Some confusion arises when endurance athletes and coaches question the need for the force produced in a maximal strength contraction. Of course, a maximal level of force is not required to complete a stride, cycle revolution, or swim stroke. So, why then is (maximal) strength considered a critical component for endurance athletes? Because training maximal strength is the only way to develop synchronous motor unit recruitment, which is the primary requirement for increasing propulsive force and resisting muscular fatigue over long-endurance performances.
For instance, in endurance running the only way to increase speed is by increasing stride length and/or stride rate, and/or decreasing foot contact time with the ground. Achieving any of these performance indices requires an increase in propulsive force. The only road to increasing propulsive force is through increasing strength. The only way to maintain an increase in propulsive force over the course of a long-endurance event is by resisting muscular fatigue, which is the same as improving muscular endurance, which is also the result of increased strength.
The three main biomotor abilities include: Force (strength), Speed, and Endurance. Because both speed and endurance derive from strength, strength (force) is considered to be the primary biomotor ability.
Strength affects all other biomotor abilities. All other biomotor abilities arise from strength and may affect each other, but don’t affect strength. For example, both speed and endurance are influenced by strength, but speed and endurance do not influence strength. For this reason, Bompa recommends that strength should be considered as the crucial biomotor ability. To improve any athletic performance, strength must always be trained in concert with the other biomotor abilities.
Most of us recognize muscular strength and power as being important to all sports that are dominated by speed and explosiveness. For instance, strength appears to significantly influence running speed. But, contemporary scientific data reveal that muscular strength is equally important in sports with large endurance components, such as long-distance running and triathlon. What might surprise you is the influence of strength on endurance, noted in the literature, demonstrating that adding resistance training to the training regimes of long-distance runners, Nordic skiers, and cyclists results in significantly greater improvements in performance compared with focusing only on endurance training.
INTERACTON OF BIOMOTOR ABILITIES AND VARIOUS ASPECTS OF SPORT PERFORMANCE
Most sports fall into one of two categories. The first, explosive POWER sports are those that require bursts of explosive movement such as starting, stopping, changing direction, sprinting and leaping. These would include: football, basketball, lacrosse, rugby, soccer, etc. The second, MUSCULAR ENDURANCE sports are cyclic in nature like running, cycling, swimming, rowing, and cross-country skiing where the primary requirement is maintaining the propulsive force of a repetitive movement pattern over long periods of time. In the sport of cycling, muscular endurance is also known as AVERAGE POWER.
To attain the performance capability of either POWER or AVERAGE POWER requires the input of strength, in the form of maximal strength. The ‘take-away’ is that it is the TRAINING PHASE known as ‘CONVERSION’ that takes maximal strength and converts it to either POWER or MUSCULAR ENDURANCE. Strength training must follow a very specific pattern, or phase sequence, if it is going to have the intended outcome of improved power or muscular endurance. The pattern is as follows:
1. General Adaptation Phase, 2. Maximal Strength Phase, 3. Conversion Phase.
If there is no maximal strength, there is nothing to convert.
Most endurance athletes and coaches seem to believe that the type of training that characterizes the conversion phase (high repetition/low resistance) is adequate, but this type of training performed alone (without the preceding General Adaptation and Maximal Strength Phases) has been shown to affect only metabolic capabilities, but NOT strength.
Muscles contract in a process known as MOTOR UNIT RECRUITMENT. Typical motor unit recruitment, even in athletes, is ‘asynchronous’, meaning that all the available motor units don’t contract simultaneously. But, motor unit recruitment can be altered through maximal strength training to become ‘synchronous’, meaning that all the available motor units contract simultaneously. The key in power sports is explosiveness which requires synchronous motor unit recruitment. Interestingly, the key in endurance sports, resistance to muscular fatigue, (also known as muscular endurance or average power) also requires the synchronous motor unit recruitment that is developed through maximal strength training.
According to Bompa, neither running uphill nor cycling uphill can provide the adaptation stimulus required to increase strength (let alone, maximal strength). Everyone who trains hills experiences some type of improvement in their performance capabilities. This uptick in performance is primarily a metabolic improvement in anaerobic glycolysis, not a change in the force producing capability of muscular contraction. Of course, cycling or running uphill requires some short-term increase in the force of muscular contraction. This is sometimes referred to as ‘residual strength’. If you think about it, your rate of force development actually goes down significantly during climbing or running uphill (think of cycling rpms or contact time with the ground in running). If you have not trained to recruit motor units synchronously and your ability to increase the rate of force development, the use of residual strength is a short-lived burst of effort that requires a significant increase in energy input (usually provided by anaerobic glycolysis). This short-term increase in effort results in the increased production and decreased clearing of lactic acid, which can reduce the actual number of motor units that can actually fire, even during asynchronous recruitment. This is definitely moving in the wrong direction for endurance racing, where resisting muscular fatigue is crucial.
Metabolism provides the energy required for muscular contraction, but is not responsible in any way for synchronous motor unit contraction, the force of muscular contraction, or the rate of force development. Training energy systems such as the oxygen system and anaerobic glycolysis is the metabolic half of the training equation. This type of training encompasses all the types of swimming, cycling, and running workouts that endurance athletes (triathletes) are familiar with. It does not however, improve the ability to create force through muscle contraction. Training the force producing capacity of muscle contraction and resistance to muscular fatigue is the other half of the equation. It is a gym-based process that can’t be achieved by swimming, cycling, or running. Without it, your training and performance can only be half-fast at best.
Motor units come in different sizes. Every muscle has motor units that increase in size from small to large. When motor unit recruitment is untrained the recruitment process is known as ‘asynchronous’ and proceeds from recruiting smaller motor units first, to larger motor units until the demand for force is met. Because the actual force required for a stride, cycle revolution, or swim stroke never approaches the requirement for maximal force production, the same group of smaller motor units is being recruited over and over, while the larger motor units never come into play. This is very inefficient, and results in muscular fatigue and the inability to maintain a given pace. When motor unit recruitment is synchronous, all (or almost all) motor units, including the larger more powerful ones are recruited together. This is far more efficient and results in resistance to fatigue and the ability to increase propulsive force.
Here’s an analogy for ‘efficiency’: Suppose there are two teams of competitors. Each team has 10 members. On each team, 5 of the members are smaller and 5 are larger and stronger. The goal for each team is to stand in a line and lift a telephone pole over their heads as many times as they can. The only rule that must be followed is that there can be no substitutions once the competition begins. The first team only sends the five smaller members out to compete, while the second team sends out all ten members… the competition begins. At first, the team using only the five smaller members can keep up with the team utilizing all ten members, but each member of the 5-man team is working much harder than each member of the 10-man team. After a short period of time, the 5-man team starts to fatigue, and finally can’t raise the telephone pole over their heads anymore. Because each member of the 10-man team has a much lighter load to lift (per man) the 10-man team is able to resist fatigue, and could actually continue lifting the given load (or producing the higher average power) indefinitely. The efficiency of the 10-man team is much greater, meaning that the effort being put forth by each member of the 10-man team (per repetition) is much less. The 10-man team represents ‘synchronous’ motor unit recruitment. The 5-man team represents ‘asynchronous’ motor unit recruitment.
Who would only send out a 5-man team? Everyone who can only recruit motor units asynchronously!
Higher efficiency results in an increase in time to exhaustion (at a given pace) and also results in less input (energy) for a given output. Efficiency is what allows you to perform at a given pace for a longer period of time. The longer the race distance, the greater the requirement for efficiency. ‘Efficiency’ is related to the biomotor ability known as ENDURANCE. Review the chart above to note that endurance derives from strength.
But, suppose you have mastered the distance? How do you get ‘faster’ (at any given distance)? Getting faster, even by just a little bit, requires the biomotor ability of SPEED. In running, to increase speed, or reduce the time required to run a given distance, you must increase your stride rate or your stride length, or both. Increasing stride rate requires decreasing the contact time of your stance foot with the ground (for each stride). Increasing stride length requires a greater forward propulsive force (for each stride). Both of the variables of stride length and stride rate are dependent on force production. The biomotor ability that goes by the title of FORCE is ‘strength’. In cycling, we need to increase the force against the pedal to increase propulsive force. In swimming we need to increase propulsive force against ‘still’ water. (Finding the ‘still’ water is part of the skill component in swimming.)
In endurance sports, strength is the only biomotor ability that can result in greater average power and greater resistance to muscular fatigue over the length of the race.
Bompa and Haff, Periodization: Theory and Methodology of Training (2009)
Bompa and Carrera, Periodization Training for Sports (2005)
Friel and Vance, Triathlon Science (2013)