Lactate Threshold and Testosterone

Written by Ben Bunting: BA(Hons), PGCert. Sport & Exercise Nutrition. British Army Physical Training Instructor.  

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A recent study published in the Journal of Physiology investigated the relationship between lactate threshold and testosterone levels.

In particular, it studied the effects of exercise on the body's hormone levels and how these responses are affected by the duration of the activity.

It found that endurance exercise, such as walking, may have a positive effect on the male sex hormone.

Lactate explained

Lactate is the ultimate end product of glucose utilisation and is transported into the bloodstream via active transport by muscle fibres.

The liver converts lactate into glucose and pyruvate and fuels the Krebs cycle, while the blood transports these into the skeletal muscle. This leads to an increase in lactate concentration.

Since strong ion gap (SIG) reflects acid-base imbalances, an abnormally high SIG can be explained by elevated lactate concentration.

Until recent decades, it was thought that lactate production was a major cause of muscular fatigue during exercise.

Early studies revealed that lactate increased in both the blood and muscle tissue, and this correlated with levels of fatigue. But the mechanism underlying this increase is still not fully understood.

One hypothesis is that increased lactate is a result of the activation of phosphofructokinase (PFK), which enhances glycolysis. PFK then facilitates the conversion of glucose into lactate.

PFK has also been associated with the increased sensitivity to alkalosis, which increases the production of lactate. PFK is activated when mitochondrial oxidation is impaired by an increase in alkalinity, which may inhibit the activity of the mitochondrial oxidative enzyme, the Krebs cycle.

Lactate levels in the blood are typically between 1 and 2 mM. Blood lactate is an indirect marker for the biochemical events that occur during exercise, and during the rest period.

Lactate threshold explained

The lactate threshold is an intensity level where lactate builds faster than the blood can clear it. This causes the athlete to experience burning sensations and cramps.

Lactate is produced by the liver and is used by the body as fuel. However, high levels can cause performance to suffer. Therefore, it's important to train to clear it from the blood.

Lactate threshold is used as a determinant of exercise intensity and as a training benchmark. It is also helpful for tracking fitness gains.

To measure lactate threshold, a chest strap heart rate monitor is required. A test is performed by increasing the resistance on the trainer by 20 watts every two minutes.

Blood lactate concentration is also measured during a VO2max test. A 30-minute time trial is the most accurate method to measure running velocity.

Lactate threshold is a term that has become common in endurance sports. In fact, elite athletes often use the term in their training routines to help them achieve success.

However, there are still many questions about how to improve lactate threshold. This is because the science is subject to ongoing debate. 

Lactate is produced when glucose is broken down by the liver and the muscles. Lactate is also used as a fuel by the heart and the kidneys. Because of this, a higher lactate threshold is more beneficial for performance. 

Aerobic exercise and lactate

Aerobic exercise has been shown to increase lactate threshold and testosterone in the short term.

The intensity of exercise is likely to affect the hormone changes. However, the relationship between exercise intensity and hormone concentrations has not been fully investigated.

A number of studies have been conducted to address this question, but the results are inconclusive.

In addition to the increased levels of lactate and testosterone, aerobic exercise has been shown to have an effect on the metabolic clearance of anabolic hormones. 

One study investigated the effects of a 12-week aerobic exercise intervention on circulating serum testosterone concentrations in overweight/obese men.

Testosterone was measured before and after the exercise session. After the session, serum testosterone levels remained elevated for 48 hours.

Another study evaluated the effect of 24-weeks of moderate-intensity exercise on basal testosterone and growth hormone concentrations in healthy, lean individuals.

Plasma total protein, growth hormone, cortisol, and estradiol were also measured. They found that the effects of the 24-week intervention were similar to those of a 16-week aerobic training program.

Finally, there have been additional promising studies examining the effect of exercise on growth hormone in older men. Growth hormone levels are typically lower in obese and elderly men.

It is possible that the low baseline testosterone in these groups may be due to low luteinizing hormone and follicular-stimulating hormone levels.

However, these studies do not have enough data to determine the exact molecular mechanisms.

Future studies should also focus on the downstream effects of the testosterone release. This would help to understand how testosterone affects muscular adaptation and hypertrophy.

Animal study

An increase in plasma testosterone after a short bout of swimming may be due to a direct effect of lactate on the secretion of testosterone, or to an increase in testicular cAMP production.

Another possible mechanism is that increased lactate causes a rise in GnRH (gonadotropin-releasing hormone).

The effects of exercise on testosterone secretion are still unclear. A recent study in rats investigated the acute effects of lactate on testosterone production in rat Leydig cells.

It found that incubation of a metabolite with Leydig cells increased testosterone production.

In vitro studies have also shown that pyruvate enhances testosterone secretion.

Despite the lack of evidence for this effect in humans, more research is needed to determine whether the combination of aerobic-resistance exercise can increase both cortisol and testosterone secretion.

Testosterone is an important steroid involved in muscle adaptation and is antagonistic to cortisol. It interacts with anabolic signaling pathways, such as b2-adrenergic receptors in the mouse testes.

Among the factors affecting testosterone secretion are intensity, duration, volume, and rest.

A previous study in humans suggests that cortisol can reduce the ability of a person to release free testosterone. This may be because of the influence of the adrenal cortex in the body.

Does testosterone affect lactate levels?

The circulating level of testosterone in the blood increases following exercise. It is thought that lactate plays a role in stimulating the release of testosterone through the mTOR pathway. However, this may depend on the type of exercise and the time.

In one study, testosterone and pre-albumin were measured at different times before and after a workout. Pre-albumin is a major blood protein that is commonly used as a marker of malnutrition in hospital patients. It is also believed to be an anabolic molecule.

Results showed a significant association between low testosterone and pre-albumin.

Moreover, the association was moderately positive. As a result, low testosterone and pre-albumin are now considered objective biochemical markers for hypotestosteronism. 

As an anabolic hormone, testosterone has a broad range of effects on metabolic regulation.

It's associated with increased lean mass, strength and cardiovascular capacity. Testosterone also increases bone and cartilage growth, and facilitates protein deposition. During puberty, testosterone receptor sensitivity increases.

Research suggests that changes in circulating testosterone influence carbohydrate and fat metabolism.

This means that athletes may be better able to use carbohydrates, but they may also be more susceptible to fats, resulting in a larger adipose mass. However, it's unclear whether testosterone is the culprit.

Other hormones, such as estrogen, can alter the balance of substrates.

Studies have also shown that testosterone may have a positive effect on nutrient storage.

The research shows that testosterone is associated with an increase in red blood cells, which carry more oxygen to muscles.

One study showed that testosterone can enhance aerobic fitness. Another showed that testosterone can augment muscle growth. In this study, a single dose of 10 mg testosterone was administered to men over 65 and had a noticeable effect.

Testosterone stimulates cellular growth by increasing red blood cell (RBC) formation and tissue capillarity.

It also increases blood flow to exercising muscles. The androgen receptor (AR) is responsible for this. Interestingly, the androgen receptor is not directly accessible to most tissues.

But the androgen receptor does interact with other hormones, including estrogen.

While testosterone is important to achieving and maintaining muscle mass and strength, the benefits of it may be minimal in some cases.

To determine its value in enhancing muscular performance, scientists used an experimental protocol to compare two hormone-rich environments. Each group performed a cycle test to measure aerobic fitness.

For the purposes of this study, researchers decided to investigate the relative efficacy of testosterone compared to placebo.

Researchers randomized a control group to receive a placebo and a placebo group to receive a testosterone gel.

They then analyzed their blood samples using a variety of assays, ranging from quantitative enzymatic tests to spectrophotometric measurements.

Although the study is small in sample size, researchers did find that testosterone treatment resulted in a substantial increase in the gas exchange lactate threshold.

This was also accompanied by a notable decrease in age-related decline in peak oxygen uptake.

Conclusion

The androgens are a class of hormones found in males and females. Androgens have many physiological effects, such as the promotion of bone mass and lipoprotein synthesis, maintaining cognitive function, and influencing insulin responsiveness.

In addition to producing testosterone, the male testes also produce estrogen. Estrogen plays a critical role in sustaining female bodily functions. It also may play a role in adaptive exercise responses in women.

There are a number of endocrine systems that control the actions of organs and cells. These include testosterone, estrogen, progesterone, and gonadotropin secretion.

Testosterone has a number of endocrine functions, including reducing body fat, increasing muscle mass, and increasing hemoglobin concentrations.

Several sex hormones have been shown to have positive performance implications for endurance running.

Testosterone is also known to boost musculotendinous stiffness and cardiac output.

Additionally, the anabolic properties of testosterone have been demonstrated. This testosterone-related effect may play a key role in regulating dietary amino acid availability.

Some of the more interesting testosterone related findings are related to androgens' impact on the body's ability to adapt to acute exercise.

Specifically, direct lactate stimulation has been shown to increase plasma testosterone levels. However, the androgen's impact on recovery is less certain.

As well, there is evidence that testosterone is involved in a number of other important processes. For example, it has been shown to promote hepatic-IGF-1 production, which in turn stimulates anabolic signaling pathways.