M Newman: Strength Qualities of the 100m Sprinter

Strength Qualities of the 100m Sprinter

M Newman

To understand what is required to be successful over the 100m sprint, the event must be divided into three phases. The structure of the velocity-time curve is the same for every sprinter, over the distance. The three phases are the start-acceleration, maximal speed, and speed maintenance. Each phase is defined by physiological and biomechanical characteristics.

Velocity Curve of Elite and Beginner Athlete


Figure 1 the velocity curve of the 100m sprint showing the performance curve

Of an elite and beginning athlete with the phases of the elite sprinter identified.

The phases require slightly differing qualities of strength and technique. The purpose of this article is to concentrate on the strength requirements of the 100m sprint. Each phase will be discussed purely in terms of the dominant strength required.

100m Strength Qualities

Figure 2. The different phases of the 100m sprint and the body

positions that dictate ground contact and the different strength

qualities of the 100m sprint.

The start

Block clearance

The start of the 100m sprint consists of the block clearance and the first two strides proceeding. New research by Dr R Mann and the USATF has shown that elite sprinters whether male or female attain over 50-60% of their maximal velocity after the first two strides of the 100m sprint.

The block clearance requires a form of strength known as explosive isometric strength. This type of strength is expressed when a significant amount of resistance has to be overcome, example overcoming the bodyweight of a sprinter in the blocks. The duration of the front block push-off is approximately 200-300ms and the back foot is 150-180ms. This length of time allows the sprinter to generate explosive strength. There is no pre-stretch of the muscles before the push from the blocks, the start is initiated from a static position with no movement. The feet have very little rebound; instead they push and move away from the body on ground contact. At this point it must be emphasised that other forms of strength are required during this phase and other parts of the sprint; but the dominant expression of strength can be characterised as explosive strength.

Initial first strides

During the second stride, the explosive and maximal strength of muscle contractions, (rather than tendon action) is the performance limiting factor. Explosive isometric strength transitions into explosive ballistic strength. This type of strength can be generated in approximately 120-200ms (average contact times of the first two strides). The ground contact times of the first two strides are in the region of 120-200ms. Explosive ballistic strength is expressed when relatively small resistance (as the body overcomes inertia there is less resistance experienced during the acceleration phase). There is a definite stretch-shortening cycle during this phase dominated by muscular contractions. During the first two to seven strides, a stretch-shortening of muscle has a major part to play, but this stretch-shortening cycle (SSC) is much slower than the fast stretch-shortening cycle experienced at top speed in the 100m event. The prime movers (muscles responsible for most of the work done) are the gluteus maximus, quadriceps, calf and shin muscles.

Both types of explosive strength involving a slow SSC, can be developed using exercises that require a large amount of knee flexing, such as squat jumps, the squat, and sledge pulls to 10-30m, alternative bounds with full strength effort and jumps upward onto boxes. The pulling of an excessively heavy sledge will affect sprint technique. A heavy sledge may develop explosive isometric strength but not explosive ballistic strength, which is needed for the two to seven strides after block clearance.

The acceleration phase

The acceleration or transition phase commences after the first two strides of the 100m sprint. This phase starts around 10m and ends at the 50m mark. Ground contact times fall in a range of 70-110ms. Such low ground contact times are too short for the athlete to apply maximal or near maximal explosive strength. The faster stretch-shortening cycle during this phase is known as explosive reactive reflex strength or elastic strength.

The stretch-shortening cycle during this phase is so fast that the kind of speeds needed for applying force requires the activation of elastic tissue within muscles, and the greater use of tendons such as the achilles and the ilio-tibial band. Undoubtedly this type of strength is the defining quality of the fastest 100m sprinters.

The maximal speed phase

The maximal speed phase of the 100m sprint is reached typically between the 50-70m zone. Maximal speed is considered to be attained when 95% of the highest speed is attained. The phase can last until the 90m mark. Explosive reactive reflex strength, ballistic strength and isometric strength are the limiting factors during the maximum speed section.

The hip flexors, (the muscles responsible for the knee drive) require explosive ballistic strength. The muscles responsible for the knee drive generate a very large amount of strength and power. This type of strength is needed to initially accelerate the knee and the thigh when the foot leaves the ground to a position where the knee is furthest away from the body. Knee drive drills and exercises to develop the rectus femoris, iliacus and psoas muscle must be done. The psoas muscle is the most difficult to train, exercises that strengthen this muscle in a specific manner are needed.

The muscles of the mid-torso warrant a special mention. This part of the 100m sprint requires isometric strength of the mid-torso muscles. During the maximal speed phase, the muscles of the mid-torso must stabilize the pelvis and maintain the upper body in an upright position. The twisting action experienced by the mid-section requires explosive isometric strength endurance. Stability of the pelvis is crucial for acquiring a favourable sprint position. The conditioning of the ilio-psoas, abdominal oblique, and erector spinae is a must for attaining high speeds. This can be developed using a variety of exercises and sets of high repetitions. Use of isometric holding exercises and dynamic repetitions are the way forward. Some elite sprinters achieve this prerequisite through high repetition abdominal work-outs with repetitions totalling 1,000 in a session.

The ability to generate strength in high stretch-shortening actions is limited by the conditioning of the hamstrings, calves and achilles tendon. Greater strength during this phase doesn’t transfer to greater speed if muscle viscosity is too high. Shorter inelastic hamstrings that are less supple are a limiting factor in this phase. Strong but supple hamstrings are necessary for attaining a higher level of maximum speed.

The lower legs of a sprinter must generate a large vertical force. These large vertical forces can only be developed by compliant (easy to stretch) tendons and stiffer muscles. Muscle stiffness in the context of the fast SSC experienced by the 100m sprinter has nothing to do with flexibility. This type of stiffness relates to the ability of the muscle to resist elongation.

The performance of the muscle-tendon complex (MTC) is crucial for attaining and maintaining high levels of maximal speed. Stiffer muscles and compliant tendons are needed. A more compliant tendon will allow muscles to be stiffer.

Using the example of a long thin and a short thick elastic band may help. A long and thing elastic band is very easy to elongate (stretch). The long thin elastic band requires less energy to stretch; and is able to recover more of the energy during the shortening phase. A shorter thicker elastic band will be much stiffer. It will require greater energy to stretch and will shorten at greater speeds but could loose more energy in the form of heat.

A long and thin tendon will be able to cycle faster between stretching and shortening and do more stretch work saving muscles such as the hamstrings from doing stretch work*. Some energy is lost when the elastic band shortens.

It is commonly held by many that muscles lengthen or work eccentrically during the initial ground contact and shorten or work concentrically during toe-off (Figure 3). Evidence from recent research has shown that muscles contract isometrically. An isometric contraction is when a muscle applies force but there is no change in length. A concentric contraction involves muscle shortening, and an eccentric contraction causes muscle to stretch.

Muscle is less efficient when stretching and shortening in comparison to tendon. Over the same distance of work, muscle is less able to reclaim energy required for stretch-shortening. Muscle generates heat and requires ATP to contract. Tendons in contrast can stretch and shorten on impact due to gravity.

A muscle is able to produce greater forces and uses predictable energy levels when it maintains constant (isometric) tension. It uses energy faster when shortening (concentric) and slower when stretching (eccentric). Muscle uses more energy when stretch-shortening than when doing the same amount of work isometrically.

As muscle power increases, the relative cost of work by concentric muscle action also increases. The benefit of using stored energy becomes a priority.

A muscle that is stiff and less compliant will work better during the ground contact time of the 100m sprint because it allows tendons to do most of the stretch-shortening work while applying force isometrically. The muscle then requires less phosphates and glycogen to do work.

Muscle can’t compete with tendon elasticity; a muscle that is stiffer will be able to maintain tension and resist stretch-shortening much faster at ground contact. The muscle will use less energy due to less work done and generate more force. The trade-off means that tendons need to be more compliant to allow muscles to be stiffer.

Muscle stiffness and tendon compliance can be trained using general weight training, plyometrics and sprint training on softer as well as harder surfaces. In particular, bounds and hops over obstacles with an emphasis on the vertical component are the most important for developing the reactive reflex strength for this phase. A heavier athlete will generally need to develop greater reactive strength than a lighter athlete. Even the 100m sprint is a weight limiting event. An emphasis on hamstring strength and power training is fundamental. Supple (less viscose) but stronger hamstrings will be able to generate the necessary strength at maximal speed.

Hamstrings and Muscle Tendon Action

Figure 3. The muscle tendon complex of the hamstrings, gluteus maximus, calves and achilles and iliotibial band.

The speed maintenance phase

The speed maintenance phase involves a mix of different strength qualities. Explosive reactive strength is still dominant, but a certain level of strength endurance comes into play. This is less so for faster sprinters because the maximal speed phase occupies a larger section of the overall sprint (refer to Figure 1). Contrary to the commonly held belief, lactic acid and lactate are not responsible for the fatigue experienced during this phase, in fact the faster and more powerful the athlete the larger the production of lactic acid and lactate. The body has the ability to convert lactic and lactate back into energy. During this phase, most of the phosphate pool would have been depleted. A larger percentage of energy will be provided by anaerobic glycolysis to maintain muscle stiffness. Blood lactate levels measured after the 100m sprint range from 7-15 mmols. Once again the greater the muscle stiffness the shorter the speed maintenance phase.

The central nervous system (CNS) which consists of the brain and the spinal column are likely to be the reason for the fatigue experienced at the end of the 100m sprint. The neural fatigue will happen regardless of the calibre of sprinter or the performance attained. Lowering of dopamine in the brain, and depletion of chemicals in the nerves are likely to decrease the rate and size of impulses travelling to the muscles.

CNS resilience can be improved through strength endurance and sprints to improve speed endurance. Adequate nutrition including amino acids can help lessen CNS fatigue over time. Runs that place a load on the CNS such as differential sprints, and ins and outs will develop the necessary CNS resilience for the 100m sprint.

Velocity Time Curve


Figure 4. The phases of the 100m sprint and the strength qualities needed.

The 100m sprint requires different types of strength in each phase (Figure 4). To be successful in the 100m, these differing types of strength must be trained optimally to increase the potential for success.

*Incidentally, if tendons attached to the hamstrings are less compliant then the potential of injury to the hamstring muscle belly increases.