Case Study: Blended Training and the Delivery-Limited CrossFit Athlete
Today’s post is a case study from Paradigm Shift: Rethinking Human Performance (Chapter 7: Training Interventions For Delivery Limited Athletes). In this chapter I cover the physiology underlying delivery limitations as well as practical strategies and tools I use to address this limiter profile (from tier one EST to blended sessions, mixed-modal work, and more). The chapter then closes with the case study featured below.
Case Study: Blended Training and the Delivery-Limited CrossFit Athlete
A Games-level female CrossFit athlete came to me in the off-season following a finish that had left her frustrated. On paper, her results were respectable–she had made the Games and competed at the individual level, which puts her in a category that represents a fraction of a percent of all CrossFit athletes globally. But she knew that her finishes on longer conditioning pieces were costing her the overall placement she was capable of. On shorter, more explosive workouts she was competitive with anyone in the field. On anything that demanded sustained output across five or more minutes of mixed-modal work, she was bleeding time.
Her strength numbers were exceptional. Her gymnastics capacity in isolation was among the best in the field. She could string together large unbroken sets of chest-to-bar pull-ups, toes-to-bar, and bar muscle-ups when fresh with minimal drop-off across sets in a controlled environment. But in competition, when those movements were embedded in longer workouts alongside barbell cycling and monostructural cardio, her capacity to sustain unbroken sets collapsed faster than her skill level should have allowed. Competitors she was stronger than and more technically proficient than were finishing ahead of her on those workouts and that gap was costing her in the overall standings.
Physiological testing confirmed what I had suspected from watching her compete. She was delivery-limited. Her oxygen extraction was excellent–her muscles had the mitochondrial density and capillary development to utilize oxygen efficiently when supply kept pace with demand–but the problem was that her maximal cardiac output was the rate-limiting factor, constraining her ability to sustain peripheral blood flow across the large and rapidly alternating muscle groups that Games-level metcons demand. This is a physiological profile that shows up with some regularity in elite female CrossFit athletes with a strength and gymnastics-heavy training background. The peripheral machinery is highly developed. But, the central pump hasn’t been trained with enough specificity to match it.
Her training history told a clear story. The bulk of her conditioning work had been competition-simulation metcons at high intensity, supplemented with heavy strength training and skill work. She had very little structured aerobic base work, and what aerobic training existed in her program had never been prescribed with the intentionality needed to address a delivery limitation. She had been training hard for years. But the stimulus had never been targeted at her actual ceiling.
The first thing we addressed was breathing. Under fatigue, she had a well-ingrained habit of breath-holding during barbell cycling, specifically during heavy thrusters and power cleans, and of breathing shallowly during gymnastics movements to maintain tension. Both patterns were suppressing her venous return and, consequently, her cardiac output at exactly the moments in a workout when she needed it most. We spent multiple sessions doing nothing but drilling breathing mechanics under load: full exhales at the top of thrusters, deliberate inhales on the downswing of pull-up-based movements, and nasal breathing during monostructural work at sub-maximal intensities. The improvement in her ability to sustain output in longer sets was noticeable within the first week, before we had changed a single thing about her training volume or intensity.
Once her breathing mechanics were solid, we built her tier one delivery work. She had essentially skipped this phase of development entirely in her training career, and the foundation needed to be established before tier two interventions would be effective. We introduced D2 and D3 sessions–structured cyclical work on the Echo Bike, rower, and SkiErg–prescribed using SmO2 targets rather than pace or power outputs, since her cardiac output limitation meant that standard pace-based prescriptions would consistently push her out of the intended training zone. She found this phase mentally challenging. Athletes at her level are conditioned to associate productive training with high intensity, and sessions where the goal was to hold SmO2 between forty and sixty percent at a power output well below her competition pace felt counterintuitive. Biometric monitoring was essential here–it gave her objective confirmation that she was generating a meaningful training stimulus even at outputs that felt uncomfortable in their restraint.
After a few weeks of foundational delivery work, we introduced blended intervals. Rather than prescribing fixed-pace Echo Bike or rowing intervals at her competition output, which, as testing had confirmed, would push her oxygen utilization past her supply capacity within the first sixty seconds, we used a progressive build structure. Each interval began at approximately 60% of her maximal sustainable output and built steadily across the work bout to approximately 85–90%, with the average output across the interval matching what a fixed-pace prescription would have produced. NIRS monitoring confirmed the intended effect: an inverse-linear correlation between SmO2 and total hemoglobin across each interval, indicating that oxygen supply and demand were remaining coupled throughout, rather than the occlusion-driven deoxygenation that her fixed-pace intervals had always produced.
We then introduced mixed-modal blended sessions specifically designed to stress the cardiovascular demand that Games competition actually imposes–rapid redistribution of cardiac output between alternating upper and lower body muscle groups under sustained systemic demand. A representative session looked like this: a three-minute Echo Bike build from 60–85% of her heart rate maximum, flowing directly into an unbroken sequence of chest-to-bar pull-ups, thrusters, and toes-to-bar, back to the bike, repeated for four to five sets with structured rest. The order of movements was rotated each set to prevent adaptation to a fixed redistribution pattern. The prescription was not to go as hard as possible–it was to move as continuously as possible while keeping SmO2 from bottoming out before the set was complete. For an athlete accustomed to redlining every conditioning session, this required a significant recalibration of what productive training felt like.
After a few months, the results were unambiguous. Her performance on longer metcons in competition simulation had improved substantially, and the nature of that improvement was qualitatively different from what fitness gains typically look like. She wasn’t just completing more reps. She was completing them more continuously, with shorter transitions, smaller breaks, and a steadier physiological profile from start to finish. Her SmO2 trends during competition-simulation workouts showed the near-linear desaturation pattern that characterizes athletes who can turn metcons into cyclical work, rather than the jagged dips and incomplete recoveries that had defined her earlier testing. Her estimated maximal cardiac output, assessed via the VO2-SmO2 relationship during progressive testing, had improved measurably. On workouts lasting five minutes or longer in the following competitive season, her finishes relative to the field improved significantly compared to the prior year.
The broader lesson this case illustrates is one that is easy to overlook at the Games level, where every athlete is exceptionally fit and the margins are small. At that level, athletes and coaches often assume that the training process has been thorough enough to have addressed all major physiological limitations. In many cases it hasn’t. Not because the training wasn’t hard, but because hardness and specificity are not the same thing. This athlete had trained extraordinarily hard for years. What she had never done was train with enough precision at the right intensity, in the right structure, to give her cardiovascular system a targeted reason to expand its ceiling. Once we did that, the fitness she had already built had a better engine to run on.