Protective effects of lactic acid on force production in rat skeletal muscle

Abstract

During strenuous exercise lactic acid accumulates producing a reduction in muscle pH. In addition, exercise causes a loss of muscle K+ leading to an increased concentration of extracellular K+ ([K+]o). Individually, reduced pH and increased [K+]o have both been suggested to contribute to muscle fatigue. To study the combined effect of these changes on muscle function, isolated rat soleus muscles were incubated at a [K+]o of 11 mm, which reduced tetanic force by 75 %. Subsequent addition of 20 mm lactic acid led, however, to an almost complete force recovery. A similar recovery was observed if pH was reduced by adding propionic acid or increasing the CO2 tension. The recovery of force was associated with a recovery of muscle excitability as assessed from compound action potentials. In contrast, acidification had no effect on the membrane potential or the Ca2+ handling of the muscles. It is concluded that acidification counteracts the depressing effects of elevated [K+]o on muscle excitability and force. Since intense exercise is associated with increased [K+]o, this indicates that, in contrast to the often suggested role for acidosis as a cause of muscle fatigue, acidosis may protect against fatigue. Moreover, it suggests that elevated [K+]o is of less importance for fatigue than indicated by previous studies on isolated muscles.

Expiratory muscle fatigue impairs exercise performance

“…leg exercise) via an increase in blood lactate (up to 10 mmol l ¡1 ), resulting in reduced performance (Bangsbo et al 1996;Hogan and Welch 1984;Jacobs et al 1993). However, recent studies have shown that muscle performance is enhanced rather than impaired by higher lactate concentrations (Nielsen et al 2001;Pedersen et al 2004). Moreover, in a previous study we did not observe a signiWcant increase in blood lactate concentration as a result of inspiratory resistive breathing at 70% PI max to exhaustion (Rohrbach et al 2003).…”

Carbohydrate metabolism in meat animals

“…The activation of glycogen phosphorylase during stress increases the accumulation of lactate and protons and changes ion permeability causing fatigue, and ultimately, pain and distress (Gregory, review 1998;Nielsen, de Paoli, & Overgaard, 2001;Pedersen, Nielsen, Lamb, & Stephenson, 2004). The acidification of the muscles causes changes in ion balance which leads to attenuation of the rate of glycolysis, because protons inhibit the activities of glycogen phosphorylase and phosphofructokinase and thus energy production from carbohydrates (Fitts, review 1994;Nielsen, de Paoli, & Overgaard, 2001;Pedersen, Nielsen, Lamb, & Stephenson, 2004). Protons may also inhibit the function of myosin ATPase (Fitts, review 1994;Schiaffino & Reggiani, review 1996) and thus impair muscle contractions.…”

Effects of pomegranate juice in circulating parameters, cytokines, and oxidative stress markers in endurance-based athletes: A randomized controlled trial

“…with lactate against muscular fatigue [32]. It must take in account that a bottle of PJ contains while MDA levels were not affected after four weeks of pomegranate juice consumption [19].…”