maximal PIMA loads of 25% and 65% respectively). The Knee Iso-Switch exercise is generally executed with a brief bilateral load share which has the effect of slightly offsetting the load experienced on the striking leg.
The Advanced Knee Iso-Switch is a higher intensity variant that essentially eradicates the brief bilateral load share. It is executed with the thighs switching in front of the body while the body is in true flight. Impact force in the Advanced Knee Iso-Switch, as measured on the VALD Performance Force Decks force plates, have registered upwards of 7 x body weight using moderate loading schemes. It is recommended that when performing the Advanced Iso-Switch only the lighter loads are to be used (25-40% for example).
Again, it’s important to be aware of the high impact force that can be experienced with some Quasi-isometric exercises. The placement and quantity of these exercises needs to be considered around other high impact loading elements of the sport and S&C programme. For example, high-speed running loads and plyometric loads need to be considered along with Knee Iso-Switch loading. (insert Figure 1. Somewhere here)
Quasi-isometrics normally feature later in preparation phases once tissue properties and neuromuscular qualities are well developed. The development stage of the athlete and the training leading up to the implementation of high intensity Quasi-isometrics is crucial not only from a safety perspective but also from a performance perspective. As discussed earlier Quasi-isometrics require effective pre-tension and although effective anticipation accounts substantially, the capacity to tolerate the impact load needs to be developed in order to perform the Knee Iso-Switch effectively and avoid joints flexing and muscles lengthening beyond the predetermine position. As in the mid-stance phase of maximal velocity running the predetermined position for the Knee Iso-Switch is with knee flexed to 140-145 degrees (knee fully extended being 180 degrees) and hip flexed to 160-165 degrees (hip fully extended being 180 degrees) [11]. Capacity to tolerate the high impact forces can be specifically developed through the long-term use of both maximal and ballistic PIMA and HIMA exercises at the joint angles and muscle specific length used in the Knee Iso-Switch landing position. The ballistic HIMA, referred to as the Ballistic Knee Iso-Hold is a perfect segway to the Run Specific Quasi-isometrics.
Unlike the prescription for HIMA and PIMA exercises, repetition durations/pushing and holding times are less important for Quasi-Isometrics. Again, the main objective in an exercise like the Knee Iso-Switch is to achieve high levels of pre-tension to be able to rapidly generate high rates of force immediately upon ground contact. Therefore, just 1 to 2 seconds of holding in order to reset effectively are generally all that’s required. Due to the high intensity nature of the Knee Iso-Switch exercise, prescription normally ranges from as little as 4 to 18 repetitions in total. However, this can vary up to higher volumes of work of 50 repetitions with reductions in load and intent of the exercise or when other elements of the program have been well considered.
Knee Iso-Catch Impact Forces
The Knee Iso-Catch is another Run Specific Quasi-isometric exercise. There is a similar theme and rationale to the Knee Iso-Switch, in that the greatest challenge is to create the appropriate level of pre-tension to effectively hold joint positions at ground contact. The major difference, and the key factor that makes this exercise a higher intensity option, is that with the use of a jump the centre of mass is now propelled vertically and gravity accelerates the system (athlete and additional load) down to the ground with the athlete required to land at the established mid-stance joint angles and corresponding muscle lengths.
Much like a depth drop or altitude landing, but with additional load to compensate for the lower dropping heights. This is an important factor and a reason why the Knee Iso-Catch may be more effective than an altitude landing. As drop height increases in an altitude landing the vision and knowledge of drop height effect landing stiffness with more compliant strategies used to dissipate landing forces [12]. This effect is amplified when the athlete must land with one leg with heightened anticipation of total landing forces to be absorbed in unilateral stance. In a Knee Iso-Catch the application of load adequately makes up for a much lower drop height and avoids the negative anticipatory and regulatory responses associated with landings from height. The increase in leg stiffness during a Knee Iso-Catch further increases the impact forces experienced and collectively, height, load, stance, and level of stiffness, provide for a very intense loading stimulus.
As found on the VALD Performance Force Decks force plate system, a Knee Iso-Catch with the lightest recommended load of 20% of an equivalent maximal PIMA, can incur impact forces of over 3.2 x body weight with just a 10 cm displacement. Performing a Knee Iso-Catch with 25cm of displacement can lead to impact forces over 4.6 x body weight and when using 35% loads impact force can reach well above 6 x body weight. Again, due to the high intensity nature of this exercise loading is lighter than in the Knee Iso-Switch and a maximal total volume of approximately 15 contacts is recommended.
In summary:
- There are two subgroups of IST exercises: the Pure Isometrics and the Pseudo-Isometrics.
- There are a range of Pseudo-Isometric strength training exercises that seem to have a substantial adaptive response, yet there is a paucity of research in the area.
- A unique stream of Pseudo-Isometrics is the Quasi-Isometrics which are characterised by the requirement for pre-tension before the acceptance of load in predetermined joint positions.
- Quasi-Isometrics can be performed in running specific positions using the Knee Iso-Switch and the Knee Iso-Catch.
- Impact loads experienced in the Run Specific Quasi-Isometrics can be greater than those experienced in plyometric activities and maximal velocity sprinting.
A final note:
Extreme care is to be taken with both Run Specific Quasi-Isometric exercises; the Knee Iso-Switch and the Knee Iso-Catch. Again, these are both very high intensity exercises that elicit extreme impact forces. Many months of training, let alone years of gradual progressions are necessary to safely execute and get the most out of both of these Run Specific Quasi-Isometric knee exercises. In fact, the majority of athletes will achieve long and sustained benefits using the Run Specific PIMA and HIMA. The Run Specific Quasi-Isometrics should be reserved for those few athletes who have “earned the right” or specifically for athletes returning to running performance post lower limb injury.
Reference List
- Oranchuk, D., Storey, A., Nelson, A. and Cronin, J. Scientific basis for eccentric quasi-isometric resistance training: a narrative review. J Strength Cond Res. 2019; 33 (10): 2846-2859.
- Schaefer, L., Hoff, M. and Bittmann, F. Measuring the adaptive force. Eur J Transl Myol. 2015; 27 (3): 152-159.
- Mademli, L. and Arampatiz, A. Behaviour of the human gastrocnemius muscle architecture during submaximal isometric fatigue. Eur J Appl Physiol. 2005; 94: 611-617.
- Donoghue, O.A., Shimojo, H., & Takagi, H. Impact Forces of Plyometric Exercises Performed on Land and in Water. Sports Health. 2011; 3: 303 – 309.
- Tam, N., Santos-Concejero, J., Coetzee, D., Noakes, T., Tucker, R. Muscle co-activation and its influence on running performance and risk of injury in elite Kenyan runners. Journal of Sports Science. 2017: 35 (2): 175-181.
- Tam, N., Tucker, R., Santos-Concejero, J., Prins, D. and Laberts, R. Running economy: neuromuscular and joint-stiffness contributions in trained runners. International Journal of Sports Physiology and Performance. 2019: 14: 16-22.
- Jensen, R. and Ebben, W. Quantifying plyometric intensity via right of force development, knee joint, and ground reaction forces. Journal of Strength and Conditioning Research. 2007; 21 (3): 763-767.
- Jensen, R. Kinetic responses during landings of plyometric exercises. Motor Performance and Control. 2008; 393-396.
- Wallace, B.,White, J., Kernozek, T. and Kline, D. Quantification of vertical ground reaction forces of popular bilateral plyometric exercises. Journal of Strength and Conditioning Research. 2010; 24 (1): 207-212.
- Jensen, R. Ground reaction forces of variations of plyometric exercises on hard surfaces, padded surfaces and water. In proceedings of the XXVIII conference of the International Society of Biomechanics in sports. 2010; 533-536.
- Sides, D. Kinematics and kinetics of maximal velocity sprinting and specificity of training in elite athletes. PhD Thesis. 2015; pg 146.
- Santello, M., McDonagh, M., Challis, J. Visual and non-visual control of landing movements in humans. Journal of Physiology. 2001; 537 (1): 313-327.
