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.
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Off-Season Program for Size and Athleticism
I wanted to create a program for myself that incorporated Olympic weightlifting exercises once or twice a week without sacrificing time on bodybuilding and powerlifting movements. What initially started as a simple training split, developed into a well-rounded program for general strength, hypertrophy and athleticism. This program is by no means beginner-friendly; it requires you to have at least some experience with compound exercises (bench press, squats, deadlift, dips, overhead press etc) and Olympic weightlifting movements (power snatches, power cleans). In this blog post, I will do an overview of the whole program and highlight the details and nuances of each training mesocycle.
Program Overview
Training-Split Layout
MONDAY (Full body): Olympic Lifts w/ Front squats, Abs
TUESDAY (Upper body): Chest, Back, Biceps
WEDNESDAY: ACTIVE REST
THURSDAY (Lower body): Lower body with quadricep/squat focus
FRIDAY (Upper body): Shoulders, Chest, triceps
SATURDAY (Lower body): Lower body with posterior chain focus, Back
SUNDAY: Rest
3 Mesocycles
Weeks 1-3 is considered a high-volume hypertrophy block
Week 4 is an active rest/deload
Weeks 5-9 is considered a strength block (with Week 9 being a back off on volume (not a full deload)
Weeks 10-12 is a power and conditioning block
Frequency
Unlike a typical bodybuilding bro-split, frequency is moderate - high to ensure muscle protein synthesis (MPS) is kept above baseline for each body part throughout the whole week
The moderate-high frequency done in this program is also good for motor learning/technique-acquisition and improvement, as well as neuromuscular efficiency (with the exception of the Olympic lifts, which I will address in the final section of this post)
Quadriceps, glutes and hamstrings are all being hit 2-3 times a week throughout the whole program
Chest and triceps are being hit at least twice a week
Back and pulling movements are being done at least twice a week
Shoulders (specifically the lateral head of the deltoid) are only being hit once a week, but it should be noted that the anterior (front) and posterior (back) delts are stimulated on other days via pulling and pushing exercises anwyays
Ab exercises are included in the program at least once a week
Placement of Rest Days
Rest days are placed strategically to mitigate muscle soreness (delayed onset muscle soreness - DOMs) and ensure adequate muscle recovery
Wednesday's rest day is to ensure the lifter is recovered before 3 back-to-back sessions (Thursday, Friday, Saturday).
Monday is definitely the most technique-intensive day out of the whole program, therefore adequate muscle recovery (reducing DOMs) must be made during Sunday's rest day in order to reduce injuries and increase skill acquisition.
Adequate rest in between 2 sessions that stimulate the same muscles (eg: Chest is being stimulated on Tuesday, then again on Friday. Wednesday and Thursday gives a chance for the chest to recover; right when MPS of the chest drops back to baseline on Thursday, Friday's session will increase it once again up until Sunday/Monday)
Lower volume works requires less time to recover from (Thursday's posterior chain work is pretty low volume, therefore the posterior chain can be worked again on Saturday without any decreases in performance)
Spacing muscle groups out evenly throughout the week is essentially taking advantage of the Stimulus-Recovery-Adaptation curves of each muscle (concept taken from NSCA, Dr. Yuri Verkhoshanksy and Dr. Mike Israetel).
Weeks 1-3
Training Variables (Volume, Intensity, Frequency)
Week 1 starts off easy; volume ramps up every week, adding a set to most exercises will keeping the weights the same
Volume peaks at Week 3 (Week 3 should be brutal, you should be sore)
Since Week 1 is fairly easy, Wednesday will be an active rest.
Weeks 2-3 will be much harder and more taxing, therefore Wednesday will be a full rest (no lifting/little to no physical activity, but do stretch and foam roll)
Exercise Selection
More unilateral work (1 legged RDLs, Bulg. Split Squats, 1 Arm Pulling etc) in order to eliminate muscle imbalances and improve balance/coordination
There is more isolation and arm exercises (Biceps, leg extensions, rear delts etc) compared to Weeks 5-9
Muscle snatches and muscle cleans are used for the first 3 weeks to build up the shoulder musculature and to practice technique (bar acceleration, triple extension) in preparation for power snatches and cleans.
Snatch grip deadlifts with slow eccentrics are used to practice lat activation and increase hamstring hypertrophy in preparation for the conventional deadlifts in Weeks 5-9 (strength phase)
Main Focus
Weeks 1-3 are important for dialing in technique and setting a good base for the strength and power phases of the 12-week program
The focus should be on work capacity, and volume. Do not worry TOO much on weight progression, stay within 8-8.5 RPE (What is RPE? This is covered in the FAQs at the end of this overview) for most compound movements. Feel free to go to failure and apply a supersets/dropsets to isolation/accessory exercises.
Again, Week 3 should be very high volume. It should feel brutal and you should feel beat up.
Weeks 5-9
Training Variables (Volume, Intensity, Frequency)
Overall all weekly volume is decreased in the strength phase because the intensity is increased
Squat frequency goes up from 2x/week to 3x/week (Monday - Front Squat, Thursday - Back Squat, Saturday - Pause Back Squat)
Deadlift frequency stays at 1x/week, but stiff legged deadlifts are introduced in Thursday workouts
Focus on weight progressions through the weeks (eg: Week 8's 4x5 should be heavier than Week 5's 5x5 sets)
Volume drops on Week 9 in preparation for the power and conditioning phase in Weeks 10-12
Frequency of Power cleans increases from 1x/week to 2x/week (more practice!)
Exercise Selection
The focus shifts from dumbbell work into barbell work so you can handle more weight (Dumbbell RDL's into Barbell Stiff Legged Deadlifts, Incline Dumbbell Bench Press turns into Incline Barbell Bench Press)
A switch from muscle snatch and cleans to power snatch and power cleans
If you cannot get a hold of a glute-ham raise machine, do weighted lower back extensions
Conventional deadlifts replace snatch grip deadlifts (again, so you can handle more weight)
For triceps on Fridays, I recommend any of the following compound movements: 1) Close-grip bench press 2) JM Press 3) Dips 4) Lying Tricep Extensions (Rippetoe variation)
Main Focus
The main focus for Weeks 5-9 is to move heavy weight while still maintaining proper form (however, one should always seek technique improvement)
Stay within 8-9 RPE for compound exercises in Weeks 5-8. Stay within 7-8 RPE for Week 9.
Weeks 10-12
Training Variables (Volume, Intensity, Frequency)
Volume is very low to keep fatigue low. Low fatigue is the best environment to express and practice athletic characteristics such as power, speed and strength
Intensity should be high, you should be moving very heavy weight (>85% of your 1 rep max) for a few reps and sets
Frequency of the main lifts do not change
Conditioning exercises can be done by feel, the sets and reps written down are very rough, do what feels good. Stop when you notice a large decrease in your speed and effort
Exercise Selection
This power and conditioning block focuses on a lot on heavy lifting, mixed with explosive power movements
Introduction of medicine ball exercises are good for working on rotational power (transverse plane of motion)
Box jumps can include any variation of your liking, normal box jumps, rotation box jumps, depth jumps etc.
Snatchs and/or cleans can be substituted by power snatches and power cleans if your snatch and clean technique is not yet up to par
Main Focus
The main focus of Weeks 10-12 is lifting close to your one rep max (stay within 9-9.5 RPE), being explosive in your power movements (medicine ball slams, jumps, sprints) and anaerobic conditioning
Final Points
Because there is at least one day of Olympic weightlifting exercises in each week of the program, athletes do not have to worry much about losing their athletic ability while trying to build muscle
The periodization (sets x reps over the span of the 12 weeks) provided in the program is rough and very general. Feel free to change training variables to fit your priorities/goals.
The main focus of this program is the training split and phases.
Exercises can be substituted in but try to stick with the main themes of each day (training-split)
Again this program is not intended for beginner-lifters. Some experience with barbell and resistance training is recommended.
A high volume block transitioning to a higher frequency block is a concept I've taken from block periodization an a concept I've used from Greg Nuckol's newest hypertrophy article "Grow Like a New Lifter Again"
PROS
Lots of variation in exercise selection, useful for program adherence and training many different movement patterns
Higher frequency of compound lifts will be beneficial for muscle hypertrophy and strengthening of the nervous system
Speed of exercise execution varies, wide variety of exercise tempo (Eccentrics, pauses, explosive/power movements)
Rest days are strategically placed to improve performance and to fit the stimulus-recovery curves of each movement/muscles
CONS
This is a GENERAL program for size and athleticism and like all general programs, this program may not fit the needs of all sports.
Olympic lifting movements are not trained frequent enough in this program so do not expect large improvements in form. Lifters looking for a program to specifically improve their Olympic weightlifting should look elsewhere. Here are some to get you started: Catalyst Athletics - Breaking Muscle - Pendlay - Russian Approach (via All Things Gym) - Dan John
Although this program does include the powerlifts (big 3 compound exercises), it does not prepare you for a powerlifting competition. Lifters looking for a powerlifting-specific program should look elsewhere. Here are some to get you started: GC Strength & Conditioning Individualized 12-Week Program & Coaching - Candito Training HQ - Sheiko Powerlifting Programs (via Joe Skopec) - Connor Lutz Training Template - Juggernaut Method - 5/3/1 - Cube Method.
Be mindful of comments added to exercises (indicated by a red triangle in the top right of an excel block). They contain useful information about the particular exercise.