The radar gun doesn't lie, but sometimes it doesn't tell you much either. A high school pitcher stands on the mound, throws a bullpen, and the coach walks away satisfied because the numbers look fine. Velocity's there. Command's decent. Nothing hurts. But six weeks into the season, that same pitcher has lost a mile per hour, his mechanics are just not syncing, and he's compensating in ways he doesn't even recognize yet. What happened? He trained in the off-season. He threw his bullpens. He did his arm care. And yet, somewhere between January and April, the qualities that drive performance, strength, power, coordination, started to erode. Not because he wasn't working, but because in-season training either disappeared entirely or defaulted to maintenance mode, the kind of programming that keeps you moving but doesn't actually keep you sharp.

A 2024 study published in the Journal of Medical Science Monitor tested a different idea. What if in-season training wasn't about maintenance at all? What if it was about strategic, intentional development, even during the grind of a competitive season? Researchers compared three training protocols in 30 high school pitchers over four weeks: plyometric training, kettlebell training, and compound training, which combined both plyometrics and resistance work. All three groups trained twice per week. All three groups improved in strength, jump height, dynamic stability, and velocity. But the compound training group didn't just improve, they dominated. Velocity increased by 5.9 kilometers per hour, roughly 3.7 miles per hour. Leg extension torque rose by 31.1 Newton-meters, compared to just 8.3 in the plyometric group and 4.3 in the kettlebell group. Y-balance scores improved by over six centimeters on both left and right sides. And all of this happened without adding training days, without piling on volume, and without disrupting the competitive season. The compound training group didn't work more. They worked smarter. And that distinction matters.

You Can't Out-Isolate a System Problem

The plyometric group jumped. The kettlebell group lifted. Both got better. But neither group came close to the compound training group's results. Why? Because pitching isn't a plyometric sport, and it's not a strength sport. It's both. The delivery demands explosive lower body power to generate force through the drive leg and stride leg. It requires rotational strength through the hips and trunk to transfer that force efficiently. It needs postural stability to maintain control across dynamic movement patterns. And it asks the nervous system to coordinate all of these qualities in sequence, under fatigue, pitch after pitch, inning after inning. Training one quality in isolation might move the needle slightly, but it doesn't prepare the system to do what it actually has to do on the mound, integrate multiple physical demands simultaneously.

To be honest, this reminds me of the way most in-season training is structured. Pitchers lift on Monday. Maybe they do some light plyos on Wednesday. Arm care gets squeezed in before games. Everything stays in its own lane. Strength work doesn't talk to power work. Power work doesn't connect to throwing. And no one asks whether the sum of these isolated interventions is actually building the qualities that drive performance. The compound training group in this study didn't just combine plyometrics and resistance training for the sake of variety. They combined them because the adaptations those methods produce, explosive power from plyometrics, structural strength and force production capacity from resistance training, are synergistic. One amplifies the other. Plyometrics teach the nervous system to produce force rapidly. Resistance training gives the muscles and connective tissues the capacity to handle that force under load. Together, they create an athlete who can generate power, stabilize it, and repeat it. Separately, they create incomplete adaptations that don't transfer as effectively to the demands of pitching.

We know from other research that power-based adaptations depend on high-quality, high-velocity repetitions. A 2023 systematic review and meta-analysis on velocity loss thresholds during resistance training found that while strength gains were consistent across all levels of fatigue, power output declined significantly when velocity loss exceeded 25 percent. Every 10 percent rise in velocity loss boosted hypertrophy, but power dropped by up to 4 percent. For baseball athletes, that tradeoff is critical. Pitchers and hitters don't need maximum hypertrophy during the season. They need to move fast, often, and under fatigue. Excessive fatigue blunts explosive output and delays recovery, exactly the opposite of what an in-season athlete needs. The compound training group in the high school pitcher study didn't just train harder. They trained in a way that preserved power output while still building strength, a balance that plyometrics alone or resistance training alone couldn't achieve.

There's also evidence that combining interventions produces synergistic effects that exceed the sum of their individual contributions. A 2025 study on combined caffeine and Rhodiola rosea supplementation in volleyball athletes found that while caffeine alone and Rhodiola alone provided minimal benefit, the combination produced measurable improvements in both explosive power and fatigue tolerance. Athletes in the combined group sustained significantly higher jump heights across 20 consecutive vertical jumps, showing both greater explosiveness and better fatigue resistance. The synergy came from pairing central nervous system stimulation with improved mitochondrial function, two mechanisms that amplify each other when combined. The compound training group in the pitcher study likely benefited from a similar principle. Plyometrics stimulate the nervous system and improve rate of force development. Resistance training builds the structural capacity to produce force under load. Together, they create adaptations that neither method produces in isolation.

The Qualities That Drive Velocity Start Below the Waist

One of the most striking findings in this study was the magnitude of strength gains in the compound training group. Leg extension torque increased by over 30 Newton-meters, more than three times the gains seen in the plyometric group and more than seven times the gains in the kettlebell group. That's not a subtle difference. That's a different training effect entirely. And while leg extension torque might sound like a gym metric that doesn't matter on the mound, we know from research that lower body power is one of the strongest predictors of throwing velocity. A 2025 study on youth baseball hitting performance found that standing broad jump distance was the strongest predictor of batted ball velocity, even after controlling for height and weight. Each four-inch increase in broad jump distance was associated with a 1.4 mile-per-hour increase in batted ball velocity. The principle is the same for pitching. Lower body power drives velocity. The legs generate force. The trunk transfers it. The arm receives it. If the foundation isn't strong, the rest of the kinetic chain compensates. And compensation, over time, leads to inefficiency, fatigue, and injury.

The compound training group didn't just get stronger. Their movement patterns became more stable and controlled. Y-balance scores improved by over six centimeters on both the left and right sides, roughly double the improvements seen in the plyometric and kettlebell groups. Dynamic stability isn't just about standing on one leg without falling over. It's about controlling the body's center of mass during dynamic movement, maintaining postural control under rotational demands, and coordinating multiple joints and segments in sequence. Pitchers who can't stabilize through the drive leg or control their pelvis during hip-to-shoulder separation are asking their arms to absorb forces that should have been managed further down the chain. The compound training group built the strength and coordination to control those forces. The other groups didn't, at least not to the same degree.

Two Sessions Per Week Was Enough

One of the most important details in this study is what didn't happen. The compound training group didn't train more than the other groups. They didn't add extra sessions. They didn't increase volume. They trained twice per week, just like everyone else. And yet, they improved significantly more across every metric. That suggests the issue isn't always about doing more. It's about doing the right things in combination. In-season training is constrained by time, fatigue, and competition demands. Athletes can't afford to spend five days a week in the weight room. But they also can't afford to let the qualities that drive performance erode over the course of a season. The compound training group found a middle path. They trained just enough, with the right combination of stimuli, to not only maintain performance but improve it.

We also know from research on training frequency that even minimal training stimulus can slow the decay of adaptations, but once training stops entirely, everything fades. A 2024 study on reduced training frequencies after 12 weeks of concurrent resistance and aerobic training found that when all training stopped, strength, muscle size, and aerobic power all returned to baseline within weeks. Even the group that had been training once per week lost nearly all of their adaptations once they stopped completely. For in-season athletes, the message is clear. You don't need to train as hard or as often as you do in the off-season, but you can't stop training entirely. Two sessions per week, structured intelligently, appears to be enough to maintain and even build the qualities that matter. Zero sessions per week is not.

There's also precedent for low-volume, high-impact in-season training in other research. A 2023 study on blood flow restriction training in collegiate pitchers found that adding BFR to low-load rotator cuff exercises, just twice per week over eight weeks, led to significantly greater shoulder mass, strength, and endurance compared to controls. The BFR group gained 227 grams of shoulder mass compared to 75 grams in the control group. Endurance increased by 190 kilograms. And critically, pitching mechanics were preserved. The training didn't disrupt performance. It enhanced it. The compound training group in the high school pitcher study followed a similar principle. Strategic, low-volume interventions, when designed correctly, can produce meaningful adaptations even during the competitive season.

The Big Idea No One Wants to Admit

Most in-season training protocols are built on fear, not strategy. Coaches worry that lifting too heavy will make athletes stiff. They worry that plyometrics will fatigue the legs and mess with mechanics. So they default to maintenance mode, light weights, high reps, low intensity, and hope that nothing breaks. But maintenance mode doesn't maintain anything. It's a slow decline disguised as caution. The compound training group in this study proved that you can train intelligently during the season, build strength, power, and dynamic stability, improve velocity, and do it all without adding training days or disrupting competition schedules. The key isn't avoiding stress. It's applying the right kind of stress, in the right combination, at the right dose.

The lesson here isn't that every in-season program should copy this exact protocol. The specific exercises used in this study, the kettlebell swings, the depth jumps, the resistance patterns, might not fit every athlete or every context. But the principle is universal. Combining resistance training and plyometrics produces synergistic adaptations that exceed what either method produces alone. Training twice per week is enough, if the programming is intentional. And in-season development isn't just possible, it might be necessary if you want athletes to finish the season stronger than they started.

References

Kim J, Jaber H, Yim J. Comparison of the Effects of Compound Training, Plyometric Exercises, and Kettlebell Exercises on Strength, Power, Dynamic Balance, and Pitched Ball Velocity in 30 Male High School Baseball Pitchers Aged 16-19 Years. Int J Med Sci Monit. 2024. PMID: 39118306.

Jukic I, Pérez Castilla A, García Ramos A, et al. The Acute and Chronic Effects of Implementing Velocity Loss Thresholds During Resistance Training: A Systematic Review, Meta-Analysis, and Critical Evaluation of the Literature. J Sports Med. 2025. PMID: 36178597.

Tao B, Sun H, Li H, et al. Combined Effects of Rhodiola Rosea and Caffeine Supplementation on Straight Punch Explosive Power in Untrained and Trained Boxing Volunteers: A Synergistic Approach. Metabolites. 2025. PMID: 40278391.

Bordelon NM, Agee TW, Wasserberger KW, et al. Field-Testing Measures Related to Youth Baseball Hitting Performance. J Strength Cond Res. 2025. PMID: 39874526.

Lambert BS, Hedt C, Ankersen JP, et al. Rotator Cuff Training with Upper Extremity Blood Flow Restriction Produces Favorable Adaptations in Division IA Collegiate Pitchers: A Randomized Trial. J Shoulder Elbow Surg. 2023. PMID: 36933646.

Mpampoulis T, Stasinaki AN, Methenitis S, et al. Effect of Different Reduced Training Frequencies after 12 Weeks of Concurrent Resistance and Aerobic Training on Muscle Strength and Morphology. J Sports (Switzerland). 2024. PMID: 39058089.