Squat & Vertical Jump: what’s the link?

In many sports, vertical jumping is a valuable athletic quality to have in your arsenal if you want to perform at your best. To develop it, weight training is often recommended, with the loaded Back Squat at the forefront. Although at first glance, the use of this exercise to help jump higher seems obvious, a closer examination leads us to question the real link between squat strength and vertical jumps. This article seeks to shed light on some of the answers.

Scientific Basis

Concentric contraction: contraction during which the length of the muscle decreases (i.e. the muscle « shortens »).

Isometric contraction: contraction during which the length of the muscle doesn’t change.

Eccentric contraction: contraction during which muscle length increases (i.e. the muscle « lengthens » or « stretches »).

Plyometric action: rapid transition from eccentric to concentric contraction, with an isometric-like action in between.

Eccentric, isometric and concentric actions

Dynamic movements involve the stretch-shortening cycle (SSC), a mechanism that takes place during a rapid transition from eccentric to concentric contraction (as in a jump, for instance) and which involves both muscles and tendons. This mechanism comprises several aspects, including :

– The stretch reflex, which increases muscle activation (through the number and size of fibers recruited) when a muscle is rapidly stretched (in order to prevent the muscle from tearing),

– Elastic action of tendons (and other tissues): muscles activate to resist lengthening so that tendons can stretch and store energy at the end of the eccentric phase (in a very brief phase resembling isometrics), which they can then release during the concentric phase.

An optimized SSC leads to better energy conservation in dynamic efforts, as well as improved propulsive forces (concentric phases).

But that’s not all: during dynamic movement, muscles spindles (MS), proprioceptive sensors in muscles, detect the extent and speed of change in muscle length (i.e. muscle stretch), which determines whether or not the stretch reflex is triggered and the subsequent increase in force production.

Alongside these, the golgi tendon organs (GTOs), proprioceptive sensors in tendons, are responsible for detecting the amount of tension present in the musculotendinous unit. If the tension is too great for the nervous system and hence constitutes a danger to the body, they will inhibit force production, counteracting the action of the MS.

Dynamic correspondence between squatting & jumping

The dynamic correspondence between 2 movements reflects their similarity level in terms of muscle position, function, metabolic demands, time characteristics of force production, and many other factors.

Jumping

Our model is the Countermovement Jump (CMJ). The various phases of this jump will be discussed in greater detail in a future article; for now, a simplified description suffices as a basis to express the ideas presented throughout this article.

CMJ

In a CMJ, during the lowering phase, we first have a passive stretch in the quads and glute muscles; we produce less force than what is needed to stay upright, partially deactivating certain muscles to build momentum by letting gravity pull us along. The  »amount’’ of momentum and its speed influence the extent of eccentric stretching.

Then, towards the end of the lowering phase, muscles start to rapidly (re)generate force; then, at the bottom of the movement, co-contractions are produced throughout the body – all the muscles around the joints will activate simultaneously to stabilize these joints and resist the body’s ‘’fall » (avoiding further stretching of muscles).

For example, during a jump, the quadriceps and hamstrings contract at the same time to stabilize the knee and avoid a greater stretch of the quad muscles.

After this phase, which looks like isometrics – but isn’t really, because although the muscles resist lengthening at the end of the lowering, the tendons are stretched – comes the concentric or propulsion phase. For it to be optimal, some muscles activated during co-contraction must relax rapidly to allow others to contract to their fullest.

In the same example, the hamstrings must then relax quickly to avoid slowing down and hindering the contraction of the quadriceps.

Slower lowering limits the use of the SSC, so overall force production is lower, and we can’t jump as high as we could have. However, if the body is not accustomed to a fast and powerful eccentric, it will be unable to use the SSC in the best possible way: the GTOs will come into play, antagonist muscles are going to ‘’brake » to the propulsion, and the tendons won’t act optimally.

Over time, better athletic performance is not necessarily due to greater force-generating capacity or faster muscle activation, but may simply result from GTOs inhibition and faster relaxation of specific muscles after their activation.

Generally speaking, the faster the reversal of movement, the more energy is returned from the tendons; the slower the reversal, the less energy is returned from the tendons, and the more the muscles are called upon.

Squatting & differences with jumping

When performing a squat movement with a loaded barbell on the back (Back Squat), the contraction dynamics are different:

• During the lowering, there is no relaxation, force production is constant (even if its magnitude varies) and co-contractions are present throughout the all movement,
• The transition between the eccentric and concentric phases is too slow to induce an optimal SSC,
• On the concentric phase, the movement slows down at the end for stability and safety matters (it’s better to be cautious when a there’s load on the spine).

The differences between a CMJ and a Back Squat are therefore manifold:

1. The CMJ involves a relaxation and use of the SSC not found in the Back Squat; there’s no use of the stretch reflex in the second case, which can help increase muscle activation and therefore overall force production,

2. The glutes function in opposite ways between both movements (see podcast n°1 in reference 104): in a squat, the peak force production of the glutes is in a position with the hips flexed and the knees at 90°, whereas in a CMJ this peak is when the feet leave the ground during the propulsion phase,

3. When performing a Back Squat, there’s a deceleration at the end of the movement so that the feet don’t leave the ground and the bar stays firmly on the back, whereas for a CMJ the acceleration is constant and maximum throughout the ascent,

4. Peak forces are lower for a loaded Back Squat than for a CMJ, while contraction times are longer (references 77, 78, 79 and 84),

5. The training of each movement leads to distinct muscular and tendon adaptations (nonetheless potentially complementary from a preventive standpoint), with the action of the musculotendinous unit being quite specific to the effort.

The poor correlation between strength performance in bodybuilding and athletic performance such as jumping, changing direction and sprinting has been observed in various studies (Zabaloy & al. 2020; Falch & al. 2020).

The scientific literature (Rhea & al., 2016) also indicates that strength gains are specific to the speed and types of contraction, the joint angles trained and the intent of movement. A Back Squat performed with a very heavy load is therefore too slow to hopefully get a direct strength transfer to athletic efforts (sprinting, changes of direction, jumps, etc., performed in 0.25s or less).

In addition, when performed in a full range of motion (i.e. going as low as possible on the way down), the critical joint angles for dynamic efforts (involving high force production in a relatively small ranges) are not optimally trained:

– The full range of motion limits the maximum load used, and therefore limits the training load in the interesting range because it’s harder to reverse the movement when we’re deeper in a squat,

– The bigger the range of motion, the greater the fatigue over the interesting range compared to executing the movement only over the interesting range,

– There are no stops – and therefore no eccentric or isometric force production – in the positions specific to dynamic sports movements.

Therefore, in order to maximize the transfer of strength work to sport, squats should be performed in partial range of motion with some speed constraint. This enables the essential joint angles to be better loaded, and higher peak forces – particularly in the eccentric phase – to be achieved (as a greater load can be used).

Full ROM vs Partial ROM

However, full range training is not to be thrown away altogether. There are still some benefits:

• Strength gains for beginners or those with little training,
• Increased recruitment of motor units in muscles (especially fast-twitch fibers),
• Potentially better hypertrophy than with partial range,
• Improved mobility and health of passive tissues (cartilage, ligaments & bones).

Nevertheless, beyond not particularly leading to performance gains, a substantial volume of squat in full range can also have negative effects:

• Modification of the tension-length relationship (see my recent article on stretching), shifting it towards deeper, less performance-related joint angles,
• Possibility of aggravating symptoms on a painful tendon (e.g. in the case of patellar tendinopathy or Jumper’s Knee).

Thus, at some point, it becomes crucial to find the right balance between partial- and full-range squat work if you want to maximize athletic performance – including vertical jumping. The principles of joint angles, speed of movement, intention and task-specific coordination will become increasingly important.

In the meantime, too much strengthening at all – regardless of range – without sufficient dynamic effort also has its drawbacks:

• Significant increase in tendon stiffness, which can be both beneficial to performance and dangerous for muscle injury,
• Increased co-contractions (i.e. activation of the brakes during the concentric phase) and less efficient use of the SSC,
• Exaggerated hypertrophy, which can slow down muscle contraction speeds.

To conclude on this subject, it’s essential to point out that squat strength gains over time may simply result from an improved skill at the squat movement performed with load, without any impact on athletic ability.

Variations of Vertical Jumping

A first issue arises when we look at the standing vertical jump: it’s possible to use 2 different strategies to perform well. Jump height is a function of total impulse, which depends on the force produced and the duration over which it is produced.

This height can therefore be increased either by producing more force over the same duration, or by increasing the duration during which force is produced (i.e. by dropping lower during the lowering phase) – the second method being somewhat easier than the first. The full range Back Squat is of greater interest when this second method is considered.

Demonstration of 2 different CMJ strategies

Strategy 1 = long lowering / Strategy 2 = fast lowering

However, in the vast majority of sporting activities, we don’t get the luxury of having all the time in the world. For instance, with rebounding in basketball, you need to be able to jump high AND fast, which implies a fairly small range. To improve performance, we must therefore strive to improve impulse by increasing the amount of force produced and/or by decreasing its duration.

It should also be noted that trying to jump high (without a run-up) by only increasing the duration of force application can also modify the tension-length relationship of the quads and glutes, thus potentially impacting performance on run-up jumps, changes of direction and sprints.

A second issue emerges when we realize that most jumping actions in sporting situations are performed with a prior (and variable) run-up. This run-up implies a time constraint: there is very little time to generate force on the ground and maximize the SSC. Improving jumping height with an approach can only be achieved by increasing force production capacity.

Moreover, jumping after a run-up is a neurologically very complex task, and very different from jumping without a run-up in terms of posture, inter-muscular coordination, intramuscular timing, motor unit synchronization, muscular and tendon actions…

There are also discrepancies in posture between jumping with an approach (whether with 1 or 2 feet), jumping without it and squatting with a bar on the back: the latter requires more hip flexion, a more tilted torso, potentially different foot position and toe orientation, with perhaps more demands on the glutes; whereas the former involves less hip flexion, a more upright torso, less knee flexion, and is more demanding on the quads.

Different postures for different movements

From left to right: 1-foot approach jump / 2-foot approach jump / Back Squat

As a reminder, strength gains are, among other things, specific to the postures and joint angles trained. Some machines, such as the Hack Squat or the Leg Press in supine position, could enable to train with a more similar posture to the one in which you produce force during an approach jump – another discussion for another day.

If you want to maximize your athletic performance, the goal should be to improve your ability to jump with an approach (and varying it), not just to improve your ability to jump on the spot (and even less to improve your ability to squat heavy loads). Thus the focus should be on finding exercises that increase force production capacity under similar conditions in terms of movement speed, joint angles, intent, and musculotendinous actions.

Practicing the task that you want to be better at is also crucial, as anything done in the weight room is too far removed from the task itself neurologically speaking.

How to jump higher?

In my opinion, strength work in a squat pattern remains fundamental: despite its limitations, it still brings some physiological gains, and il increases the general force production capacity of certain key muscles. Being « strong enough » is a basis from which more specific qualities can be built on. We’re not seeking for a direct transfer with it, we’re just looking to increase strength potential.

Once a certain strength level has been reached in the squat pattern – and it becomes increasingly difficult to increase the loads – the focus should simply become to maintain this level. We’re lucky, because according to Androulakis-Korakakis & al. (2019), max strength is easily maintained. We can then spend more time using other methods, more transferable to athletic efforts.

A first interesting tool for improving athletic performance (and one that can be found in the weight room) is « fast strength » work, to get more specific adaptations. High-speed strength exercises have many benefits:

• Optimization of co-contractions – and reduction of « brakes » in the concentric phase,
• Improvement in fiber activation speed and contraction frequency,
• Improved elastic storage capacity of collagen structures (tendons, fascia…) (Fascial Fitness, Divo G. Müller & Robert Schleip),
• Potential improvement in active stiffness (i.e. the ability to resist stretching, which corresponds to the ability to rapidly produce force during an eccentric contraction).

Among other things, olympic weightlifting and its derivatives make it possible to target different aspects of an athletic effort such as jumping; this will be the subject of a future article.

A second tool, which can be found both in the weight room and on the field, is plyometrics. This method allows to work on muscle and joint sequencing, muscle-tendon interaction, SSC, muscle activation timings (for co-contractions in particular) and can even be used to desensitize OTGs.

Finally, if the goal is to jump higher from a run-up, it’s key to train this task directly. This is the only way to express the potential built up by all other methods mentioned above. Regularly jumping from an approach helps to :

– Improve movement technique (by training to transform horizontal momentum into vertical movement) and make it more « fluid » and natural (the body gets used to the task with practice),

– Teach the brain and nervous system to coordinate all muscles during the movement (intra- and inter-muscular synergies), by controlling activation and relaxation timings precisely to obtain optimal co-contractions (in terms of timing and duration),

– Optimize the SSC, as well as the use of the MS and the inhibition of the GTOs (by progressively increasing the speed and distance of the run-up in order to increase the impulse).

In contrast to maximum strength capacity, elasticity and competency of movement on complex tasks are qualities that are not easily retained. It’s therefore vital to practice them frequently if you want to perform them to the best of your ability.

REFERENCES

1. ‘’The Stretch-Shortening Cycle: Proposed Mechanisms and Methods for Enhancement’’, Turner & Jeffreys, 2010
2. ‘’Joint-Angle Specific Strength Adaptations Influence Improvements in Power in Highly Trained Athletes’’, Rhea & al., 2016
3. ‘’Potentiation of concentric force and acceleration only occurs early during the stretch-shortening cycle’’, McCarthy & al., 2012
4. ‘’Development of maximal speed sprinting performance with changes in vertical, leg and joint stiffness’’, Nagahara & al., 2016
5. ‘’Influence of Sex and Maximum Strength on Reactive Strength Index-Modified’’, Beckham & al., 2019
6. ‘’Effects of squat training with different depths on lower limb muscle volumes’’, Kubo & al., 2019
7. ‘’Changes in Dynamic Strength Index in Response to Strength Training’’, Comfort & al., 2018
8. ‘’Human capacity for explosive force production: neural and contractile determinants’’, Folland & al., 2014
9. ‘’Effect of knee position on hip and knee torques during the barbell squat’’, Fry & al., 2003
10. ‘’Neuromuscular adaptations to 4 weeks of intensive drop jump training in well-trained athletes’’, Alkjaer & al., 2013
11. ‘’The Minimum Effective Training Dose Required to Increase 1RM Strength in Resistance-Trained Men: A Systematic Review and Meta-Analysis’’, Androulakis-Korakakis & al., 2019
12. ‘’Squatting Kinematics and Kinetics and Their Application to Exercise Performance’’, Schoenfeld, 2010
13. ‘’Barbell Squat Relative Strength as an Identifier for Lower Extremity Injury in Collegiate Athletes’’, Case & al., 2020
14. ‘’Association of strength and plyometric exercises with change of direction performances’’, Falch & al., 2020
15. ‘’Unilateral vs. Bilateral Squat Training for Strength, Sprints, and Agility in Academy Rugby Players’’, Speirs & al., 2016
16. ‘’Strength training : structure , principles , and methodology’’, D. Schmidtbleicher, 2006
17. ‘’Stretch-Shortening Cycle (SSC)’’, site Web Science for Sport (2023)
18. ‘’Concentric, isometric & eccentric training – Differences, benefits & examples by Elizabeth Criner’’, site Web Athletic Lab
19. Fascial Fitness, Müller & Schleip, Elsevier Science 2011
20. Dan Fichter Patreon Subscriptin
21. Instagram account @PJFPerformance
22. Contract-relax methods, website EdgeU
23. Training residuals, website EdgeU
24. 5 questions to think about, website EdgeU
25. Skill or strength? Training a new movement, website EdgeU
26. Neuromuscular System and why we care, website EdgeU
27. Strain vs Exposure, website EdgeU
28. Special Work Capacity (Specific) – Some Thoughts Inspired By Dr. Bondarchuk, website EdgeU
29. Top 5 Instagram Posts of November, website EdgeU
30. December Top 5 Instagram Posts, website EdgeU
31. Social Media Review EdgeU, website EdgeU
32. Know your athlete, website EdgeU
33. Supported versus Assisted, website EdgeU
34. Know Your Goals, website EdgeU
35. Sport Specificity Spectrum, website EdgeU
36. Neural Adaptations Basics, website EdgeU
37. Movement is learning, website EdgeU
38. Understanding The Importance of Velocity, website EdgeU
39. Force Vectors gravity, website EdgeU
40. General Training Principles, website EdgeU
41. Motor potential and periodization, website EdgeU
42. Force velocity curve breakdown of application, website EdgeU
43. Optimizing performance: understand impulse, website EdgeU
44. Motor Learning Interference, website EdgeU
45. Programming impulse example, website eb EdgeU
46. Isometrics critical joint angles, website EdgeU
47. Strength Relations, website EdgeU
48. Coach’s Eye countermovement jump, website EdgeU
49. Impulsive loading, website EdgeU
50. Neuro Conditioning, website EdgeU
51. Ballistic contraction, website EdgeU
52. Contraction-relaxation origin and what it means, website EdgeU
53. Neuromuscular adaptations: basics, website EdgeU
54. RFD Breakdown, website EdgeU
55. Understanding Relationships, website EdgeU
56. How movement happens: mecanical and electrical delay, website EdgeU
57. Shock Method: review, website EdgeU
58. Impulse: what we need to know, website EdgeU
59. Feedforward explanation, website EdgeU
60. Skill in sport, website EdgeU
61. Programming different ROM, website EdgeU
62. Force-plates & squat: how you move matters, website EdgeU
63. Performance limited by skill or physiology ?, website EdgeU
64. Articular angle specificity, website EdgeU
65. Hatfield squat better than back squat? , website EdgeU
66. Rhythm Squat Breakdown, website EdgeU
67. Training a goal, not an exercise, website EdgeU
68. Assessing SSC, website EdgeU
69. Hyperthrive Athletics: training for rotational power & throwing athletes, website EdgeU
70. Eccentric lowering velocity, website EdgeU
71. Specificity: quick breakdown, website EdgeU
72. Co-contractions, stability & strength, website EdgeU
73. Stretch Shortening Cycle (part one), website EdgeU
74. Research discoveries, website EdgeU
75. Science of Squat Depth, website eb EdgeU
76. Jump training: should we practive parts of the movement?, website EdgeU
77. The truth about squat for VJ, website EdgeU
78. The truth about quarter squat vs full squat to jump higher, website EdgeU
79. Articular angle specificity, website EdgeU
80. Squat Depth, website EdgeU
81. ROM & Squat: controlling the stress, website EdgeU
82. Advanced Training Method: Hatfield Squats, website EdgeU
83. Advanced Training Method: Trap Bar DL, website EdgeU
84. Best Squat Variation to jump higher, website EdgeU
85. Pin Squat & Oscillatory Reps Breakdown, website EdgeU
86. 5 tips for max intent, website EdgeU
87. Drop Catch Breakdown, website EdgeU
88. Sometimes lifting isn’t important, website EdgeU
89. Narrow Stance Heel Elevated Squat Discussion, website EdgeU
90. Coaching Tool: Pulse ISO, website EdgeU
91. Review on Science and Practice of Strength Training (chapters 1-11), website EdgeU
92. Cours –  Developing muscular power, website EdgeU
93. Cours –  Strength qualities, website EdgeU
94. Cours –  Speed-strength training, website EdgeU
95. Cours –  RFD, website EdgeU
96. Cours –  Elasticity, website EdgeU
97. Crazy Explosive Series- Episode 2: Force Absorption (BEST tips for vertical jump/explosive gains), PJF Performance YouTube Channel
98. Crazy Explosive Series- Episode 3: Force Production, PJF Performance YouTube Channel
99. Crazy Explosive Series- Episode 4: Elasticity (Best Tips for Improving Vertical Jump/Speed), PJF Performance YouTube Channel
100. Top 3 Vertical Jump Exercise-Trap Bar Deadlift, PJF Performance YouTube Channel
101. 3 Vertical Jump Exercises w/ Pro Dunker Chris Staples, PJF Performance YouTube Channel
102. The Truth About Squats for Vertical Jump, PJF Performance YouTube Channel
103. Best Exercises for Training Deep Knee Bend/Full Range of Motion, PJF Performance YouTube Channel
104. PJF Podcast – episodes 1, 2, 6, 7, 8, 9, 10, 12, 14, 16, 17, 19, 20, 27, 40, 41, 44 & 51
105. Combo’s Court Podcast 82 – Paul Fabritz, NBA Performance Specialist
106. StrongByScience Podcast 2 – Cory Schlesinger, Stanford
107. Mind Pump: Raw Fitness Truth Podcast 900 – NBA Superstar Sports Performance Coach Paul Fabritz
108. Mind Pump: Raw Fitness Truth Podcast 1017 – Max Schmarzo- Strong by Science