Clenbuterol diminishes aerobic performance in horses.

The research article investigates the impact of a drug called clenbuterol on the aerobic performance of horses. The study showed that therapeutic levels of clenbuterol, when combined with training, led to a decrease in aerobic performance in horses.

Methodology

The study involved 23 Standardbred mares divided into four experimental groups:

• Clenbuterol and exercise (CLENEX)
• Clenbuterol only (CLEN)
• Exercise only (EX)
• Control (CON)

The CLENEX group was treated with clenbuterol and exercised for 20 minutes at 50% O2max. The horses were subjected to an incremental exercise test (GXT) to measure maximum oxygen consumption (O2max), blood lactate concentration, total plasma protein concentration, and hematocrit. Additional parameters, including plasma volume, heart rate, right ventricular pressure (RVP), and pulmonary artery pressure (PAP), were measured pre- and post-treatment.

Each horse also performed an exercise capacity test (ECT), where they ran at their pre-treatment O2max speed until exhaustion.

Findings

The study found no significant changes in blood lactate, total protein, or hematocrit among any group during the GXT or ECT. However, the combination of clenbuterol and exercise (CLENEX) led to a decrease in O2max and velocity to O2max. Furthermore, both CLENEX and CLEN groups showed a reduction in time to exhaustion.

Interestingly, exercise alone (EX) led to improvements in O2max, velocity to O2max, velocity to produce lactate concentration, and time to exhaustion. The study also found alterations in plasma volume in the CLENEX and EX groups, with a decrease observed in the CLENEX group and increase in the EX group.

Post-test recovery heart rates were higher in the CLENEX, CLEN, and CON groups compared to their pretest values. Right ventricular pressure remained elevated in the CLEN and CON groups during recovery.

Conclusions

The results suggested that the combination of therapeutic levels of clenbuterol and exercise training reduces aerobic performance in horses. The reduction in plasma volume observed might affect improvements in cardiovascular function typically seen with exercise training. Hence, the use of clenbuterol in training horses may have negative effects on their performance.