However, research published in 2021 suggested that there was a positive causal relationship between ALS and intense physical exercise in those with a risk genotype. Sports
Both football and American football have been identified as risk factors for ALS in several studies, although this association is based on small numbers of ALS cases. A 2012 retrospective cohort study of 3,439 former NFL players found that their risk of dying from neurodegenerative causes was three times higher than the general US population, and their risk of dying from ALS or Alzheimers disease was four times higher. However, this increased risk was calculated on the basis of two deaths from Alzheimers disease and six deaths from ALS out of 334 deaths total in this cohort, meaning that this study does not definitively prove that playing American football is a risk factor for ALS. Some NFL players thought to have died from ALS may have actually had chronic traumatic encephalopathy (CTE), a neurodegenerative disorder associated with multiple head injuries that can present with symptoms that are very similar to ALS.Football was identified as a possible risk factor for ALS in a retrospective cohort study of 24,000 Italian footballers who played between 1960 and 1996. There were 375 deaths in this group, including eight from ALS. Based on this information and the incidence of ALS, it was calculated that the soccer players were 11 times more likely to die from ALS than the general Italian population.
Initial symptoms
The start of ALS may be so subtle that the symptoms are overlooked. The earliest symptoms of ALS are muscle weakness or muscle atrophy. Other presenting symptoms include trouble swallowing or breathing, cramping, or stiffness of affected muscles; muscle weakness affecting an arm or a leg; or slurred and nasal speech. The parts of the body affected by early symptoms of ALS depend on which motor neurons in the body are damaged first.In limb-onset ALS, the first symptoms are in the arms or the legs. If the legs are affected first, people may experience awkwardness, tripping, or stumbling when walking or running; this is often marked by walking with a "dropped foot" that drags gently on the ground. If the arms are affected first, they may experience difficulty with tasks requiring manual dexterity, such as buttoning a shirt, writing, or turning a key in a lock.In bulbar-onset ALS, the first symptoms are difficulty speaking or swallowing. Speech may become slurred, nasal in character, or quieter. There may be difficulty with swallowing and loss of tongue mobility. A smaller proportion of people experience "respiratory-onset" ALS, where the intercostal muscles that support breathing are affected first.Over time, people experience increasing difficulty moving, swallowing (dysphagia), and speaking or forming words (dysarthria). Symptoms of upper motor neuron involvement include tight and stiff muscles (spasticity) and exaggerated reflexes (hyperreflexia), including an overactive gag reflex. An abnormal reflex commonly called Babinskis sign also indicates upper motor neuron damage.