Prepubertal Sprint Development: What the Science Says About Isometrics, Loaded Running and Sprint Mechanics

Speed development in children is often oversimplified. Young athletes are frequently given adult sprint drills, heavy resisted sprints or strength exercises under the assumption that greater resistance will automatically produce greater speed.

That assumption is not fully supported by the research.

Before puberty, improvements in sprint performance are influenced by a combination of physical growth, neural development, coordination, strength, impulse production and the ability to direct force into the ground.

Isometric strength training and resisted running may contribute to that process, but neither should replace actual sprinting or become the primary method used to develop running mechanics.

The scientific evidence suggests that prepubertal athletes benefit most from an integrated approach that develops movement competency, relative strength, force control, elastic qualities and frequent exposure to technically sound sprinting.

Prepubertal generally describes a child who has not yet experienced the major hormonal and physical changes associated with puberty. In sports-science research, athletes are often classified according to their position relative to peak height velocity, or PHV.

Peak height velocity refers to the period during adolescence when an athlete experiences their fastest rate of vertical growth.

Researchers commonly classify young athletes as:

• Pre-PHV: before the adolescent growth spurt.

• Circa-PHV: near the period of fastest growth.

• Post-PHV: after the fastest phase of growth.

Prepubertal and pre-PHV are often used as related terms, but they are not identical. Chronological age is also an imperfect indicator of maturation. Two athletes of the same age may differ considerably in height, body mass, hormonal development, strength, coordination and movement capacity.

For this reason, training decisions should not be based on age alone. Maturation status, training experience, movement quality and individual physical development should all be considered.

Sprinting is a highly coordinated expression of force.

To accelerate, an athlete must apply force into the ground in a direction that produces forward movement. The athlete must also organize the trunk, pelvis and limbs while completing each ground contact within a limited period.

Children generally become faster as they grow, but the changes responsible for improved sprinting are not always technical.

Wdowski and colleagues compared physically active boys aged 8–9 with boys aged 11–12 during 15-meter acceleration sprints. The older boys completed the first 5 meters approximately 6.1% faster and the full 15 meters approximately 5.9% faster than the younger group. They also produced greater horizontal and vertical impulse during the first ground contact. (⁠Frontiers)

However, the researchers found no significant overall differences in the joint kinematics of the first sprint stance between the two groups.

The older boys were faster and produced more impulse, but their sprint mechanics had not necessarily developed to the same degree as their physical force capacity. (⁠Frontiers)

This finding is important.

Children do not automatically become technically efficient sprinters simply because they become larger and stronger. Physical development may increase the amount of force available, but athletes must still learn how to apply that force effectively during acceleration.

The study was small and examined only the first stance phase, so its results should not be generalized too broadly.

Maturation was also not directly controlled. Still, it provides useful evidence that increased force production and improved sprint technique do not always develop at the same rate. (⁠Frontiers)

Producing high force in a strength test is not the same as applying force effectively while sprinting.

An athlete may demonstrate good general strength but still struggle to:

• Project the center of mass forward.

• Maintain an appropriate acceleration posture.

• Control pelvic and trunk movement.

• Strike the ground in a useful position.

• Produce force within short ground-contact periods.

• Coordinate the recovery and repositioning of the swing leg.

Research in sprint biomechanics has shown that the direction and effectiveness of force application are important determinants of acceleration. An athlete must not only produce force but direct a meaningful portion of that force horizontally during the acceleration phase. (⁠PubMed)

This does not mean athletes should attempt to consciously push backward during every step.

Sprinting occurs too quickly for excessive internal technical instructions. It means training should create environments in which the athlete learns to project, accelerate and reposition naturally while maintaining effective posture and rhythm.

Strength provides capacity. Sprinting develops the skill of expressing that capacity at speed.

An isometric muscular action occurs when a muscle produces force without a visible change in joint position.

Examples include:

• Holding a split-squat position.

• Pushing against an immovable object.

• Maintaining a calf-raise position.

• Holding the trunk and pelvis against external force.

• Performing an isometric mid-thigh pull.

Sprinting itself is not an isometric activity. The ankle, knee, hip, pelvis and trunk all move during sprinting.

However, certain muscle-tendon units may behave in a relatively stiff or quasi-isometric manner during portions of stance. The athlete must resist excessive joint collapse while transferring force rapidly through the body.

This is where isometric training may be useful.

Isometric exercises can help young athletes learn to create tension, organize joint positions and produce force without the coordination demands of a fast dynamic movement. They can also strengthen specific positions and provide a lower-complexity introduction to resistance training.

A review of isometric strength training found that it can improve maximal strength, rate of force development and certain dynamic performance measures. The adaptations are influenced by contraction intensity, contraction duration, training intent and joint angle. Isometric strength gains also tend to be partly specific to the joint positions used during training. (⁠PubMed)

Most of the research included in this review was not conducted exclusively in prepubertal children. Therefore, adult isometric programming recommendations should not be copied directly into youth training programs.

For children, the priority should be positional competency, controlled force production and intent—not maximal loading.

One of the most persistent myths in youth development is that strength training is ineffective before puberty because children have lower concentrations of anabolic hormones.

Children can become considerably stronger before puberty.

The mechanisms may differ from those seen in mature adults. Early strength improvements in prepubertal athletes appear to be influenced heavily by neurological factors, including improved motor-unit recruitment, muscle activation, intermuscular coordination and familiarity with the task.

Ozmun and colleagues reported significant strength improvements in prepubertal children following resistance training without corresponding increases in arm circumference or skinfold measurements. The researchers also found increased muscle activation, supporting the role of neural adaptation in early strength development. (⁠PubMed)

Ramsay and colleagues also demonstrated that prepubescent boys could improve strength through supervised resistance training. (⁠PubMed)

This does not mean hypertrophy is impossible before puberty. It means that improvements in coordination and neural recruitment may make a particularly important contribution to early strength gains.

Isometric exercises can fit within this developmental process because they allow children to practice producing force in stable and understandable positions.

There are very few studies examining whether isolated isometric training changes sprint biomechanics in truly prepubertal children. Most studies either measure isometric strength as an assessment or combine isometric exercise with jumping, sprinting or dynamic resistance training.

A study by Latorre Román and colleagues examined a 10-week contrast-training program in prepubertal basketball players with an average age of approximately 8.7 years. The program was performed twice per week and combined one isometric exercise with two plyometric exercises.

The experimental group improved sprint and change-of-direction performance compared with the control group. (⁠PubMed)

This study supports the use of combined neuromuscular training in children. It does not prove that the isometric exercise caused the sprint improvements. Because isometrics and plyometrics were performed together, the independent contribution of each training component cannot be determined.

The correct interpretation is that isometrics may be useful as one part of an integrated program—not that static holds alone are sufficient to develop sprint speed.

The isometric mid-thigh pull is commonly used to evaluate maximal force and force-time characteristics.

Research involving elite youth male soccer players has shown that absolute isometric force generally increases with age and maturation. Larger and more mature athletes will usually produce greater absolute force than smaller, less mature athletes. (⁠PubMed)

That creates a problem when comparing children.

An athlete may improve absolute force simply because body mass and muscle size have increased. Relative force, impulse and early force-time measures may provide additional context, but each metric has limitations.

An isometric assessment can help describe an athlete’s force capacity. It cannot independently diagnose sprint mechanics.

A strong isometric test does not establish that an athlete can orient force effectively, coordinate high-speed limb movement or maintain efficient mechanics during acceleration.

Testing should support coaching decisions, not replace observation of the sprint itself.

Loaded running usually refers to sprinting against external resistance. Common methods include:

• Sled towing.

• Partner resistance.

• Resistance bands.

• Uphill running.

• Weighted vests.

• Motorized resistance devices.

The purpose of resisted sprinting is generally to increase the force demands of acceleration while preserving enough sprint-specific movement to produce transfer to unresisted running.

The central programming question is not simply how much resistance an athlete can move.

The more important question is whether the resistance allows the athlete to maintain a recognizable sprint action.

When resistance becomes excessive, the task may no longer resemble sprinting. The athlete may demonstrate prolonged ground contacts, excessive trunk lean, reduced limb recovery, limited hip projection or a walking-like pushing strategy.

At that point, the exercise may still develop general force, but it should not automatically be described as sprint-mechanics training.

Resisted Sprinting Before Peak Height Velocity

The evidence for resisted sprint training in younger athletes is mixed.

Rumpf and colleagues examined 32 young athletes divided into pre-PHV and mid-/post-PHV groups. The athletes completed six weeks of resisted sled towing using loads of approximately 2.5–10% of body mass.

The pre-PHV group did not demonstrate significant improvements in sprint performance. The mid-/post-PHV group showed improvements in sprint time, velocity, power and horizontal-force measures. (⁠PubMed)

These findings suggest that maturation may influence how athletes respond to resisted sprinting. More mature athletes may possess greater strength and neuromuscular capacity to benefit from the additional resistance.

A separate study by Morris and colleagues involved 73 elite male academy soccer players aged 12–18. Participants completed six weeks of sled towing twice per week, progressing from 10% to 30% of body mass.

The intervention produced minimal changes in sprinting, jumping and isometric strength across pre-, circa- and post-PHV groups. The authors concluded that the intervention primarily maintained physical qualities during the competitive season. (⁠SciOpen)

These studies do not demonstrate that resisted sprinting is ineffective. They show that resisted sprinting is not a guaranteed solution and that adaptation depends on maturity, training history, loading, program length, training phase and the characteristics of the athlete.

The principle of specificity matters.

To improve unresisted sprinting, athletes need regular exposure to unresisted sprinting. Resisted runs can support acceleration development, but they cannot fully reproduce the velocity, timing, elastic demands and coordination of unrestricted sprinting.

This is particularly important before puberty.

Young athletes are still learning how to control their bodies at speed. Too much resisted running may reduce opportunities to develop natural sprint rhythm and high-velocity coordination.

A more appropriate model is to use low-volume resisted accelerations as a supplemental exercise while keeping unresisted sprinting as the primary speed stimulus.

The load should be selected according to the desired outcome and the athlete’s mechanics, rather than using a fixed percentage for every child.

Research provides stronger support for programs that combine strength, jumping and sprinting than for programs built around one isolated method.

Rodríguez-Rosell and colleagues studied pre-PHV soccer players who completed six weeks of low-load, high-velocity resistance training combined with plyometrics and sprinting.

The strength-training group improved 10- and 20-meter sprint performance, countermovement-jump performance and strength measures, while the control group showed no significant improvements. (⁠PubMed)

This study does not establish that every exercise used in the program was equally effective. It supports a broader principle: young athletes respond well to developmentally appropriate programs that expose them to multiple related neuromuscular qualities.

An umbrella review of resistance training in youth also found strong evidence that resistance training improves physical fitness, with the largest effects generally occurring in outcomes most similar to the training performed. The authors emphasized the importance of training specificity and the need for more research involving prepubertal children and female athletes. (⁠PubMed)

The following model is a practical interpretation of the current evidence rather than a rigid scientific protocol.

1. Teach Movement Competency

Young athletes should first learn how to control basic positions and movement patterns.

This includes:

• Standing and split-stance posture.

• Hip projection.

• Trunk and pelvic control.

• Landing and deceleration.

• Marching, skipping and low-level running coordination.

• Single-leg balance and force acceptance.

These skills create the physical vocabulary required for more advanced sprint and strength training.

2. Develop General and Relative Strength

Strength training should be supervised, technically appropriate and progressively loaded.

Useful options may include:

• Split squats.

• Step-ups.

• Hip hinges.

• Push-ups and rows.

• Loaded carries.

• Calf-strength exercises.

• Landing and jumping progressions.

• Medicine-ball throws.

International position statements support properly supervised youth resistance training when exercise selection, technique and progression are appropriate for the athlete’s developmental level. (⁠PubMed)

3. Use Isometrics to Teach Force and Position

Isometrics can provide a bridge between movement instruction and dynamic force production.

Examples include:

• Split-squat isometric holds.

• Calf isometric holds.

• Wall-drive positions.

• Bridge variations.

• Side-plank variations.

• Overcoming isometric pushes against an immovable object.

The emphasis should be on posture, tension, breathing, intent and control. Extremely long holds and maximal external loads are rarely necessary for beginners.

4. Sprint Frequently at Low Volume

Sprinting itself remains the most specific speed-development exercise.

Young athletes generally benefit from short, high-quality sprints with complete recovery. Fatigue should not become so great that posture, rhythm and intent deteriorate.

Acceleration distances of approximately 5–20 meters can provide opportunities to practice projection and early acceleration without producing excessive fatigue.

5. Introduce Resistance Conservatively

Resisted sprinting may be introduced when the athlete can demonstrate consistent unresisted acceleration mechanics.

The resistance should not cause the athlete to lose coordination or turn the sprint into a slow pushing task.

The goal is not to move the heaviest possible sled. The goal is to create an overload that supports the intended sprint quality.

6. Pair Capacity With Expression

Strength and isometric exercises build force capacity. Jumps and medicine-ball throws teach rapid force expression. Sprinting teaches the athlete to apply force within the specific timing and coordination demands of running.

A complete youth program should connect all three.

The research does not support treating children as miniature professional athletes.

Coaches should avoid:

• Using chronological age as the only measure of readiness.

• Assuming heavy resistance automatically improves acceleration.

• Replacing sprinting with sled work.

• Treating isometric test scores as sprint-technique evaluations.

• Using fatigue-based sprint sessions that reduce movement quality.

• Applying adult loading recommendations without modification.

• Claiming that one exercise directly prevents injuries or guarantees speed development.

Children need progressive exposure, not premature specialization in advanced loading methods.

Prepubertal athletes are capable of developing strength, speed and power.

Their training should not be restricted to light activity out of fear that resistance exercise will interfere with growth. Scientific position statements and intervention studies support supervised, developmentally appropriate resistance training for children. (⁠PubMed)

At the same time, more resistance is not automatically better.

Isometric exercises can improve force control, positional strength and neuromuscular recruitment. Resisted sprints can overload acceleration. Neither method replaces the need to sprint, jump, coordinate and move freely.

The most defensible approach is an integrated developmental system:

Teach the athlete to control position, develop relative strength, produce force rapidly and repeatedly practice high-quality sprinting.

The objective before puberty should not be to create adult training numbers. It should be to build the movement, strength and coordination foundation that allows future speed and power to emerge.

Train With a Ground Force System

At Ground Force Strength and Conditioning Training Systems, youth speed development begins with movement analysis rather than generic drills.

We evaluate how athletes control movement, produce force and express that force during sprinting and sport-specific tasks. Training is then progressed according to the athlete’s developmental level, physical profile and individual needs.

The result is a structured approach designed to develop stronger, faster and more adaptable athletes without forcing adult training methods onto developing bodies.

Scientific References

Faigenbaum, A. D., Kraemer, W. J., Blimkie, C. J. R., et al. (2009). Youth resistance training: Updated position statement paper from the National Strength and Conditioning Association. Journal of Strength and Conditioning Research, 23(Suppl. 5), S60–S79. doi:10.1519/JSC.0b013e31819df407.

Latorre Román, P. Á., Villar Macias, F. J., & García Pinillos, F. (2018). Effects of a contrast training programme on jumping, sprinting and agility performance of prepubertal basketball players. Journal of Sports Sciences, 36(7), 802–808. doi:10.1080/02640414.2017.1340662.

Lesinski, M., Herz, M., Schmelcher, A., & Granacher, U. (2020). Effects of resistance training on physical fitness in healthy children and adolescents: An umbrella review. Sports Medicine, 50, 1901–1928.

Lloyd, R. S., Faigenbaum, A. D., Stone, M. H., et al. (2014). Position statement on youth resistance training: The 2014 International Consensus. British Journal of Sports Medicine, 48(7), 498–505.

Lum, D., & Barbosa, T. M. (2019). Brief review: Effects of isometric strength training on strength and dynamic performance. International Journal of Sports Medicine, 40(6), 363–375. doi:10.1055/a-0863-4539.

Morris, R. O., Jones, B., Myers, T., et al. (2020). Isometric mid-thigh pull characteristics in elite youth male soccer players: Comparisons by age and maturity offset. Journal of Strength and Conditioning Research, 34(10), 2947–2955.

Morris, R., Myers, T., Emmonds, S., Singleton, D., & Till, K. (2021). Does resisted sled towing improve the physical qualities of elite youth soccer players of differing maturity status? Journal of Science in Sport and Exercise, 3(1), 75–87. doi:10.1007/s42978-020-00087-w.

Ozmun, J. C., Mikesky, A. E., & Surburg, P. R. (1994). Neuromuscular adaptations following prepubescent strength training. Medicine and Science in Sports and Exercise, 26(4), 510–514.

Ramsay, J. A., Blimkie, C. J. R., Smith, K., Garner, S., MacDougall, J. D., & Sale, D. G. (1990). Strength training effects in prepubescent boys. Medicine and Science in Sports and Exercise, 22(5), 605–614.

Rodríguez-Rosell, D., Franco-Márquez, F., Pareja-Blanco, F., et al. (2016). Effects of six weeks resistance training combined with plyometric and speed exercises on physical performance of pre-peak-height-velocity soccer players. International Journal of Sports Physiology and Performance, 11(2), 240–246. doi:10.1123/ijspp.2015-0176.

Rumpf, M. C., Cronin, J. B., Mohamad, I. N., Oliver, J. L., & Hughes, M. G. (2015). The effect of resisted sprint training on maximum sprint kinetics and kinematics in youth. European Journal of Sport Science, 15(5), 374–381.

Wdowski, M. M., Noon, M., Mundy, P. D., Gittoes, M. J. R., & Duncan, M. J. (2020). The kinematic and kinetic development of sprinting and countermovement-jump performance in boys. Frontiers in Bioengineering and Biotechnology, 8, 547075. doi:10.3389/fbioe.2020.547075.

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