Professional Baseball Strength & Conditioning


4 Pillars of In-Season Training

By Brennan Mickelson MS, RSCC, Seattle Mariners

  1. Player development comes first. This is the number one non-negotiable pillar on the list because it encompasses all the other aspects in a broad sense. Each player that you work with has the same goal, to be the best version of themselves. Every athlete will have a different ‘best version’ and the path to get to this will be unique. If an athlete is lacking a fundamental component (i.e., arm speed for throwing velocity or bat speed for exit velocity) improving these components is paramount. However, if the athlete is adequate in these areas improving them is no longer essential. While improvement is great, aggressively investing adaptation currency on attributes in which an athlete is adequate or above average is not necessary and improving ability on field takes precedence.


Working with a high-end prospect who checks all the boxes is not like working with a developmental prospect at risk being to be cut if he/she doesn’t improve throwing velocity or improve bat speed. I would argue the prospect needs to invest his time on maintaining fitness and limiting fatigue so that he/she can play every game and show off his talent. While the developmental player needs to aggressively invest much of their adaptation currency on improving their outputs. This scenario can lead to a fitness and fatigue problem that strength coaches must balance.

  1. Monitor and manage stressors and fatigue. The fitness vs. fatigue conundrum is one that every strength coach is familiar with. There are hundreds of permutations. The simplest explanation is this. Fatigue builds fitness, and at a certain tipping point, too much fatigue inhibits fitness. Paradoxically, a lack of fatigue also inhibits fitness. Finding the “goldilocks zone” of fatigue vs. fitness is the challenge.

“If your athletes’ outputs are improving on the field but the outputs in the weight room are trending down, are you or are you not improving the development of your athletes?”

The simplest answer is you are improving their development. We fatigue athletes with the goal of improving fitness and on-field measures. Our measures in the weight room (especially in season) take a back seat to measures that have stronger correlations to positive outcomes on the field. I will concede that improving strength, power, and speed will always be what we look for as strength coaches. Our job is to make general improvements (mobility, stability, work capacity, strength, power, etc.) with the goal of helping bridge the gap between the weight room and the field of play. If an athlete’s bat speed is improving but their squat jump power is trending down, should we care as a strength coach? Sure, we can care, we can try to limit the magnitude of decrease in fitness with small changes to the stresses we place on the athletes. However, obsessing over the trend and overhauling the athlete’s training plan to improve this measure is a bad idea. In-season training is a delicate balance between fatigue and fitness and how (ambitiously or cautiously) we invest adaptation currency.

  1. Compliment development don’t compete. As touched on earlier, each athlete has their own development plan. As strength coaches, we should complement this plan, not compete against it. This is critical because WE have complete control over the stress that the WE place on the athletes. In the weight room and in conditioning programs, we prescribe the volume, intensity of effort. We understand how each will affect each athlete and consistently adjust them based on observed external factors. Improving the developmental prospects outputs means we need to complement his/her training by ambitiously investing the available adaptation currency with maximal, tolerable doses of stressors that have a higher transfer rate to sport specific movements. Simply put, we need to maximize fatigue while not limiting fitness. With the high-end prospect, we need to be more cautious with investing adaptation currency and focus more on minimal effective doses of stressors to maintain fitness and limit fatigue so he can perform at the highest level each game.

  1. Consistency wins. Like with anything in life, the trajectory is never linear and there are always peaks and valleys. Ensuring the all parties (player, coaches, coordinators) understand the developmental plan is critical. Everyone needs to row in the same direction at the same time. Transparency with where the athlete is at and where they need to be is crucial for effective development. Athletes need to understand why their goals are THEIRS, and why they may need to invest their adaptation currency more aggressively in certain areas than others. Consistency will look different from player to player but consistency will help development players become prospects and prospects become big leaguers.


Brennan Mickelson MS, CSCS, RSCC, is a Minor League Strength Coach for the Seattle Mariners.


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