Abdominal bracing, core strength & teaching irradiation
The role of the abdominal musculature on bracing and improving spinal stability is well established in the literature through the work of Stu McGill (seen here, and here). This paper by Tayashiki et al is the first research paper to investigate whether or not maximal abdominal bracing training has an impact on trunk and lower limb power and strength outputs.
Can maximal voluntary contraction of abdominal muscles (abdominal bracing) training improve strength and power output of the trunk and lower limb muscles?
The research team split a 20 person subject pool into a training group (TG n=11) and a control group (CG n=9). The training group underwent an 8-week program that had them training 3 times per week. The group would perform 2s of maximal abdominal bracing, followed by 2s of relaxation for 5 reps 10 times per day. There was a 2 minute interval between sets.
All subjects reported being active in their daily life and participating in recreational sports (>30min, >2x per week). Abdominal muscle thickness, muscle strength, maximal lifting power from a sitting position, surface electromyograms (EMGs) of trunk and lower limb muscles, and maximum internal abdominal pressure (IAPmax) were determined before and after the 8-week intervention.
What did they find? :
- A significant increase in isometric trunk and hip extension strength as well as maximal lifting power was seen in the training group, while no changes in strength or power were seen in the control group
- Muscle thickness of the internal oblique, and the maximal intra-abdominal pressure (IAPmax) increased significantly for the training group but not the control group.
Author’s Key Takeaway:
A training program that includes maximum co-contraction of the abdominal muscles can be a modality to improve strength and power generation capability during trunk and hip extensions without the use of external loads.
Potential limitations: this study only investigated the effects on recreational athletes, and not elite or sub-elite athletes. It is very plausible that there would be less of an effect on athletes who are playing at a higher level, and therefore training with more rigor and likely resistance training, than those who are recreational. Further, it did not look at age effects, with both the training and control groups being the same age. My suspicion is that this would not play as important of a role as the training level of the athletes in question.
The bottom line is that training abdominal bracing in athletes can (likely) improve trunk muscle strength and power; however, several questions still remain unanswered. What is the effect of increased trunk muscle strength and power on athletic performance measures? What is the effect when looking at elite-athletes, when compared to novice or recreational athletes? Is there an optimal way to train abdominal bracing? What is the effect if simultaneously training trunk and lower limb strength?
While some of these questions do not yet have a definitive answer, I will attempt to shed some light by sharing our thought processes on some of these scenarios.
Purpose: to quantify associations between variables of trunk muscle strength (TMS), physical fitness and athletic performance and the effects of core strength training (CST) on these measures in healthy individuals.
The core is important in creating proximal stability for distal mobility.
According to Akuthota et al.,
the “core refers to the muscular box consisting of the abdominals in the front, paraspinals and gluteals in the back, the diaphragm as the roof, and the pelvic floor and hip girdle muscles as the bottom”.
Main takeaways from the discussion:
- CST resulted in large effects in TMS, but predominantly small effects in physical fitness and athletic performance when compared with no or only regular training, and overall small effects when compared with alternative training.
- Small-sized effects of CST on physical fitness and athletic performance outcomes were not affected by the athletes’ expertise level (i.e., elite, sub-elite, recreational).
- Regarding expertise level (recreational athletes vs elite and sub-elite athletes), there was a significantly larger correlation between TMS and muscle strength in the recreational athletes (mean r = 0.49) compared with elite (mean r = 0.08) and sub-elite (mean r = 0.07) athletes.
Let’s break this down a bit. First, that CST had a large effect on TMS, but small effects on physical fitness and athletic performance. Physical fitness was predominantly described as strength, power, and balance, whereas athletic performance more aligned with sport related outcome times (kayaking times, 5000 m run times, etc).
Findings from this meta-analysis suggest that TMS plays an insignificant role in athletic performance and physical fitness in general. The athletes with higher TMS scores were not necessarily those that had the highest performance measures. Part of this could be that TMS assessment tests commonly reflected submaximal actions (like core endurance) vs maximal or explosive (jumping, throwing), but there is likely another explanation, which is argued below.
The authors point to the work of Clayton et al., who reported “small-sized associations between peak torque of the trunk flexors/extensors and vertical countermovement jump height (-0.18 \\r\\0.10) in collegiate baseball players (20 ± 2 years)”.
Based on this the authors suggest that performance likely has more to do with well-timed activation of agonistic and synergistic muscle groups, and not maximal trunk muscle activation.
In other words, the role of the core “is rather a matter of quality (i.e., intermuscular coordination) than of quantity of trunk muscle activation/force production during movement tasks”.
This coordination idea is further supported by the work of Chaudhari et al., which demonstrated that “better lumbopelvic control during single leg stance tasks as a measure of intermuscular coordination was associated with higher in-game pitching performance in professional baseball players (23 ± 2 years)”. This really shouldn’t come as a shock, as athletic function and coordination have been linked in the literature several times (here, and here).
This brings us to the second point, regarding player expertise (recreational vs sub-elite and elite), which found very small correlations between CST and performance. Here, again, we can point to the lack of connection established between TMS and performance. Elite players might not have high levels of TMS, and vice versa. There are recreational players who exhibit large TMS measures. This adds to the argument that sequencing and coordination play a greater role than pure strength.
For the basis of our argument, substitute novice for recreational, and experienced for elite when dissecting the third point (significantly larger correlation between TMS and muscle strength in the recreational athletes (mean r = 0.49) compared with elite (mean r = 0.08) and sub-elite (mean r = 0.07) athletes).
If we look at this from a training progression standpoint, novice lifters are typically given a more general or basic strength program, whereas experienced lifters train with more specific (sport-specific, power-based, plyometric training) or complex programs. The latter of which may lead to increased sport-specific strength in the sport-specific limbs.
Athletes with higher limb muscle strength often do not have higher levels of TMS, since they already have a solid base on which to become more specialized.
Core muscle strength vs abdominal bracing: is there a difference, or are they one and the same?
Core strength training in the context of the meta-analysis refers to training of these (abdominals in the front, paraspinals and gluteals in the back, the diaphragm as the roof, and the pelvic floor and hip girdle muscles as the bottom) muscle groups. All of them must be involved, not just one set. To be more specific, core strengthening exercises of the included training studies were preferentially performed under isometric conditions and/or in vertical directions while lying in horizontal positions with various sets and reps (e.g., prone planks, crunches).
The major difference would be the position in which they were trained, and whether or not IAP was measured using EMG or intra-rectal pressure transducers. While CST studied in the review typically involved horizontal positioning and EMG, abdominal bracing training was performed seated, in lumbar neutral with intra-rectal pressure transducers.
Regardless of this, both the RCT and the meta-analysis informed us of the same thing: abdominal bracing training/core strength training can improve maximal trunk strength and power outputs.
The question remains, however, whether abdominal bracing is important in athletic performance?
Although it’s effect on TMS might not be, our stance is that training abdominal bracing in a coordinated, structured fashion acts as a prerequisite upon which we can build more dynamic, coordinated, and purposeful movements.
This is part of the reason we stress the importance of proper bracing technique (for more on how we describe this, keep reading) in all of our athletes, and near the beginning of our training programs for our novice athletes. It serves as a foundation on which we continue to build more complex movements and advanced strength.
How do we teach abdominal bracing, and core muscle strength?
Bressel et al. showed that “verbal instruction is even more effective to increase trunk muscle activation during lower limb resistance exercises (i.e., squats) as compared with higher training loads in resistance-trained males”. Appropriate instructions could thus play an important role as a prerequisite for creating sufficient and adequate core strength.
Proper education and instruction plays a vital role in how we go about our training.
We start with a description of the abdominal cavity, which is almost identical to the definition by Akuthota above (the “core refers to the muscular box consisting of the abdominals in the front, paraspinals and gluteals in the back, the diaphragm as the roof, and the pelvic floor and hip girdle muscles as the bottom”).
But, we know our audience.
This is usually a bit much for 13-16 year old boys to grasp or care about, which typically leads to a more simple description of “the canister, or coffee can”.
One of the main ways we develop the activity of abdominal bracing in our novice athletes is during our practice of controlled articular rotations (CARs), progressive angular isometric loads (PAILs) and regressive angular isometric loads (RAILs); which we use to explore, maintain, and improve range of motion in our athletes joints. We use the concept of “irradiation” to help teach and train these exercises.
Irradiation (also termed ‘the law of irradiation’) originates from Sir Charles Sherrington, who is also responsible for the Sherrington Law of reciprocal inhibition (for more on this, see here). According to the Law of Irradiation: “A muscle working hard recruits the neighbouring muscles, and if they are already part of the action, it amplifies their strength. The neural impulses emitted by the contracting muscle reach other muscles and ‘turn them on’ as an electric current starts a motor..”
Where does this leave us?
We now know that you can both teach and train abdominal bracing and core strength, and increased maximal abdominal strength can likely improve trunk muscle strength. We also know that greater measures of trunk muscle strength likely has a very small role in athletic performance. As was talked about, however, there is a valuable role to played in properly training the “core” to act as a prerequisite upon which to expand our movement profiles.
Akuthota, V., Ferreiro, A., Moore, T., & Fredericson, M. (2008). Core Stability Exercise Principles. Current Sports Medicine Reports, 7(1), 39-44. doi: 10.1097/01.csmr.0000308663.13278.69
Bressel E, Willardson JM, Thompson B, et al. Effect of instruction, surface stability, and load intensity on trunk muscle activity. J Electromyogr Kinesiol. 2009;19(6):e500–4.
Chaudhari AMW, McKenzie CS, Borchers JR, et al. Lumbopelvic control and pitching performance of professional baseball pitchers. J Strength Cond Res. 2011;25(8):2127–32.
Clayton MA, Trudo CE, Laubach LL, et al. Relationships between isokinetic core strength and field based athletic performance tests in male collegiate baseball players. J Exerc Physiol. 2011;14(5):20–30.
Hodges PW, Richardson CA. Contraction of the abdominal muscles associated with movement of the lower limb. Phys Ther. 1997;77(2):132–42.
Kibler WB, Press J, Sciascia A. The role of core stability in athletic function. Sports Med. 2006;36(3):189–98.
Prieske, O., Muehlbauer, T., & Granacher, U. (2015). The Role of Trunk Muscle Strength for Physical Fitness and Athletic Performance in Trained Individuals: A Systematic Review and Meta-Analysis. Sports Medicine, 46(3), 401-419. doi: 10.1007/s40279-015-0426-4
Tayashiki, K., Maeo, S., Usui, S., Miyamoto, N., & Kanehisa, H. (2016). Effect of abdominal bracing training on strength and power of trunk and lower limb muscles. European Journal Of Applied Physiology, 116(9), 1703-1713. doi: 10.1007/s00421-016-3424-9