When pushing through a maximal effort during a heavy lift, some people briefly experience flashes of light or spots in their vision. This common occurrence is known medically as photopsia, and the specific flashes are called phosphenes. While the phenomenon is transient, it indicates a temporary disturbance in the visual system triggered by extreme physical strain. Understanding the underlying physiological process is key to preventing this experience.
The Physiological Explanation
The primary mechanism behind seeing stars during heavy lifting involves a rapid change in pressure within the torso and head. Many lifters instinctively employ the Valsalva maneuver, which involves taking a deep breath and forcibly exhaling against a closed windpipe to stabilize the core and spine. While this technique provides superior spinal bracing, the resulting increase in intrathoracic pressure has immediate effects on the circulatory system.
This sudden internal pressure severely restricts the return of venous blood from the lower body and head back to the heart. This restriction causes a temporary, systemic drop in blood pressure, known as hypotension, shortly after the strain begins or upon the release of the breath. When the pressure is released, the circulatory system attempts to immediately compensate, leading to a rapid pressure shift in the vessels supplying the brain and eyes.
The phosphenes are a direct result of transient vascular instability. The temporary reduction in blood flow, or ischemia, briefly starves the retina and the occipital lobe—the brain’s visual processing center—of oxygen. Visual cells, deprived of oxygen, misfire and send false signals to the brain, which are interpreted as flashes of light.
Preventing Visual Disturbances Through Proper Technique
Mitigating the chance of visual disturbances begins with abandoning prolonged breath-holding during sub-maximal lifts. Instead of relying on the full Valsalva maneuver, a structured breathing pattern should be integrated with the exercise movement. The general guideline is to inhale deeply during the eccentric, or lowering, phase of the lift, and to exhale steadily during the concentric, or exertion, phase.
For example, when performing a squat, you should inhale as you descend and exhale as you drive back up to the standing position. Maintaining this rhythmic breathing helps regulate intra-abdominal pressure, preventing the sharp, restrictive spikes that trigger the circulatory response. This controlled breathing pattern ensures a more stable supply of oxygen to the brain and muscles throughout the set.
Maintaining a stable blood pressure response also requires preparation outside of the lift itself. Ensuring proper hydration is important, as dehydration can exacerbate blood pressure fluctuations. Similarly, maintaining stable blood sugar levels by consuming a balanced pre-workout meal helps prevent hypoglycemia, which can compound lightheadedness and visual symptoms. Progressively increasing lifting weights allows the body time to adapt to the metabolic demands of heavy exertion.
When to Consult a Doctor
While seeing occasional phosphenes after a very heavy set is a common physiological response, certain symptoms warrant a medical consultation. If the visual disturbance persists for more than a minute or two after resting, seek medical attention. Phosphenes should not be a regular occurrence during light or moderate activity, as this suggests a possible underlying issue.
A doctor should be consulted immediately if the visual symptoms are accompanied by severe headaches, chest pain, or any loss of consciousness, known as syncope. These symptoms may signal a more serious cardiovascular or neurological event. Furthermore, if you notice an increase in “floaters”—small specks or clouds that drift across your vision—along with the flashes of light, it could indicate stress on the retina or vitreous gel, which should be evaluated by an eye care specialist.