On a long ride, the first sign of fatigue is not always a falling average speed. Sometimes it is the growing effort required to stay comfortable on the bike. The hands keep changing position. The shoulders rise. A posture that felt unremarkable in the first hour begins demanding attention in the fourth. Running has its own version: the legs are still moving, but holding a familiar rhythm starts to feel less automatic.
These changes have several possible causes, including pacing, equipment fit, fueling and the fatigue of the working muscles. They cannot be diagnosed as a weak core from a photograph or a tired feeling. But they reveal something useful about endurance: continuing to produce force and continuing to organize the body around that force are related tasks. Aerobic fitness helps sustain the work. The trunk helps manage the positions and movements through which that work happens.
Core strength for endurance athletes matters within that relationship. Its value comes from developing enough strength, endurance and control to meet the demands of the sport, including the demands that appear after several hours. Understanding those different capacities makes core training more useful—and makes some of its familiar promises easier to question.
Building stability that carries into movement
A strong core combines several capacities: producing force, managing movement and sustaining muscular work. The core muscles include the abdominal muscles and the muscles around the sides and back of the trunk. The deep core muscles contribute alongside larger muscles; the stabilizer muscles do not operate as a separate system that needs a special switch. Together, they help coordinate the rib cage, pelvis and lower back as the limbs move. This makes core stability a task-dependent ability: supporting a cycling position requires a different response from controlling the body during an uneven trail landing.
Simple bodyweight exercises provide a practical starting point for building stability. A dead bug challenges control as an arm or leg moves away from the body. A side plank introduces a sideways loading demand, while a modified plank performed from the knees reduces leverage so the athlete can practise manageable support. These core exercises develop strength and stability through different demands. Useful core engagement means applying enough muscular effort to control the exercise while continuing to breathe. Progress comes from gradually increasing reach, resistance or duration while preserving that control.
Athletes often begin this work hoping to improve posture or prevent injury. Those goals require a wider view. Rounded shoulders after hours on the bike do not, by themselves, establish weakness, and no abdominal routine guarantees protection from injury. Postural stability means being able to manage and change position under the demands of the task. For athletic performance, trunk work belongs alongside full-body strength, appropriate endurance training and recovery. Its contribution to sports performance should be judged through both improving exercise capacity and the athlete’s ability to tolerate the movements their sport requires.
The trunk has several jobs at once
The word “core” often brings to mind the muscles visible across the front of the abdomen. In movement, the working system extends around the sides and back of the trunk and interacts with the pelvis, hips and rib cage. The abdominal muscles, spinal muscles and breathing muscles contribute in different ways. There is no single muscle that can be switched on to organize the whole arrangement.
It helps to separate three qualities. Strength is the ability to produce force. Endurance is the ability to sustain or repeat muscular work. Control is the ability to coordinate that work for a particular task. A runner might hold a plank for a long time yet struggle with a demanding loaded exercise. Another athlete might lift a heavy weight but find a modest side plank unexpectedly difficult. Neither result describes the entire system.
An engineering view starts with the forces acting on a structure and the movement it must allow. The body adds another requirement: it has to adjust continuously. When one foot meets the ground, the trunk participates in managing the resulting motion. When a cyclist pulls on the bars during a steep climb, the upper body and pelvis help organize the effort. When a swimmer reaches forward, the trunk coordinates with the shoulders and hips as the body rolls.
In each case, stability means controlling movement sufficiently for the task. Some movement is necessary. Running includes rotation, cycling positions change with terrain and effort, and swimming depends on coordinated body roll. Training should expand the athlete’s ability to manage these movements rather than teach a single rigid posture.
Why more movement does not automatically mean wasted energy
“Energy leakage” is an appealing explanation for core training. It suggests that a weak trunk allows effort to escape and that strengthening it will send more power directly into the ground or pedals. The phrase is easy to remember, but it conceals the mechanics.
Muscles create forces around joints. Those forces can produce movement, resist movement or balance other forces. In a band exercise that pulls the hands sideways, the band creates a turning effect on the body. The farther the hands move from the trunk, the greater the turning demand can become. Keeping the pelvis facing forward requires the athlete to manage that demand through the trunk, hips and contact with the floor. The exercise becomes harder for a clear mechanical reason, even if the band itself has not changed.
Sport is less tidy. A runner’s arm swing helps manage the rotational effects of the legs. The pelvis and trunk move as part of the stride. Eliminating visible rotation would not necessarily make that runner more economical. Likewise, a cyclist moving the bicycle beneath the body while climbing out of the saddle is not automatically wasting effort.
The useful question is whether an athlete can control the movement the task requires without unnecessary effort or an early loss of capacity. A stronger trunk may help when trunk capacity is a limitation. It will not correct every technical habit, compensate for an unsuitable bike position or turn every visible asymmetry into a performance gain.
What the research can actually tell us
Core training studies offer reasons to include the work, alongside reasons to keep expectations specific. In a small study by Sato and Mokha, 20 runners completed a six-week investigation. The group assigned core training improved its 5,000-metre performance relative to the control group, but the researchers did not find significant improvements in the measured ground-reaction forces or lower-limb stability. The performance result was encouraging; the proposed mechanical explanation remained unresolved. Research: Sato and Mokha, 2009
Other findings show why a better core test cannot be treated as a guaranteed faster race. Stanton and colleagues studied 18 young male athletes and found that six weeks of Swiss ball training improved their core stability measure without improving running economy. Hung and colleagues later studied 21 male college athletes and reported improved core endurance and lower oxygen consumption at the highest tested treadmill stage after eight weeks of additional core training. These are small studies in particular populations, with different exercises and outcomes. Research: Stanton et al., 2004; Hung et al., 2019
A reasonable practical interpretation is that trunk capacity is trainable, while its contribution to endurance performance depends on the athlete and the task. Someone whose trunk capacity is already sufficient may gain little race performance from additional planks. Someone who has rarely trained the trunk directly may have more room to improve. Neither athlete can assume that a percentage increase in a laboratory hold will produce the same percentage improvement in speed.
This distinction also matters when reading broader research on strength training. Evidence that heavy resistance training or plyometrics can improve running economy does not establish that an abdominal circuit produces the same adaptation. Our wider guide to strength training for endurance athletes considers how different forms of strength work fit together. Core training has a place within that program, alongside the strength of the legs and upper body.
Fatigue changes the demands on the system
Early in a session, a familiar movement may sit comfortably within the athlete’s available capacity. As fatigue develops, maintaining the same task can become more demanding. The athlete may change position, recruit muscles differently or adjust the movement. Some adjustments are useful responses. Others may indicate that the current task is becoming difficult to sustain.
A cycling study by Abt and colleagues makes this relationship tangible. After a trunk-fatiguing workout, 15 competitive cyclists showed changes in knee and ankle movement during a subsequent cycling test. Measured pedal forces did not change significantly. The experiment showed that induced trunk fatigue could alter cycling mechanics; it did not demonstrate that a core program would increase power, prevent injury or reproduce a particular benefit over a long ride. Research: Abt et al., 2007
For an athlete, the practical interest is the ability to manage a position or movement as the day progresses. On the bike, that might involve remaining comfortable enough to use the intended riding position. On a trail, it includes organizing the body around uneven foot placements while attention and muscular capacity are being taxed. Trunk training can address part of that preparation, while riding and running remain essential for learning the actual demands.
This is also why late-session discomfort deserves a wider investigation. A cyclist repeatedly shifting on the saddle may need a position adjustment, a change in training load or more frequent movement breaks. Adding a harder core circuit without examining the cause can create more fatigue while leaving the original problem in place.
Breathing belongs inside the movement
Endurance creates a requirement that a brief strength effort can sometimes avoid: the athlete has to keep breathing while managing force. The diaphragm contributes to breathing and also participates in postural tasks. Laboratory research has shown that its postural activity changes when respiratory demand is increased, illustrating that these functions have to be coordinated. That finding does not prove that a particular breathing drill improves race performance, but it helps explain why trunk training should account for breathing. Research: Hodges et al., 2001
Consider a side plank. An athlete may hold a difficult version for twenty seconds by tightening everything and holding their breath. That demonstrates an ability to tolerate the position briefly. Choosing a slightly easier version and taking several controlled breaths asks a different question: can the athlete maintain sufficient support while the rib cage continues moving?
For supporting endurance work, that is often a useful progression. Establish a manageable position, keep breathing and gradually increase the mechanical demand. During the sport itself, the aim is to let trained coordination operate without consciously squeezing the abdomen through every kilometre. Constant maximal bracing would make a long run an unnecessarily demanding exercise in tension.
What instability adds—and what it costs
An unstable exercise changes the control problem. On the floor, the contact points of a push-up remain fixed. With the hands in rings, each support can move, so the athlete must manage the rings as well as raise and lower the body. Changing the body angle, foot position or range of motion changes the difficulty further.
This makes instability a useful training variable, but the trade-off matters. Research comparing stable and unstable conditions has shown that instability can reduce the force an athlete produces. A demanding sensation therefore does not necessarily mean a greater strength stimulus for the main working muscles. Stable loading and unstable loading can serve different purposes. Research: Behm et al., 2002
At MARMATI, strength through instability means using that control demand deliberately. For example, an inclined ring push-up with the feet on firm ground can provide a manageable introduction to moving supports. The athlete can adjust the angle to retain control rather than chase the greatest possible shaking. The connection between suspension work and broader training is explored further in why gymnastic rings belong in an endurance athlete’s kit.
A trail does not have to be imitated by placing every strength exercise on an unstable surface. Running on trails provides its own highly specific practice. Supporting training can develop capacities separately: higher force on stable ground, controlled responses to moving supports, and gradual exposure to the terrain itself. The athlete benefits from having several options available.
Adaptation needs progression, not constant novelty
Repeating an exercise makes the athlete more familiar with its coordination demands. Over time, appropriately challenging training can also increase muscular strength and endurance. Those changes depend on the stimulus and recovery. Simply performing the same easy sequence indefinitely may preserve familiarity without creating much further adaptation.
The progression can be small and measurable. A side plank can move from bent knees to straight legs. A controlled dead bug can use a longer reach. A band press can use slightly more tension or a longer pause with the arms extended. These changes increase the demand without requiring a different workout every week. They also make progress easier to judge: the athlete can compare the same task under similar conditions.
A modest session may feel easy to the lungs of an experienced endurance athlete while still presenting unfamiliar loading to the trunk, shoulders or hips. Aerobic fitness does not guarantee readiness for every strength exercise. Begin with a dose that leaves the next few days of training workable, then build from the response.
Equipment is useful when it makes that progression and consistency easier. A RAWBAND™ resistance band can provide a sideways pull for a standing press without a cable machine. A pair of gymnastic rings can provide adjustable pushing and pulling exercises during travel, given a suitable anchor. Both can support several movements as the athlete progresses.
That range of use also matters in product design. An adjustable tool can remain useful after the first exercise becomes easy, reducing the need to replace it with another fixed-purpose object. It still requires inspection and care: rubber ages, webbing wears and hardware needs checking. Durability comes from the relationship between material, construction, loading and maintenance, rather than a promise that equipment lasts indefinitely.
How to build core training into an endurance week
Start with two short sessions of core exercises each week, preferably within strength sessions you already perform. Around ten to fifteen minutes is a practical starting allocation, rather than a proven minimum dose. Choose three core exercises you can perform well and repeat them long enough to assess progress and improve core muscles. The following sequence of bodyweight exercises is a starting example for an athlete without a current injury or exercise restriction.
Begin with a dead bug. Lie on your back with the hips and knees bent and the arms reaching upward. Slowly lower one heel toward the floor, then return and alternate sides. Use a range in which you can manage the trunk position without a large, uncontrolled change in your back arch. Start with two sets of five to eight repetitions per side. As control improves, lengthen the leg reach or add the opposite arm. Keep the movement slow enough to notice what changes.
Add a side plank. Support yourself on a forearm, with the elbow beneath the shoulder, and begin with the knees bent if needed. Lift the hips into a manageable position and continue breathing. Start with two holds of fifteen to twenty-five seconds per side, resting between efforts. End the hold when you can no longer maintain the intended position. Progress toward straight legs before accumulating very long holds. The shoulder supports part of the load, so choose a version of side plank it can tolerate comfortably.
Finish with a standing band press that resists rotation. Secure a light band at approximately chest height and stand sideways to the anchor on firm ground. Hold it at the chest, then press the hands forward while keeping the pelvis and chest facing ahead. Pause briefly and return. Start with two sets of six to ten repetitions per side. Use a secure anchor and enough tension to require attention without pulling you out of position. A controlled return matters as much as the press.
Allow roughly thirty to sixty seconds between sets, or longer when needed to repeat the movement well. These exercises cover controlling the trunk as the limbs move, resisting a sideways bending demand and resisting a turning demand. They are useful starting tasks, rather than a complete representation of running, cycling or swimming. Your wider program should still include appropriate lower-body work and upper-body pushing and pulling.
For the first few weeks, keep the dose fairly consistent. When the upper end of the repetition or hold range becomes manageable, change one variable: reach farther, use a harder leverage position or add a small amount of resistance. You should be able to describe how the exercise became harder. Shaking, soreness and exhaustion are poor substitutes for that record.
Place demanding or unfamiliar work where it is least likely to degrade an important endurance session. For many athletes, that means keeping it away from the day before a long race-specific workout and completing it after, rather than before, the day’s priority training. The broader scheduling decisions are covered in hybrid training without compromising endurance.
Assess two things over the following weeks: whether capacity in the exercises improves and whether the training remains compatible with riding, running or swimming. Changes in late-session comfort or control may be worth recording, but weather, pacing, fueling and training load also influence them. A longer plank is a clear improvement in that task. A faster race requires a wider explanation.
The useful outcome is a body with more capacity available for the situations endurance brings: holding a position, changing direction, reaching for a bottle, carrying equipment or responding to an awkward step. Core training earns its place when it contributes to those tasks at a recoverable cost. On a long day outside, that preparation may be noticed simply as having fewer reasons to interrupt the movement.
Frequently asked questions
Does core training improve running economy?
It may help, but results are mixed. Small studies have reported improvements in some running measures, while others have improved core stability without improving running economy. Core training is best used as part of a wider program, with expectations based on the athlete’s needs. Research: Hung et al., 2019; Stanton et al., 2004
How often should endurance athletes train their core?
Two short sessions per week are a practical starting point. The appropriate dose depends on exercise difficulty, existing strength work and the endurance calendar. Progress only while the work remains compatible with key sessions and recovery.
Are planks enough for cyclists and runners?
Planks are useful for training particular holding tasks. A broader selection can also challenge the trunk while the limbs move, resist rotation and develop capacity through different positions. Keep appropriate leg and upper-body strength work in the program.
Is unstable core training better than training on the floor?
Its value depends on the goal. Moving supports add a control demand, while stable supports generally make higher force production easier. Use an unstable exercise when that control challenge is useful and manageable, then progress it deliberately. Research: Behm et al., 2002
Should I brace my core while running?
Avoid deliberately holding a maximal abdominal contraction throughout a run. The task requires ongoing breathing and coordinated movement. Practice controlled trunk work in training, then allow your running to remain responsive rather than trying to hold a rigid position.
