Charles F. Kearns’s research while affiliated with Rutgers, The State University of New Jersey and other places

The dietary supplement ephedra is a potent sympathomimetic that was banned by the US Food and Drug Administration in 2003 because of its deleterious effects on cardiovascular function and thermoregulation during exercise. Unfortunately, extracts of ephedra can still be obtained via the internet and are in use worldwide. The horse is the only athletic species other than humans that sweats to thermoregulate and it controls cardiovascular function in a similar fashion. The purpose of this study was to use the horse to examine the acute effects of ephedra (Ma Huang) to investigate on markers of performance as well as effects on cardiovascular function and thermoregulation during acute exercise. Six Standardbred mares (~450 kg; 6-12 years of age) were used in a crossover design consisting of a ephedra (Ma Huang containing 8% ephedra alkaloid) and control (applesauce) group. All horses performed an incremental graded exercise test (GXT) at a 6% fixed grade to measure oxygen uptake (VO2), run time, velocity at VO2max, maximal velocity, recovery time, haematocrit, total plasma protein concentration, heart rate, right ventricular pressure (RVP), pulmonary arterial pressure (PAP), rectal temperature and recovery. Measurements were recorded at rest, during exercise and post 2 and 5 min recovery. There was a difference (P < 0.05) in pre-exercise haematocrit but not in any other haematocrit or plasma protein sampling intervals. VO2 was greater (P < 0.05) for the ephedra group before exercise, at each step of the GXT, at VO2max, and during recovery compared to the control group. Recovery time was significantly different, but run time was not (P > 0.05). Heart rate was elevated (P < 0.05) at 2 and 5 min recovery in horses administered ephedra. Significant differences were observed for RVP and PAP and rectal temperature during recovery. Recovery score (sweating response, respiration rate, behaviour) was altered (P < 0.05) by ephedra administration. These data suggests an increase in energy expenditure and thermogenesis when horses consume ephedra. However, markers of performance (run time, velocity at VO2max, and maximal velocity completed) were not altered by ephedra administration.

Older horses have an increased risk of hyperthermia due to impaired cardiovascular function. While many studies have investigated thermoregulation in horses during exercise, none have investigated the effects of ageing. To test the hypothesis that there is a difference in thermoregulation during exercise and plasma volume (PV) in young and old horses. Study 1: 6 young (Y, 7.7 ± 0.5 years) and 5 old (O, 26.0 ± 0.8 years) unfit Standardbred mares (507 ± 11 kg, mean ± s.e.) ran on a treadmill (6% grade, velocity calculated to generate a work rate of 1625 watts) until core temperature reached 40 °C. Core (CT), skin (ST), rectal temperature (RT) and heart rate (HR) were measured every min until 10 min post exertion. Packed cell volume (HCT), lactate (LA) and plasma protein (TP) were measured in blood samples collected before, at 40 °C and every 5 min until 10 min post exercise. Sweat loss was estimated using bodyweight. Study 2: Plasma volume was measured in 26 young (8.2 ± 0.7 years) and 8 old (26.6 ± 0.7 years) Standardbred mares (515 ± 12 kg) using Evans Blue dye. Pre-exercise blood (rBV) and red cell (rRCV) volumes were calculated using PV and HCT. Data analysis utilised repeated measures ANOVA and t tests and data are expressed as mean ± s.e. Old horses reached 40 °C faster (998 ± 113 vs. 1925 ± 259 s; P < 0.05) with a greater HR at 40 °C (184 ± 6 vs. 140 ± 5 beats/min; P < 0.05) and greater sweat losses (P < 0.05). Heart rate did not differ (P > 0.05) post exercise. Age did not alter (P > 0.05) CT, ST, RT, LA, HCT or TP. Plasma volume was greater in Y vs. O horses (P < 0.05, 28.5 ± 1.4 vs. 24.1 ± 1.6 l) as was rBV (41.3 ± 2.0 vs. 35.3 ± 2.3 l) and rRCV (13.3 ± 0.6 vs. 11.1 ± 0.8 l). Ageing compromises the ability to handle the combined demand of exercise and thermoregulation in part due to decreased absolute pre-exercise PV.

The purpose of this study was to test the hypotheses that ageing would result in a decline in maximal heart rate (HRmax) and maximal aerobic capacity (V̇O2max) and, secondarily, that those effects would be reversible with training. Eighteen, healthy, unfit Standardbred mares representing 3 age groups: young (Y = mean ± s.e. 6.8 ± 0.4 years, n = 6); middle-aged (MA = 15.2 ± 0.4 years, n = 6); and old (O = 27.0 ± 0.2 years, n = 6) were used. HRmax, V̇O2max and oxygen pulse at V̇O2max (OPmax) and the velocities producing HRmax (V̇HRmax) and V̇O2max (VV̇O2max) were measured during pretraining and post-training incremental exercise tests (GXT). During training, mares exercised 3 days/week (Weeks 1–8) and 4 days/week (Weeks 9–12) at a submaximal intensity (∼60% HRmax) for ∼30 min/day. There were no differences (P>0.05) between Y and MA, before (218 ± 2 vs. 213 ± 3 beats/min; 116 ± 3 vs. 109 ± 3 ml/kg bwt/min; 0.55 ± 0.01 vs. 0.52 ± 0.02 ml/kg/beat; 9.0 ± 0.3 vs. 9.3 ± 0.2 m/s; 8.8 ± 0.2 vs. 8.8 ± 0.2 m/s) or after training (224 ± 2 vs. 218 ± 2 beats/min; 131 ± 3 vs. 120 ± 2 ml/kg bwt/min; 0.58 ± 0.01 vs. 0.55 ± 0.01 ml/kg/beat; 10.5 ± 0.2 vs. 9.5 ± 0.1 m/s; 10.6 ± 0.2 vs. 9.5 ± 0.1 m/s) for HRmax, V̇O2max, OPmax, V̇HRmax or VV̇O2max, respectively. Old horses had lower HRmax, V̇O2max and OPmax and reached them at lower velocities compared to Y and MA (P<0.05), both before (193 ± 3 beats/min; 83.2 ± 2.0 ml/kg bwt/min; 0.43 ± 0.01 ml/kg/beat; 7.8 ± 0.1 m/s; 7.2 ± 0.1 m/s) and after training (198 ± 2 beats/min; 95 ± 2 ml/kg bwt/min; 0.48 ± 0.01 ml/kg/beat; 8.2 ± 0.2 m/s; 8.0 ± 0.2 m/s). Training did not alter HRmax in any age group (P>0.05) but did cause increases in V̇O2max, OPmax and VV̇O2max for all groups (P<0.05). Interestingly, training increased VHRmax only in Y (P<0.05). These data demonstrate that there is a reduction in HRmax, V̇O2max, OPmax, VHRmax and VV̇O2max in old horses, and that training can partially reverse some effects of ageing.

Reasons for performing study: Ageing appears to affect immune and neuroendocirne function in horses and response to acute exercise. No studies have examined the combined effects of training and ageing on immune and neuroendocirne function in horses. Hypothesis: To ascertain whether training and age would affect the plasma β‐endorphin (BE) and cortisol (C) as well as immune function responses to acute exercise in Standardbred mares. Methods: Graded exercise tests (GXT) and simulated race tests (SRT) were performed before and after 12 weeks training at 60% HR max . BE and C were measured at rest and at 5, 10, 20, 40, 60 and 120 min post GXT. Leucocyte cell number, CD4 ⁺ and CD8 ⁺ lymphocyte subsets, and mitogen stimulated lymphoproliferative response (LPR), were measured in jugular blood before and after the SRTs. Results: Cortisol rose by 5 min post GXT in young (Y) and middle‐age (MA) mares (P<0.05) and remained elevated until 40 and 60 min post GXT, respectively during both pre‐ and post training GXT. There was no rise in C in old (O) mares after either GXT (P>0.05). Pretraining BE rose (P<0.05) by 5 min post GXT in all mares. After training, BE was higher in Y and O vs. MA (P<0.05) at 5 min post GXT. Post training BE was higher at 5 min post GXT in Y and O vs. pretraining (P<0.05). After SRT, lymphocyte number rose in all mares (P<0.05); however, lower lymphocyte numbers (P<0.05) were seen in MA vs. Y and O vs. MA (P<0.05). The O had reduced LPR to Con A and PHA stimulation (P<0.05) compared to Y and MA after the SRT after both pre‐ and post training SRT. LPR to PWM was lower (P<0.05) in O vs. Y and MA after the pretraining SRT. Training caused an increase in resting LPR to PWM in MA only (P<0.05). Conclusion: Both age and training altered the plasma β‐endorphin and cortisol responses as well as and immune responses to acute exercise. Potential relevance: This study provides important information on the effects of ageing and training that will aid in the management and care of an increasing number of active older horses.

The purpose of this study was to investigate once-daily walk training with restricted leg blood flow (KAATSU) on thigh muscle size and strength. Twelve young men performed walk training: KAATSU-walk training (n=6) and control (no KAATSU-walk; n=6). Training was conducted once daily, 6 days per week, for 3 weeks. Treadmill walking (50 m/min) was performed for 5 sets of 2-min bouts interspersed with 1-min rest periods. The KAATSU-walk group wore pressure cuff belts (5 cm wide) on both legs during training, with incremental increases in external compression starting at 160 mmHg and ending at 230 mmHg. Thigh muscle volume and isometric and 1-repetition maximal (1-RM) strength were measured before and after training. In the KAATSU-walk group, quadriceps and hamstrings muscle volume increased 1.7 and 2.4% (both P<0.05), respectively, following training. One-RM leg press and leg curl increased 7.3 and 8.6% (both P<0.05), respectively, following KAATSU-walk training. Also, isometric knee extension strength (4.4%; P<0.01), but not knee flexion strength (1.7%), increased following KAATSU-walk training. There were no changes in muscle volume or strength in the control-walk group. These results confirm previous work showing that the combination of slow walk training and leg muscle blood flow restriction induces muscle hypertrophy and strength gains. However, the magnitude of change in muscle mass and strength following once-daily KAATSU-walk training was approximately one-half that reported for twice-daily KAATSU-walk training over a 3-week period. These results in combination with previous observations lead to the conclusion that the impact of KAATSU-walk training on muscle size and strength is related to an ability to accomplish a high number of training bouts within a compressed training duration. Second, frequency-dependent muscle enlargement appears to be associated with KAATSU-walk training.

Clenbuterol is a beta(2)-agonist and potent selective bronchodilator that is used to treat bronchospasm in the horse. The drug is normally administered to horses orally as a syrup formulation. Once absorbed into the systemic circulation, clenbuterol has the potential to cause many side effects, including a repartitioning effect and major alterations in cardiac and skeletal muscle function. Recent studies have also reported that clenbuterol can affect bone and the immune, endocrine and reproductive systems. A great deal of information has been published on the beneficial effects of short term therapeutic doses of clenbuterol on the equine respiratory system, although there is limited information about chronic administration, particularly since this has been associated with adverse physiological effects on other systems. This review summarizes the relevant understanding of clenbuterol for clinicians and horse owners who may administer this drug to pleasure and performance horses.