Is Post-Exercise Muscle Soreness Due to Lactic Acid Buildup? Four Ways to Distinguish Soreness from Injury

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Many people experience muscle soreness after exercising. But why does this happen? Many believe that muscle soreness is a sign of effective training. Is that true? In reality, soreness might not be what you think.

Muscle Soreness Isn't Due to Lactic Acid Buildup and Is Unrelated to Training Effectiveness

Post-exercise soreness is common, affecting everyone from professional trainers to beginners. A few hours to a day or two after intense activity, the muscles that were heavily used may become sore. For example, your legs might feel heavy after cycling, or the targeted muscles may be sore after weight training. This is known as delayed onset muscle soreness (DOMS).

DOMS differs from the soreness experienced during exercise. For instance, during weight training, a set of 8-10 reps might induce fatigue, indicating sufficient muscle stimulation. However, post-exercise soreness isn't directly related to muscle growth.

Lin Xingqing, deputy secretary-general of the Taiwan Society of Sports Medicine, explains that post-exercise soreness may indicate muscle fiber damage or injury. While the body initiates self-healing to repair muscle fibers, leading to muscle growth, there's no evidence that soreness itself promotes muscle gain. Smart trainers avoid pushing themselves to the point of soreness, as it can hinder subsequent training sessions and daily activities. Many mistakenly believe that lack of soreness means ineffective training, leading to increased intensity and duration in future sessions, which increases the risk of injury.

It's a common misconception that post-exercise muscle soreness is due to lactic acid buildup. Professor Hou Jianwen from the Department of Exercise Science at the University of Taipei points out that while ATP (adenosine triphosphate) production during exercise does produce lactic acid as a byproduct, research shows that lactic acid levels in the blood decrease significantly within five minutes after exercise and are completely cleared after 15 minutes, so it doesn't cause next-day soreness.

On the contrary, lactic acid is a valuable energy source. The body can recycle lactic acid to produce energy. The real culprit is hydrogen ions produced during lactic acid metabolism. These acidic ions accumulate in muscles, impairing waste removal efficiency and causing soreness. The body can't quickly eliminate hydrogen ions, leading to DOMS.

Thus, various factors contribute to post-exercise muscle pain. Apart from the inflammatory response due to slight muscle fiber damage, Hou Jianwen explains that nerve growth and tissue connection during repair also contribute to the sensation, unrelated to lactic acid.

Three Methods Besides Muscle Fiber Damage to Increase Muscle Mass

Muscle fiber damage releases inflammatory substances, triggering the body's repair mechanism to strengthen tissues, which leads to muscle growth. However, muscle gain isn't solely dependent on fiber damage.

Lin Xingqing highlights that muscle growth can also result from mechanical tension and metabolic stress:

1. Mechanical Tension: Muscle growth stimulated by weight

2. Metabolic Stress: Hormonal and endocrine changes in response to weight stimulus

Achieving one or two of these methods can promote muscle growth without causing soreness. For instance, Olympic athletes often use blood flow restriction training, which involves using bands to alter blood flow, tricking the body into thinking it's in a harsh environment and needs more muscle and blood. This method can increase muscle mass using only 20-40% of typical weights with minimal DOMS, demonstrating the effectiveness of combining mechanical tension and metabolic stress.

Lin Xingqing also notes that using appropriate weights and sets, typically 8-12 RM, is efficient for muscle growth without causing significant soreness.

How to Distinguish DOMS from Exercise Injury? Five Tips to Relieve Soreness

Soreness is often associated with exercise injury. How to tell the difference? Lin Xingqing offers these distinctions:

1. DOMS appears 1-3 days post-exercise; injuries can occur immediately.

2. DOMS lasts about 3-5 days; injuries may last longer.

3. DOMS doesn't typically involve obvious inflammation (redness, swelling, heat, pain); injuries do.

4. DOMS doesn't significantly limit movement; injuries might cause severe pain or restricted movement.

While DOMS isn't harmful to long-term health, it can affect daily activities. Lin Xingqing advises that simple stretching post-exercise doesn't significantly alleviate soreness. Here are five proven methods to reduce soreness:

1. Massage: A 20-30 minute massage two hours post-exercise can ease DOMS.

2. Compression Garments: Wearing pressure clothing like compression tights post-exercise reduces tissue swelling and increases venous return, helping to reduce fatigue and DOMS.

3. Cold Water Bath or Contrast Bathing: Alternating between cold and warm water baths.

4. Low-Intensity Aerobic Exercise: "Active recovery" such as light cardio can reduce soreness and promote recovery. This can be combined with foam rolling and stretching.

5. Anti-Inflammatory Medications and Physical Therapy: If soreness is severe, anti-inflammatory drugs or physical treatments like electrical therapy can alleviate symptoms.