The Science of Core Training: Training Methods & Application (Part 2 of Core Training Series)
Part 2 of this core stiffness article series will cover the core training principles and methods that drive short and long-term improvements in performance.
Read Part 1 Here
In part 1, I went over what the core is and the function of core stiffness in relation to sporting performance and optimal force and power output. To recap: core stiffness may refer to the core's ability to maintain stability in response to the influence of external forces, which may vary in magnitude, direction and speed.
Highly recommend reading part 1 before continuing on with this article.
In part 1, I mentioned that improving performance via increased core stiffness will depend on multiple variables:
The nature of the sport and the energy systems involved (How long is the core braced for? Does the athlete need more strength? Or more endurance?)
The particular movement you're trying to improve by increasing core stiffness
The properties of the movement itself and the speed of core stiffening
The magnitude of core stiffening (stiffer doesn't always mean better, remember: fast and powerful athletes also need to learn how to relax at the right times - like the example of the punches and kicks we used earlier).
First off, I'd like to break this article up into 2 categories, short-term improvements in core stiffness and long-term improvements in core stiffness.
SHORT-TERM IMPROVEMENTS
Short-term improvements or increases in core stiffness, are characterized by improvements seen within the same training session. Known and performed as "core activation" drills among personal training circles, some claim that performing core exercises prior to the main exercises of a workout "wakes up" the core and improves performance on the subsequent exercises. While terms like "wake up" are very arbitrary, it helps to look a potential mechanism by which core activation drills help with short term performance.
Post Activation Potential
Benjamin Lee and Stuart McGill carried out a study in 2017 to measure the effects of short-term isometric training on core torso stiffness and found beneficial results. For the core isometric training protocol, participants performed the plank, side plank and bird dog exercises for 5 sets of 10 seconds - with coaching cues being offered and standardized to all participants. Using both passive and active torso bending trials, the results showed that most participants had reductions in torso deflection and increased core stiffness (more details here).
While this study showed that short-term core stiffness can be increased via isometric core exercises, it doesn't tell us how that core stiffness will transfer to performance in other exercises, or how long this effect lasts. In their discussion, the authors pointed to the fact that the isometric exercises done could have elicited a post activation potential (PAP).
PAP is a physiological/neurological phenomenon where strength and rate of force development (power) is increased due to previous near-maximal muscle contractions. The most common protocols may include heavy back squats to elicit a PAP effect before sprinting and jumping, or heavy presses before performing ballistic medicine ball pushes/throws. Utilizing the PAP effect is also known as complex training. Here are some examples of exercise pairings, from the NSCA.
Taken from https://www.nsca.com/Education/Articles/Hot-Topic-Post-Activation-Potentiation-%28PAP%29/
For a concise explanation of the potential mechanisms behind PAP and how it works, visit Science For Sport.
Back to the study. While the authors pointed out the PAP mechanism, they acknowledged that their core training protocol, despite improving core stiffness, did not meet the requirements of a "potentiating exercise". In a standard PAP protocol, the potentiating exercise has to be close to max effort, with the recovery time reflecting the nature of exercise. Lee & McGill's (2017) study's core training protocol included 5 sets of non-fatiguing core exercises (only 10 seconds long - bodyweight, no added resistance), so I'd be interested to see if there could be a larger PAP effect if some core exercises are taken to near max effort. Here are some ideas:
Complex Training For Core & Power Exercises
Weighted Planks into Medicine Ball Slams (2-3 minute recovery)
(3-6 complex sets of <30sec weighted planks into 4-8 max effort slams)
Planks are one of the most frequently prescribed core exercises in the fitness and strength training. An easy way to increase the difficulty of the plank is to add extra resistance - perform them weighted. In this complex set, the weighted planks act as the potentiating exercise, increasing the the power output of the slams. While the effort should still be high during the planks, the physiological stress is relatively low compared to for example, a set of heavy front squats; meaning the recovery time should be lower than most heavy compound movements. A recovery time of 2 minutes should be adequate before performing the medicine ball slams.
Squatted Pallof Press Into Rotational Medicine Ball Slams/Throws (1-2 minute recovery)
(3-6 complex sets of 6-8 presses into 4-8 max effort slams/throws)
In this example, I use an anti-rotation exercise to potentiate a ballistic exercise for better power transfer. I also added a small rotation component to what would normally be an anti-rotation exercise (the pallof press) to mimic some of the movements seen in the medicine ball rotation throw. Keep in mind, I still maintain tension on my obliques working and the shoulder girdle stable during the press out and rotation. Recovery time can be anywhere from 1 to 2 minutes.
Other Potential Ideas
Core Stiffness For Powerlifting
Aside from using higher effort complex sets, I have found situations where non-fatiguing core exercises can help improve the quality of a training session. For the last couple of months, I've been using bodyweight planks and shorter weighted plank sets with my powerlifters prior to the main compound lifts . Planks are a good way to emphasize whole body tension (a skill that is required for powerlifting success), to improve the lifters' perception on how active their core for the rest of the training session, and to remind them about the importance of a rigid torso during the powerlifts. Most, if not all of my powerlifters, have found this pre-lifting core work beneficial.
With this protocol, perform several sets of planks at a low RPE (non-fatiguing) to avoid overly fatiguing the core musculature before the compound lifts. More advanced trainees can experiment with planks at higher intensities to elicit a greater PAP response. Slowly increase the intensity of these planks over time to find the sweet spot (balance of volume and intensity).
Core Stiffness For Weightlifting
Another idea I've implemented in the past is the use of higher velocity core stiffening drills to help facilitate weightlifting technique improvements. The catch position of snatches and cleans require a lifter to quickly decelerate the weight by using the prime movers and stiffening the core upon bar contact. I've found depth drop landings or plyometric regression exercises to help with this. Here's a quick example with one of my Strongman/Powerlifting athletes, who was brand new to the Olympic lifts at the time. Used in conjunction with other coaching techniques, he made some good improvements just over the span of 3 months.
Intra-abdominal Pressure (IAP)
If you've spent anytime studying strength training or have spent time in the weight room, you probably heard of the concept of intra-abdominal pressure (IAP). Also referred to as "bracing", intra-abdominal pressure is a technique by which a trainee creates 360 degree pressure in the abdominal cavity through controlled inhalation. The created pressure helps stabilize the lumbar spine, reduce the risk of back injuries as well as improve force output. The concepts of core stiffening and creating intra-abdominal pressure are complimentary and much like the core stiffening concepts discussed previously, IAP is not an all or nothing phenomenon.
IAP happens on a continuum, and can vary in intensity and duration depending on the movement requirements of the task. Coaches around the world all stress the idea of creating IAP during strength training, however, not many of them can explain it as well as Chris Duffin (Kabuki Strength) and Stuart McGill. Kabuki Strength describes IAP as a continuum of respiration (breathing) and stabilization (max effort IAP), best represented by a dial.
To give an example, the lumbar stability needs during a 1RM compound lift is different than a sub-maximal activity like running. Running requires just enough IAP to stabilize the torso, while still allowing for optimal breathing. Turn the knob accordingly.
““Improving your ability to select and coordinate the correct dial setting is the key for fluid movement and higher performance in any activity””
long-term improvements
Long-term improvements in core stiffness are characterized by improvements seen over weeks and months of core training. This section will cover the different categories of core training, as well as general training principles that drive long term improvements.
Core Training Categorization
To start, it's best to differentiate between core exercises in order to better analyze their cost-to-benefit ratio. All exercises fall on a general to specific continuum, with the reference points being the movement you want to improve, or the sport/position you're playing - core exercises are no different. Dedicated core exercises can be broken down into several categories:
1. Isometric Core Exercises
Isometric exercises are exercises where force is produced without a change in muscle length. Exercises like planks and hanging L-Sit where you're maintaining your body position are examples of isometric core exercises.
2. Anti-Rotational Core Exercises
Anti-Rotational exercises also fall the "isometric" category. These exercises challenge your ability to stabilize your body to prevent from rotating to any one side, maintaining your body position against an external force or in an imbalanced position. Common exercises include the pallof press, shoulder taps in push up position and many exercises in the half kneeling position. Other great examples not many people know about could be suitcase deadlifts, and uneven farmers walks (videos below).
3. Isotonic Core Exercises (Sagital Plane/Transvere Plane)
Isotonic exercises are exercises that consist of an eccentric and concentric portion - exercises that are not isometric (holds). They can be further broken down into sagital/transverse plane exercises. Sagital plane exercises include standing cable crunches, sit ups and hanging leg raises, while transverse plane exercises involves any exercise that involve torso rotation like cable wood-choppers and medicine ball russian twists.
4. Ballistic and Plyometric Core Exercises
Ballistic exercises are concentric-dominant power movements with little to no eccentric muscle action, such as jump squats and explosive push ups. In the realm of core exercises, medicine ball slams, rotational throws can be considered ballistic, but keep in mind the prime movers such as the shoulders and glutes also contribute to the force output.
Plyometric exercises are exercises with a short eccentric-concentric turnover, using the elastic properties of our muscles to improve speed and repeated power output. Many movements like running, repeated jumps/hops and combination striking (in martial arts) are considered plyometric. There are also plyometric exercises designed just to target the core musculature - many of these being rotational. I've posted a few examples below:
Taken from Nick Curson (Speed of Sport)
Taken from Elliot Hulse
Training principles and methods To Improve Performance
Conversations usually go south whenever the topic of "transfer to performance" is brought up; there are many complex variables to take into consideration and everyone seems to have their own definition of "functional" or what exercises will and will not help improve performance. I'll be giving some general tips and training principles of core training that can be applied to various different sports.
Post-activation-potentiation, non-fatiguing core primers and intra-abdominal pressure are all acute techniques that CAN lead to long-term improvements
The research is still not conclusive on whether these are significantly beneficial, but in theory: accumulating small short-term improvements should lead to long term improvements in performance. In other words, if these techniques are performed consistently throughout your training program, they may add up to a measurable increase in strength, power and endurance (whatever you're aiming for). I would also add that the use of PAP and core primers are optional, but in my opinion, IAP is not. I consider IAP a skill that must be learned and utilized consistently in order to effectively produce force, and stay safe doing so.
A combination of general and specific core exercises should be performed
Don't fall into the "functional" trap of prescribing overly-specific exercises. A general exercise that does not fully mimic the movement you're trying to improve can still be beneficial. For example, weighted planks are a great general core exercise to build core strength and endurance that will transfer over to various movements. Once a good base is built, you can start experimenting with more specific exercises. I've included some examples of specific exercises at the end of this article, mainly geared towards improving punch power, but can also be used as core training.
To learn more about the general-specific continuum and how to classify exercises for better training prescription, read my article I wrote on training variation here.
Principle of progressive overload
This is the premise behind improving any type of performance measure. Progressive overloading your core exercises either through a change in position, adding extra resistance, increasing the volume via sets, reps or time. In order to improve, you must progressively add stress to your physiological system, recover from it, and come back stronger.
Improving Core Strength (Slow-Isometric Stiffness)
Core strength, or slower-isometric type core stiffness, is primarily built using isometric and anti-rotation based exercises. Almost every core exercise listed above can be used to improve core strength, but what differentiates training core strength from core endurance is the intensity at which these exercises are performed. Reps should be done in the lower rep range (~<6 reps per set) or 80-95% of 1RM if a 1RM is applicable. Accordingly, intensity/weight progression is what you should be focused on. For example, progressively working towards heavier weighted planks (increasing intensity) instead of increasing the time of which you hold body-weight planks. Improving core strength will benefit every athlete, but strength and power athletes will see the best results.
Improving Core Ballistic/Plyometric/Power Ability (Fast-Recruiment Stiffness)
Core plyometric ability, or what I like to describe as a faster-recruitment type core stiffness, is built through plyometric core exercises and have a higher skill/timing component to it. This is the type of core stiffness I discussed in part 1, that is required for high-impact athletes who perform punching, kicking and striking movements. The ability to contract-relax-contract and produce a fast eccentric-concentric turnover is what defines an athlete with good core power and plyometric ability - both deceleration and acceleration are taken into account.
I gave examples of relatively advanced plyometric core training above (see Nick Curson and Elliot Hulse's videos). A more beginner friendly way to perform these exercises would be to reduce the range of motion on the exercises and reduce the power output until you improve your timing. A drill I found useful are short plyometric medicine ball rotation slams - timing and rhythm are paramount here so develop them before moving onto higher-intensity, higher-effort plyometrics.
Improving Core Endurance
When people think of the word "endurance" they immediately associate that with a low-intensity, long duration training protocol. Don't make the same mistake. Endurance can refer to the ability to maintain a certain power output for an extended period of time OR be able to repeatedly perform high-intensity bouts with little to no drop off in power output from start to finish. I recommend using work-to-rest ratios with your core exercises based on the energy system you want to develop.
Do you want to be able to repeat maximal high-intensity efforts? Use work rest ratios anywhere from 1:20 to 1:30+. For example, 6 seconds of maximum effort tornado ball slams with 2 minutes of complete rest in between sets, for several sets (1:20 work-rest ratio).
Looking to improve anaerobic capacity? Use work-rest ratios around 1:1. For example, 60 seconds of moderately heavy farmers walks with 60 seconds of active rest in between sets (1:1 work-rest ratio).
Looking for longer duration core endurance? Perform lower intensity core exercises for a total of 3 minutes+ at a time with a work-rest ratio of ~2:1. For example, hold a bodyweight plank for sets of 3 minutes with 1.5 minute rests in between. To add some variation to these longer sets, you can also perform 3-4 different core exercises as a circuit for 1 minute each. Over time, increase the duration of each set or the total number of sets (volume load progression at a set intensity).
Using work-to-rest ratios is another tool by which you can use to look at and utilize core training with. It can help you visualize which energy systems are at play, so you can make the adaptations you want to see. Endurance is specific.
Diminishing Returns
More core work means better performance right? Not so fast. Welcome to the principle of diminishing returns. The more you train core stiffness, the less benefits you reap in. I see core stiffness training a lot like maximal strength for sports. There comes a point where more core training does not equate to better performance on the field, court, platform or ring. Core stiffness, much like strength, serves as a foundation on which other important physical attributes are built on - rate of force development, agility, resilience to injury to name a few. Be careful not to allocate all of your time and energy into core stiffness training, while neglecting the development of other skills and attributes.
So how much is enough?
Unfortunately, I don't have a concrete answer for you. This really depends on what sport and movement patterns you're referring to. Core training should fill the gaps of your physical development, and be used in conjunction with sport-specific skill work and strength/power/plyometric training. Being able to competently perform all the movement patterns and core exercise categories listed above is a great start.
Biggest takeaway
If there's one thing you take away from this article, it's that core stiffness training is context-specific and should be thoughtfully prescribed and developed. Core training does not have to be boring, so don't be afraid to get creative. Below is some of my content I've put out on core training, core ballistic training and various medicine ball slam exercises. Thanks for reading!
ARTICLE: Great Core Exercises You're Not Doing
CORE TRAINING VIDEOS:
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The Science of Core Training: Core Stiffness & Performance Overview (Part 1 of Core Training Series)
This article will overview the concept of core stiffness and how it's applied to several sporting performances and movements. Core stiffness may refer to the core's ability to maintain stability in response to the influence of external forces, which may vary in magnitude, direction and speed.
Core training has been all the hype the last several years - from an aesthetic point of view (achieving 6 pack abs) to it's potential role in reducing lower back pain and related symptoms. This article won't be touching on any of those points. I'm speaking more from a performance-enhancement perspective, specifically, the role of core stiffness and it's relation to performance outcomes.
What is the "core"?
The musculature and structures between your shoulder girdle and your hip; the superficial and deep abdominal muscles.
What is the function of the "core" and what is "core stiffness"?
Ask a performance coach and they'll give you one answer. Ask a physical therapist and they might give you a different one. From a physical therapy or rehabilitation setting, core stiffness may refer to increased muscle tone that leads to lower back pain and movement restrictions. In the performance sports setting, core stiffness may refer to the core's ability to maintain stability in response to the influence of external forces, which may vary in magnitude, direction and speed. For the purpose of this write up, I'll be talking about the latter.
To my knowledge, the function of the core is to transmit force, prevent force/power leaks and maintain the position of certain joints and body segments. In the words of professional lower back and spine expert Stuart McGill, he describes the function of the core to "stiffen the torso to prevent motion, [and] enhance motion of the distal limb segments".
In the majority of sporting performances, the ability to accelerate distal limbs is the key to high power output: think about throwing a baseball, kicking a soccer ball, jumping, pushing, punching. Stiffening the torso to prevent excessive motion and enhances force production and power output because it acts as a medium for force transmission - ensuring all the force you generated is directed towards your intended direction. A floppy and weak midsection results in a weak kick, a weak throw, a weak jump and a weak landing.
an overview, with examples.
The idea of core stiffness allowing for better force production/transfer can be applied to many different scenarios. I'll give 3 examples from 3 different sporting types, a mixed sport (Mixed martial arts/combat sports), an endurance-dominant sport (Cycling) and a strength-dominant sport (Powerlifting).
In each example, the RED highlighted area represents the "core": the superficial abdominal muscles (rectus abdominis), the deeper muscles like the transverse abdominis as well as surround muscles like the obliques (for rotation), latissimus dorsi and rotator cuff muscles.
The GREEN highlighted areas represent the prime movers that are responsible for generating force through concentric muscle action, and/or the distal limb segments that are used to transmit force into the intended direction or to move a certain object.
Example #1 - The Punch and Kick in Martial Arts
The straight right/left punch is one of the most basic, yet intricate techniques in martial arts. Contrary to what many think, the prime movers of the straight punch are actually the back leg, the muscles surrounding the hip and the shoulder girdle, NOT the arms. Power is generated by pushing off the back foot, contracting the glute, and directing that force into the distal limb segment (which is the fist in this scenario).
In order to effectively transmit that power from foot to fist, the core must rigid. The obliques must create enough deceleration force to prevent your torso from over-rotating (shifting you off balance), and your shoulder girdle must be sturdy enough so loosen up on impact. Additional, these types of movements (punches, kicks, hitting/impact-movements) exhibit a "double peak" in regards to muscle activity (measured through Electromyography (EMG)). In other words, whenever performing a powerful movement, the muscles will go through 3 phases: contract/stiffen, relax, and contract/stiffen once again upon impact, showing a "double" peak in activation (will be pictured below).
Stuart McGill et al. performed a study in 2010 on elite mixed martial artists (Georges St. Pierre, David Loiseau to name a few) that introduced me to this concept so I'm sure he can explain it more clearly:
“Many of the
strikes intend to create fast motion and finish with a very large
striking force, demonstrating a ‘‘double peak’’ of muscle activity.
An initial peak was timed with the initiation of motion
presumably to enhance stiffness and stability through the body
before motion. This appeared to create an inertial mass in the
large ‘‘core’’ for limb muscles to ‘‘pry’’ against to initiate limb
motion. Then, some muscles underwent a relaxation phase as
speed of limb motion increased. A second peak was observed
upon contact with the opponent (heavy bag). It was postulated
that this would increase stiffness through the body linkage,
resulting in a higher effective mass behind the strike and likely
a higher strike force.”
To further illustrate the "double peak" in activation, and to tie it back to the discussion earlier about prime movers and the core, here's a figure taken from McGill et al's 2010 study (green and red highlights made by myself).
This figure illustrates the muscle activation of the left back muscles during a left leg kick to a heavy bag.
Taken from McGill et al. 2010
#1 in green represents the initial activation of the muscle (phase 1 - contraction), where the foot pushes off the floor and the hip flexors and obliques contract in order for the leg to be lifted into the air. The prime movers are the hip, quadriceps and left back.
#2 in red represents the relaxation phase (phase 2) where the leg is in mid air and force is being transmitted through the core, to hit the intended target (shin/foot hitting the heavy bag).
#3 in green represents the second activation of the muscle (phase 3 - contraction again), where the muscles stiffen up once again on impact.
An athlete with a weak core, or an inability to stiffen up the core will experience power leaks in #2, which subsequently results in a lower striking force upon impact in #3.
Optimal force and power production happens when an athlete has:
Good body positioning
The ability to show double activation during strikes/impact movements
The ability to efficiently cycle through contract-relax-contract muscle action if repeated punches/kicks/impacts are performed
Strong and resilient core musculature.
Example #2 - cycling
Operating at up to 300RPM (revolutions per minute) and putting out up to 2,200 watts, track cyclists are known for their lower limb strength and power, as well as their ability to maintain extremely high power outputs for extended periods of time.
Watch the video below, notice the rigid and stable core - supported by the shoulders and arms, and how that translates to incredibly fast distal limb segment movement (in this case, the feet).
Yes, the thigh musculature are still the primary movers, but the core/torso also contribute greatly, acting like a shock absorber to negate most of the horizontal and vertical bodyweight shifting that happens during high RPMs. A strong core ensures as much of the force generated by the prime movers can be directed towards spinning the pedal.
Picture taken from TeamNater (Youtube), editted by myself.
The principles of contract-relax-contract discussed above also apply to this example. The quadricep has to relax while the hamstring is active during the (pedal) upstroke, and vice versa during the downstroke. Pair it with the fact that this is all happening at 150, 200, 250+ RPM and you'll realize the amount of motor control needed to be an elite cyclist.
Example #3 - Powerlifting
Our last example is a strength sport - powerlifting. Powerlifting is a maximal strength sport, meaning the velocity of distal limbs and the velocity of the bar is relatively low compared to other sports such as Olympic Lifting or various throwing sports. As a result, core stiffness plays a slightly different role - a slower isometric role. Although there is no contract-relax-contract cycle in powerlifting, the core still acts as a stopper for potential force leakages. The main role of the having a rigid torso/core is to support the lumbar and thoracic spine under heavy load.
In a sport where limb length and leverages are highly influential on performance outcomes, a lifter must maintain the position of their lumbar and thoracic spine so that their chest does not collapse under the weight, and their lower back doesn't go into excessive flexion. Losing position means the lifter will not be able to lift the weight up, regardless of how strong their prime movers are.
Below is an example of one of the lifters on my Powerlifting team, Amos So, bracing for a squat at a local powerlifting meet.
Context Specific
Throughout the article, I've used terms like "stable", "rigid", "strong" and "resilient" to describe the properties of a well-functioning core. Different coaches and trainers will use different terms to describe the core, so terminology is sometimes confusing.
However, what matters is how you apply these principles to your own training, or the training of your clients and athletes. Improving performance measures via increased core stiffness will depend on several things:
The nature of the sport and the energy systems involved (How long is the core braced for? Does the athlete need more strength? Or more endurance?)
The particular movement you're trying to improve by increasing core stiffness
The properties of the movement itself and the speed of core stiffening
The magnitude of core stiffening (stiffer doesn't always mean better, remember: fast and powerful athletes also need to learn how to relax at the right times - like the example of the punches and kicks we used earlier).
Much like the development of max strength for athletic performance, there are also most likely diminishing returns, so don't fall into the trap of "more core training = higher performance".
In part 2 of this series, I'll be explaining the different methods to improve core stiffness in the short-term and in the long-term.
Read Part 2 Here.
Thanks for reading, feel free to share this article with your peers and fellow coaches. Also, please check out my social media links and reach out to me if you have any questions or suggestions.