The discussion will include details about investigations that met the inclusion criteria for this review. Specifically, highlights of individual study methods, dosing, participants will be highlighted surround endurance exercise, anaerobic exercise (i.e., strength/power), recovery (i.e., DOMS), and metabolic markers. Following, conclusions are highlighted and synthesize the research to date as it pertains to the aforementioned specific areas.
Taurine and endurance exercise
The maintenance of taurine concentration in the muscle tissue might be important for enhanced endurance performance. Very few studies confirm the effect of acute or prolonged taurine ingestion on improving endurance performance in humans [2, 40, 51, 91]. However, trained individuals have higher taurine muscle content compared to their untrained counterparts, indicating a potential role of taurine in human endurance exercise performance [2, 26]. It can be speculated that since trained individuals typically have higher muscle taurine levels, supplemental taurine may be less effective and may have a lower level of enhancement in untrained subjects. Alternatively, higher doses of taurine may be required to achieve performance improvements. However, more research is needed to confirm this assumption.
There were no improvements in endurance performance treated with taurine in a low-intensity exercise protocol . Healthy active men and women ingested 1.66 g oral taurine 3x a day for 7 days. Subjects performed a 2 h cycling bout at ~ 60% peak oxygen consumption (VO2peak) after the 7-day ingestion period. There was no difference in muscle taurine content at rest (placebo, 44 ± 15 μmol/l vs. taurine, 42 ± 15 μmol/l) or after exercise (placebo, 43 ± 12 μmol/l vs. taurine, 43 ± 11 μmol/l). Taurine (1.66 g 3x a day for 7 days) did increase muscle content of amino acids (glutamate, aspartate, asparagine, and lysine) and had no effect on blood metabolites, heart rate, or respiratory responses (glucose, lactate, FFA, VO2, RER) to 120 min of exercise at ~ 60 VO2peak . The ingestion of a low dosage of taurine for 7 days, despite large acute changes in plasma following ingestion, does not support performance improvements or changes in carbohydrate metabolism .
The acute ingestion of 1 g of taurine (which was equivalent to 2.5 times the maximum daily quantity of taurine intake reported in normal human dietary analysis) 2 h prior to a maximal 3-km time trial performance in trained middle-distance runners significantly enhanced 3-km running performance . Subjects dietary intake 48-h before the performance session was recorded. This investigation was conducted in a simulated endurance performance assessment, more similar to real-world competitive endurance events than previous taurine ingestion studies.
Ten male competitive subjects received 6 g of taurine or placebo 120 min before a front-crawl maximal 400 m swim effort and resulted in no improvement pre-and and post-swim performance . However, it should be noted that plasma glycerol levels (lipolysis) pre and power were 8% higher for the taurine condition. Lactate concentrations were also lower in the taurine condition (11.4 ± 5.3%) compared to the placebo (14.2 ± 3.5%) . Swimmer performance was not statistically significant between the placebo and taurine conditions. Since the peak concentration of plasma taurine can be achieved 1.5 to 6 h post-ingestion, the maximal effort of the 400 m swim was performed within the peak concentration period (120 min) and could have promoted an additional effect on lipid metabolism-post exercise . This relationship between taurine’s timing, glycolytic system’s energy contribution, and performance improvement could play a role in lactate disappearance after exercise. Similarly, a 6 g dose of taurine consumed by recreationally trained males 90 min prior to completing a high-intensity exhaustive treadmill running test (110% VO2max) failed to show an improvement in endurance performance . Supplementation timing (90 vs 120 min) and exercise protocol design likely play significant roles in taurine’s ability to impact high-intensity endurance performance.
Little research is understood about taurine’s effects on high-intensity repeated sprint performance . Male university team sport players ingested 50 mg/kg dose of taurine supplementation 1 hour prior to three, maximal effort, 30s Wingate anaerobic capacity tests. However, taurine outperformed caffeine (5 mg/kg) and caffeine + taurine (5 mg/kg BM + 50 mg/kg BM) on performance changes. There was an increase in anaerobic performance compared to placebo, caffeine, or caffeine + taurine. Taurine elicited higher peak power, mean power, and mean peak power compared to caffeine + taurine and placebo . Taurine supplementation may increase performance improvements during short, high-intensity events. However, further research is needed to establish this effect and to reveal the underlying mechanisms that explain the current findings.
Time to exhaustion and VO2
An increase in running time to exhaustion has been shown to delay fatigue and increase endurance performance. Time to exhaustion running performance was investigated after participants were given a placebo, taurine (4 g/day), carnitine (4 g/day), or glutamine (4 g/day) tablets for 2 weeks . In the taurine condition, the subjects ran 6.9 min longer until exhausted on a treadmill at the intensity of 75% VO2max . Serum lactate concentrations measured 1 h after the initiation of the endurance exercise, as well as at an all-out state (immediately following cessation of TTE test) were decreased by taurine, carnitine, and glutamine supplementation. There were no significant changes detected in the lactate concentrations between the three conditions. However, taurine supplementation significantly reduced the serum inorganic phosphorus concentration measured at an all-out state (14% decrease, immediately following cessation of TTE test), assumingly preventing the accumulation in other organelles and continuing cross-bridge formation [1, 87]. Taurine significantly decreased serum ammonia concentration (32% reduction) during the time to exhaustion test . Taurine or carnitine supplementation (4 g/day) improved the time to exhaustion endurance exercise performance and related human fatigue factors.
Higher doses of taurine (4–6 g) in trained and untrained individuals compared to that of typical energy drinks (1–2 g) were investigated [78,79,80]. Male and female subjects consumed taurine (.5 mg/kg BM in capsule-form) 1.5 h prior to exercise; both groups performed different modalities (time-to-exhaustion trials, time-trials, end-test power output, and critical power output [78, 79]. The ingestion of capsule-form of taurine improved TTE endurance performance and critical power by a small amount, with larger effects found for TTE trials [79, 80].
An improvement in VO2max and TTE was seen in untrained men after frequent ingestion of 2 g, 3X a day . Endurance performance could possibly be improved to a similar magnitude after providing 1 g of taurine in a single oral dose or 6 g for up to 2 weeks [2, 51, 91].
Mixed aerobic exercise
The consumption of taurine was studied to support the emotional state and aerobic performance in soldiers . Soldiers consumed 250 ml of water with one of the following mixtures: 80 mg caffeine, 1000 mg taurine, 80 mg caffeine plus 1000 mg taurine, a commercial energy drink (Red Bull) or a placebo 10–15 min before a VO2max, time to exhaustion, strength (isometric strength), power (vertical jump), concentration (Grid test) and memory test (digits test). There was no significance among the commercial drinks, drinks with different bioactive compounds, and placebo in the various tests performed . However, peak taurine concentrations may not have been attained which could have affected the performance results [24, 30].
Taurine was investigated to evaluate the effects of oxidative stress, aerobic capacity, and maximal workload in untrained males . Subjects performed one VO2max test then received 2 g three times a day in a powder for 7 days prior to a second VO2max test. Taurine improved VO2max (43.7 ± 4.7 ml/kg/min vs. 46.7 ± 5.3 ml/kg/min), exercise time (18.8 ± 3.2 ml/kg/min vs. 19.3 ± 3.4 ml/kg/min), and workload (234 ± 65 W vs. 243 ± 67 W) after 7 days of supplementation. Even though there may have been familiarization between the two tests, taurine concentration levels were positively correlated with changes in time to exhaustion and maximal workload.
Cycling time trial performance
During a prolonged cycling bout in trained athletes, taurine’s ability to increase fat oxidation and performance in a subsequent trial was recorded . Male cyclists utilized a 1 h ingestion period followed by a further 1.5-h sub-maximal 90-min intensity ride before their cycling time trial . Subjects ingested 1.66 g of taurine or a placebo in beverage form. Differences in substrate oxidation between conditions were assessed in the intervening 2.5 h between ingestion and the start of the cycling time trial. Taurine (1.66 g) taken 1 h before 90 min of cycling at ~ 65 VO2max resulted in a small, but significant, 16% increase in total whole-body fat oxidation in endurance-trained men but no improvements in 90 min of cycling at 66.5% ± 1.9% VO2max . The dosing protocol was based on a previous study , and it should be reemphasized that plasma taurine kinetics peak at 90–120 min [24, 30]. However, their results did not explain the exact mechanisms responsible for the increase in total whole-body fat oxidation from taurine alone. Similarly, there was no effect on three, 4 km cycling time trial performance, VO2, lactate, pH, or HCO3− after consumption of 1 g (2 h prior to exercise bout) of taurine in endurance male athletes . Given the results of the aforementioned investigation on taurine and cycling time trial performance, it can be concluded at this time that taurine supplementation provides no time trial benefits; however, only two investigations have been conducted.
Thermoregulation and endurance exercise
Thermal strain (prolonged exercise in high environmental temperatures or humidity) negatively impacts performance . Amino acids have been shown to play a role in thermoregulation and the sweat response within the central nervous system during exercise.
The role of taurine in thermoregulatory control processes and improving time to exhaustion was examined in non-heat acclimated healthy male participants . Taurine supplementation (.5 g) 2 h before a cycling volitional time to exhaustion test in the heat (35 °C, 40% relative humidity) lowered core temperature and improved time to exhaustion by ~ 10%. Subjects cycled at the power output associated with their tested ventilatory threshold until absolute exhaustion. The subject’s core temperature (38.5 °C vs. 38.1 °C) was lower in the final 10% (taurine = 25.16 ± 5.25 min; placebo = 22.43 ± 4.28 min) of the time to exhaustion following taurine supplementation . Taurine supplementation increased time to exhaustion, mean sweat rate (12.7%), decreased RPE and core temperature, in the later stages of exercise, and reduced post-exercise blood lactate concentrations . This is likely due to taurine’s ability to improve thermoregulation, mechanical efficiency, and sweat response [31, 32, 51].
The sweat response from eccrine glands is governed by the thermoregulatory center in the hypothalamus which increases the sympathetic nervous system to increase sweat production . Taurine ingestion appeared to augment the sweat response by increasing the core temperature in the later stages of the bout. This response could elicit taurine’s role as a neuromodulator in the brain and serving as the amino acid gamma-aminobutyric acid (GABA) receptor agonist . Gamma-aminobutyric acid, a brain chemical, is widely distributed in the brain with high concentrations in the hypothalamus . It is considered the majority inhibitory neurotransmitter in most of the brain and also involved with thermoregulation . This brain chemical plays a central role in reciprocal inhibition between the effector pathways controlling thermoregulation . Taurine and GABA are both released from the hypothalamus, the main thermoregulatory center of the brain, suggesting taurine’s importance in temperature regulation [50, 51]. The accumulation of taurine in these central locations presumably reduces core temperature via taurine binding sites or antagonism of GABA receptors. These receptors are established effectors of hypothermia through distinct neural pathways . Higher plasma availability following ingestion of taurine is likely to cross the blood-brain barrier into these central areas, where it can interact with target receptors and prompt thermoregulatory responses. Given taurine’s capacity to cross the blood-brain barrier and elicit changes in time to exhaustion and mean sweat rate in the heat, shows taurine’s implications to assist with thermoregulation in sports performance and exercise. However, with the lack of evidence, more research is needed to elucidate taurine’s role in thermoregulation in sport and exercise.
Since taurine has protective redox actions on antioxidation, membrane stabilization, calcium flux, and thermoregulation, taurine was investigated to evaluate the effects of oxidative stress, aerobic capacity, and maximal workload in untrained males . Subjects performed one VO2max test then received 2 g taurine three times a day in a powder for 7 days prior to a second VO2max test. Taurine improved VO2max (43.7 ± 4.7 ml/kg/min vs. 46.7 ± 5.3 ml/kg/min), exercise time (18.8 ± 3.2 min vs. 19.3 ± 3.4 min), and workload (234 ± 65 W vs. 243 ± 67 W) after 7 days of supplementation. Even though there may have been familiarization between the two tests, taurine concentration levels were positively correlated with changes in time to exhaustion and maximal workload. Since taurine is found in greater concentrations in oxidative muscle fibers, this could suggest taurine could result in endurance exercise improvements . Improvements in endurance performance may be as a result of taurine’s role in calcium flux improving cross-bridge formation, as highlighted in the background of this review [17, 70, 71].
Conclusions on endurance
Outcomes related to taurine supplementation and endurance performance are largely mixed [14, 23, 35, 45, 63, 81]. Improvements in endurance performance may be as a result of taurine’s role in calcium flux improving cross-bridge formation [17, 70, 71].
Dosages vary (1 g – 6 g) in improving endurance performance in trained and untrained individuals [14, 45, 79, 91]. Single doses may be equally as effective as chronic loading periods to improve endurance performance without reaching taurine’s upper tolerable limit of 10 g/day [67, 80].
Since taurine is found in greater concentrations in oxidative muscle fibers, this could suggest taurine may improve endurance exercise performance . The enhancing effect of taurine on endurance performance may be a result of subjects utilizing more type I muscle fibers during aerobic events . However, there is little evidence of increasing endurance exercise. Prior taurine ingestion before endurance exercise may attenuate taurine losses from the muscle but it is inconclusive. Future research should investigate the effects of different doses of oral taurine supplementation across participants of varying ages, sex, health, and training status.
Taurine and muscle soreness
Previous studies have evaluated the effectiveness of branched-chain amino acid (BCAA) supplementation for preventing delayed onset muscle soreness (DOMS) and muscle damage induced by eccentric exercise [56,57,58, 68, 85]. Although taurine is not a BCAA, taurine could possibly delay muscle soreness by improving satellite cell activation and recovery after a single bout of high intensity, muscle-damaging exercise [10, 78, 79, 83]. Satellite cells are responsible for myofiber development, proliferation, differentiation, and renewal [10, 21]. Since taurine is found in high concentration in the skeletal muscle, after a high bout of exercise or injury, the myofibers are damaged resulting in disruption of the sarcolemma which causes the activation of satellite cells and release of taurine [2, 5, 10, 25, 66, 80, 86, 88].
Delayed onset muscle soreness is one of the symptoms of eccentric exercise-induced muscle damage and can result in prolonged loss of muscle strength, decreased range of motion, muscle swelling, and an increase of muscle proteins in the blood . Muscle damage is characterized as disruption of the membrane by mechanical stress, infiltration of inflammatory cells to the injured tissue, increase in creatine kinase (CK), increased production of inflammatory cytokines, and significant oxidant stress – each factor a potential target with taurine supplementation [56, 84]. As such, taurine is shown to mitigate DOMS. The protection against muscle soreness is of importance for strength improvements and performance adaptations. Taurine supplementation for 21 days (50 mg/kg/day) in male volunteers resulted in reduced CK levels and muscle soreness (DOMS) (lower than those of the placebo group on day 16 and day 18) . Taurine likely helps decrease the amount of muscle soreness during the recovery period. It is possible that the role of taurine lowering CK levels may assist in membrane stabilization and recovery .
Branched-chain amino acids and taurine were evaluated to prevent DOMS and muscle damage after eccentric exercise . Thirty-six untrained male subjects consumed 2 g of taurine or a placebo 3X a day (6 g/day) after every meal for 2 weeks prior to exercise and 3 days after eccentric elbow flexor exercises (6 × 5, 90% maximal voluntary contraction (MVC) . A combination of 3.2 g BCAA and 2 g taurine, three times a day, 2 weeks prior to an eccentric exercise (ECC) bout, and 3 days after, attenuated some markers of DOMS (visual analog scale (VAS)) and muscle damage (serum levels of LDH, 8-OHdG, CK) levels induced by high-intensity eccentric exercise (ECC). However, there was no effect of prolonged taurine use, without the combination of BCAA, on soreness or markers of muscle damage caused by eccentric elbow flexion exercise in untrained men . It appears that the combination of BCAA and taurine is essential to mitigate muscle soreness effects and muscle damage induced by high-intensity ECC.
In a follow-up study, recreational trained subjects used an identical taurine supplementation (2 g of taurine, independent BCAA, or a placebo powder 3x a day after meals for 2 weeks before ECC elbow flexion exercise (2 × 20, MVC) . Supplementation was continued until the third day after exercise. Muscle soreness during a 4-day recovery period after exercise was attenuated in the participants who consumed taurine . Multiple ingestions of taurine supplementation throughout the day significantly reduced the severity of DOMS induced by ECC.
Similarly, taurine (0.1 g) over 3 days following eccentric exercise attenuated the rise in serum creatine kinase and improved performance recovery in recreationally trained males . Subjects performed 60 eccentric contractions of the biceps brachii at maximal effort. Following the exercise bout, participants were supplemented with 0.1 g/kg/bodyweight of either taurine or rice flour in capsules, morning and evening. Neither treatment group fully recovered force output by 72 h over time or between treatments. However, force recovery significantly increased toward pre-values at 48 h with taurine compared to placebo . Taurine may expedite the recovery of eccentric force. The source of the increased taurine plasma content after exercise requires further exploration as this may reflect muscle soreness and force output. Taurine supplementation shows promise as a nutritional adjunct to reduce symptoms of exercise-induced does, though more information is needed to determine optimal dosing patterns.
Taurine and strength and power
Eccentric actions are characterized by a high force output which is performed in pre-season sports to increase strength and power in the later seasons [8, 9]. Since taurine assists the SR with Ca2+ release, this increases the sensitivity of force-generating myofilaments, in both skeletal muscle and cardiac tissue [17, 70], increasing muscle force  and thus improving performance outcomes. Even though taurine’s role in endurance performance is more conclusive, research is limited in taurine’s role to increase strength and power. However, the degree of muscle soreness may affect strength improvements and force outputs; taurine may be able to modulate these effects.
Improvements in strength and power with taurine supplementation were notable [12, 41, 78, 79, 83]. The degree of muscle soreness may affect strength improvements and force outputs. The effects of taurine (0.5 g/kg/body mass/day for 21 days) improved concentric and isometric strength during the 48 h after elbow flexion exercise (3 × 11–15, 80% 1RM) in male students . Taurine effectively enhances concentric and isometric strength during the recovery period after exercise. For athletes who perform subsequent training bouts per week during a training season, taurine may be beneficial to improve strength. Increasing strength is important to increase power output . The ability of taurine to affect muscle function and power output in caffeine and caffeine-deprived users were examined . Trained male athletes (who were separated into caffeine and non-caffeine users) ingested a placebo (10 mg/kg body mass) or capsules (40 mg/kg/ body mass of taurine) with 250 mL of water 1 hour prior to four isokinetic or three maximal isometric knee extensions. Taurine ingestion did not affect maximal voluntary muscle power, maximal isokinetic, and isometric peak torque in noncaffeine consumers, whereas taurine ingestion in caffeine-deprived, caffeine consumers improved maximal voluntary muscle power (isokinetic peak torque, isometric peak torque, and isokinetic power). There was no effect on other aspects of contractile performance . Thus, taurine can play a role in isokinetic peak torque, isometric peak torque, and isokinetic power in caffeine-deprived users. This study has important implications for habitual caffeine users wishing to ingest taurine.
Most of the available studies available have focused on taurine’s ability to affect power output in men. However, to our knowledge, one study investigated women’s power output . Female university lacrosse players ingested taurine (50 mg/kg body mass) + maltodextrin (3 g/kg body mass) or placebo (.3 g/kg body mass maltodextrin) 1.5 h prior to a cycling ramp test fixed in the isokinetic mode (90 or 50 cadences) until exhaustion. There was an effect of higher end-test power with taurine compared to placebo. There was no difference in ramp exercise or sprint performance, but taurine ingestion is responsible for an increase in ramp exercise and end-test power output . Although the reasons were unclear, taurine likely plays a role in skeletal muscle contraction function and power output. Females competing in short, aerobically based cycling, may benefit from taurine to produce a greater end-test power output as fatigue starts to increase. In a subsequent study, critical power in men was analyzed . Critical power represents the highest power output that can be maintained for a duration of time, without a continuous rise in VO2 and blood lactate concentrations or reductions in phosphocreatine stores . Critical power can be used to assess training status, performance improvements, or the power-time relationship . Taurine is speculated to alter the power-time relationship. Untrained men consumed a taurine capsule (0.5 g/kg/BW) or a placebo (0.3 g/kg/BW) 1.5 h prior to a 3-min all-out test (3MAOT) or a TTE test at a fixed external power output 5% greater than their baseline critical power 3MAOT. There was an improvement during the 3MAOT, peak power, and TTE with taurine supplementation . Taurine could improve TTE and critical power outputs in untrained men. However, the effects of taurine were more effectively demonstrated in the TTE test. This is likely due to a greater concentration of taurine in oxidative muscle fibers . Acute taurine supplementation is shown to increase exercise tolerance and critical power output in men, and end-test power out in women. However, to our knowledge, no peer-reviewed literature exists on taurine’s independent role in skeletal muscle hypertrophy. To date, the experimental evidence on fiber cross-sectional area or muscle mass is lacking. Since taurine is known to increase strength and power as well as improve muscle repair from injury, we can only theorize that taurine must play a role in hypertrophy. The relationship between taurine supplementation and skeletal muscle hypertrophy warrants further investigation.
Dietary protein intake
Since taurine is found primarily in animal products , concentration levels of taurine via the diet can potentially confound taurine supplementation. As such, it is vital to account for a subject’s baseline taurine levels prior to supplementing with additional taurine, as drastically different levels could confound results. It can be assumed that individuals who eat a higher protein diet will likely have higher taurine and amino acid levels in the muscle. The use of these amino acids is important for such pathways as cAMP/PKA  and thermoregulation . Thus, if there is a higher concentration of taurine, it may improve the function of these pathways and ultimately sport and exercise performance.