Reviewed by John Baur, PT, DPT, OCS, CSCS, FAAOMPT

This article explains why and how to use “flywheel eccentric training” to deliberately create eccentric overload—loads greater than what the athlete can produce concentrically—and provides practical programming, safety, and exercise‑selection guidance for sport performance and injury prevention. Eccentric contractions are the active “lengthening” of muscle and are unique in several ways: eccentric strength is ~40% greater than concentric strength; force rises with velocity until it plateaus; the metabolic cost and motor unit recruitment are lower for a given mechanical output; and a phenomenon called residual force enhancement (likely involving titin) can elevate force after lengthening. Together, these neuromuscular and mechanical features make eccentrics especially potent for strength, speed, change of direction (COD), and resilience to injury.

Muscle damage, DOMS, and the repeated‑bout effect. Eccentrics can induce more muscle damage when loads are higher, velocities faster, muscle lengths longer, or individuals are inexperienced; genetics matter too. However, damage is not “inevitable”—unaccustomedness is a major driver—and the repeated‑bout effect rapidly reduces soreness and damage on subsequent exposures. Practically, coaches should progress volume, intensity, and exercise length appropriately, especially when training at long muscle lengths that, while beneficial for adaptations, also heighten DOMS.

What adaptations do eccentrics drive? Compared with concentric work, eccentric training tends to produce larger gains in maximal strength and distinct morphological changes: increased fascicle length, greater serial sarcomere number, region‑specific hypertrophy, lower pennation angle, and increased stiffness. These adaptations underpin stronger sprinting, jumping, stretch‑shortening cycle efficiency, and faster COD—partly by enabling greater braking and propulsive forces with shorter contact times. Meta‑analyses cited in the paper show improved speed, power/jump, and COD performance after eccentric‑biased or flywheel programs.

Why eccentrics are especially relevant in team and racket sports. Match analyses show team sports often involve more and/or more intense decelerations than accelerations, making the ability to absorb force a key determinant of performance and fatigue. For example, in soccer, harsher CODs are linked with neuromuscular fatigue, and the most common goal‑preceding movements include linear advances followed by decelerations and turns. A controlled trial in U23 women’s soccer reported that 10 sessions of lower‑body flywheel eccentric work increased high‑intensity accelerating/decelerating distance and peak/average acceleration–deceleration versus controls, supporting real‑match relevance.

How flywheel devices work and why they’re useful. A flywheel system stores kinetic energy during the concentric phase and returns that inertia to the user in the subsequent eccentric phase, enabling mechanical eccentric overload if programmed correctly. The device is portable, accommodates resistance through the full ROM (no “sticking point”), and lets athletes perform multi‑planar, sport‑specific patterns. Device geometry matters: “horizontal, cylinder‑style” systems generally afford higher eccentric forces, whereas “vertical cone” (“conical pulley”) systems can reach higher velocities. Low inertias behave like light loads (emphasizing velocity and SSC use), high inertias like heavy loads (emphasizing force). The intent is maximal speed in the concentric phase and decisive braking in the eccentric phase. Figure 1 (p. 6) in the article illustrates common devices (squat, leg curl/extension, leg press, pulley, conical pulley, multigym).

Training effects of flywheel eccentric training. Systematic reviews and meta‑analyses highlighted by the author indicate increases in strength, power, sprint speed, and COD, often surpassing gravity‑dependent controls; some umbrella reviews note similar outcomes to traditional resistance training, but overall the weight of evidence is favorable—particularly among younger and well‑trained athletes who “attack” both concentric and eccentric phases. Flywheel eccentric work has also been linked to fewer in‑season injuries in team sport cohorts, potentially via increases in hamstring fascicle length.

Programming guidelines. The paper synthesizes practical guidance (Table 1, p. 8–9):

Power: 2 + 3–6 reps, 1–3 sets, low–medium inertia, short rests; devices like conical pulley/flywheel pulley/squat.

Strength: 2 + 5–8 reps, 1–4 sets, medium–high inertia, longer rests; devices like squat, multigym, leg press, extensions/curls.

Injury prevention: 2 + 5–8 reps, 1–4 sets, low–to–high inertia depending on exercise selection (single‑joint often preferred).

The “2 + x” notation means 2 start‑up “spin‑up” reps to accelerate the wheel, then x maximal reps. Recommended frequency is 1–3 sessions/wk (≥48 h between), with higher inertias requiring more rest between sets.

Weekly scheduling. The author outlines in‑season and two‑match‑week templates (Tables 2–3, pp. 9–10). A common structure is a power session on MD‑4, an upper‑body + microdose lower‑body strength/IP later that day, and a main lower‑body strength/IP on MD‑3, with adjustments for starters vs non‑starters and microdoses after midweek matches when congested. The aim is to maintain strength/IP stimuli without compromising freshness for matches.

Eccentric overload is not automatic. A key caution: only 17 of 79 flywheel studies provided enough data to confirm actual eccentric overload, typically via higher eccentric “peak” power/velocity than concentric. Reasons overload may be absent include submaximal concentric intent (insufficient stored energy), movement mechanics (e.g., peak concentric force in stronger joint angles vs peak eccentric near the turning point), and inexperience. Overload likelihood rises with horizontal cylinder devices, higher inertias, technique that “reduces eccentric time” (e.g., braking in the final third), and user experience. The paper also notes possible gender and experience influences.

Methods to “create” eccentric overload (Figure 3 and photo sequences in Figure 4, pp. 12–14).

1. Increase concentric ROM (e.g., add plantarflexion or a late hip rotation) so more energy is generated concentrically than will be absorbed eccentrically.
2. Reduce eccentric ROM/time (alternate half/quarter squats; stop the wheel in the last third; or perform a high‑overload “catch,” i.e., attempt an isometric hold low, then yield).
3. Coach/athlete/load‑assisted (assist concentric to create more stored energy; assist eccentric by pulling the rope down; or add a hand‑held load only during the eccentric phase).
4. Alternate exercises or laterality between phases (e.g., concentric squat → eccentric RDL; or concentric bilateral → eccentric unilateral).
5. Combine methods for advanced athletes (e.g., add rotation “and” brake in the last third). Direct device feedback (encoders/force plates via the manufacturer’s app) is encouraged to verify overload and motivate effort.

Safety, technique, and progression. Start with 1–2 exercises for novices; advanced athletes may tolerate 2–4 exercises × 2–4 sets. Ensure the harness is correctly fitted; on squat devices, teach athletes to “immediately” flex hips/knees after lockout to avoid “hanging” at end‑range; cue stable foot placement mid‑platform; and use the device’s stop to finish safely. A touch of plantarflexion at the top can smooth the transition from concentric to eccentric. Tables 4–6 (pp. 14–16) give full lower‑body session examples for athletes at low, medium, and high flywheel competence, including power primers, microdosing, and strength lifts.

Bottom line. Flywheel devices can reliably deliver eccentric overload “when you design for it”, not merely by using the device. Choose the right inertia and device, emphasize maximal concentric intent, shorten eccentric absorption time or increase concentric energy, progress volume thoughtfully, and place sessions intelligently in the weekly plan. Done well, flywheel eccentrics enhance strength, speed, jump, COD, and may lower injury incidence—especially in sports dominated by decelerations.

1. C. Eccentric. Eccentric = active lengthening where the muscle “absorbs” energy from an external load (p. 3).
2. C. 40%. Eccentric strength is ~40% greater than concentric in men and women (p. 3).
3. A. Increases. Eccentric force increases with higher speeds until it plateaus/slightly decreases (p. 3).
4. B. Greater pennation angle. Eccentrics tend to “lower” pennation angle while increasing fascicle length and sarcomere number (p. 4).
5. A. Increase speed performance. Meta‑analysis shows improved sprint speed after eccentric‑biased training (p.4).
6. C. Inertia. The device returns inertia accumulated in the concentric phase to the eccentric phase (p. 5).
7. A. Light/heavy. Low/high inertia in flywheel work maps to light/heavy load in traditional training (p. 5).
8. A. An increase in muscle fascicle length. Longer fascicles are a plausible mechanism for reduced in‑season injuries observed with flywheel eccentrics (p. 7).
9. C. High inertias. High inertias are recommended for strength adaptations (>0.050 kg·m²) (p. 7).
10. C. High inertias. Researchers (Raya‑González etal.) recommend high inertias for injury prevention (p.7).

References:

Martínez‑Hernández D. Flywheel Eccentric Training: How to Effectively Generate Eccentric Overload. Strength & Conditioning Journal. 2024;46(2):234‑250.

Conor Heffernan traces the barbell back squat from a 19th‑century bodyweight drill to a loaded, multi‑purpose exercise central to strength training. He frames this evolution around three drivers: “equipment changes”, the “diversification of strength sports”, and “scientific communication” about safety and efficacy. Understanding this history, he argues, helps coaches avoid dogma about a single “correct” way to squat and instead program movements that fit a lifter’s goals and context.

Early patterns: gymnastics and “tippy‑toe” squats.

Modern fitness boomed with European gymnastics between 1790 and 1830—especially Jahn’s German “Turnverein” and Ling’s Swedish systems—implemented primarily in schools and militaries. These programs emphasized bodyweight drills; lower‑body work appeared, but the trunk and upper body dominated. Early squat instructions placed lifters “on the balls of the feet”, descending until thighs touched the heels while staying very upright—a technique seen in 19th‑century manuals and still common into the early 20th century.

First load: the dumbbell, then the barbell.

The first significant change was simply adding weight. As mass‑produced dumbbells appeared late in the 19th century, figures like Eugen Sandow popularized light, spring‑grip dumbbells for the public—often used while squatting on tiptoes. Commerce played a crucial role: Sandow marketed “safe” light weights that promised striking physiques, nudging the public toward loaded squats. The next leap came with “adjustable free weights”. Alan Calvert’s Milo Barbell Company (founded 1902) offered dumbbells and barbells that were first loaded with lead shot (metal pellets) and later “iron plates”, laying the foundation for progressive overload. A 1915 Milo pamphlet prescribed high‑rep “deep knee bends” with a “barbell on the back”, still balanced on tiptoes. A key constraint remained: balance—not strength—often limited load.

Modernizing technique: flat‑foot squats and racks.

In the 1920s, lifters began squatting “flat‑footed”, unlocking heavier loads and different muscular demands. Some feats—like H.P. Hansen’s 277‑lb × 65 reps (1899)—suggest earlier flat‑foot use, but broad adoption came later. In Europe, “deep knee bends” were already competitive by the “1910s–1920s”. In the United States, German strongman Henry “Milo” Steinborn became the pivotal evangelist. He not only popularized flat‑foot squatting but also demonstrated a way to get a heavy, unracked bar onto the back by “rocking” it from a vertical start into a deep squat and then standing—an approach widely imitated.

Two figures, Mark Berry and J.C. Hise, accelerated adoption. Berry’s “husky” program paired “high‑rep, heavy squats” (20–40 reps) with the now‑legendary “gallon of milk a day,” while Hise reported rapid weight gain and became a celebrity advocate. Their practical innovations included the “cambered bar” and, critically, early “squat racks/stands”—from boxes and tree branches to purpose‑built devices. By the 1940s, commercial racks (e.g., from York Barbell) were appearing in gyms. With flat feet, heavier loads, and a rack, the elements of the “modern” back squat were in place by mid‑century.

Competition and technology: weightlifting, powerlifting, bodybuilding.

From the 1900s to the 1950s, the strength world revolved around “Olympic weightlifting”. Cold War rivalry led to widespread “anabolic steroid” use after U.S. team physician John Ziegler developed Dianabol (1958), increasing athletes’ capacity and forcing the creation of drug‑tested vs untested federations. Meanwhile, the 1960s birthed “powerlifting”—making the squat a judged “competition lift” (with specific depth rules) rather than just an assistance exercise. This shift catalyzed technique debates (e.g., depth standards) and a wave of “supportive equipment”. Early experiments included “knee bandages”, even “tennis balls halved behind the knees” and “tight bedsheets” for body tension; by the 1970s, dedicated “knee wraps and squat suits” became common, alongside a proliferation of federations with differing equipment policies.

Another 1960s innovation driven by the “isometric craze” was the “power rack”, which enabled “isometric holds” at sticking points and novel partial‑range work. Though the isometric fad waned in the 1970s, the power rack remained a staple—an enabling technology for many squat variations and overload strategies. Footwear also evolved: “heeled weightlifting shoes” (often wooden heels) helped athletes sit deeper with a more upright torso, and later mass‑market models (e.g., Adidas with Tommy Kono) entered both weightlifting and powerlifting. For lifters with limited ankle mobility, such shoes facilitated “fuller range of motion”. In the 2000s, “CrossFit” popularized hybrid shoes, balancing lifting stability with general athletic movement.

“Bodybuilding” surged in the 1970s–80s—familiar to the public via “Pumping Iron”—and further normalized the back squat for “quadriceps hypertrophy” (iconically, Tom Platz). Simultaneously, “weight‑training machines” (e.g., Nautilus, from 1970 onward) entered commercial gyms, lowering user skill requirements and spawning machine‑based “squat” analogues (leg press, Smith machine, pendulum squat). Even where free‑weight back squats weren’t used, “squat‑like patterns” proliferated across the training landscape.

Science, safety, and messaging.

Through much of the early 20th century, heavy lifting met resistance from medicine and sport (fears of “muscle‑bound” athletes abounded). Entrepreneurs like Bob Hoffman and Joe Weider funded content and equipment, and figures such as Thomas DeLorme helped bring “progressive resistance” into rehab. By 1978 the NSCA was founded; soon, strength training became a staple in sport. Yet scientific messaging also “restricted” squatting at times: Karl Klein’s 1961 research asserted that “deep squats” destabilize knees, promoting “parallel/half‑squats” and “knees not past toes” rules. Later work (including an NSCA 1991 position paper) “debunked” his conclusions, but Klein’s influence persisted publicly for decades. More recent position statements confirm the “safety and value” of strength training (and squatting movements) for “youth” and “older adults”, further widening participation.

Practical takeaways

Heffernan closes by urging coaches to prioritize the “movement pattern” over any sacred exercise. The squat’s purpose has always shaped its form—high‑rep mass work vs low‑rep maximal lifts; weightlifting vs powerlifting vs bodybuilding; rehab vs general fitness. History shows “no single universal squat”, only context‑appropriate variations (high‑bar, low‑bar, front, goblet, Zercher, sissy, hack, and more). Recognizing how “commerce, competition, and communication” mold “truths” in training makes practitioners more critical, adaptable, and client‑centered.

1. “b. Gymnastics.” The 19th‑century gymnastics boom (Jahn’s “Turnverein”, Ling’s Swedish system) popularized bodyweight squatting patterns.
2. “b. Dumbbells.” The first big addition was adding weight with dumbbells (popularized by Sandow), before widespread barbell adoption.
3. “a. Metal pellets.” Early adjustable implements were loaded with “lead shot” (metal pellets) before iron plates became standard.
4. “c. 1910s.” “Deep knee bending” was a “competitive” practice in Germany by the “1910s–1920s”.
5. “b. 1960s.” Powerlifting coalesced as a sport in the “1960s” (first national meet in 1964; AAU‑sanctioned meet in 1965).
6. “c. Isometric holds.” The rise of the “power rack” in the 1960s enabled isometric holds and partial‑range work at sticking points.
7. “b. Tennis balls cut in half behind the knees.” Early supportive “hacks” in the 1960s included halved tennis balls and tight bed‑sheet wrapping before modern wraps/suits.
8. “a. Squat with a full range of motion.” Heeled weightlifting shoes helped lifters sit deeper with a more upright torso and assisted those with limited ankle mobility.
9. “c. Iron Game sports.” Weightlifting, powerlifting, and bodybuilding are collectively referred to as “Iron Game” sports.
10. “a. An exercise scientist.” “Karl Klein”, an exercise scientist, popularized joint‑specific safety concerns (arguing against deep squats) that influenced practice for decades.

Reference:

Heffernan C. The history and evolution of the back squat in the United States. Strength Cond J. 2025;47(3):269-278.