Training is all about finding the balance between progress and recovery. Push too hard and the body breaks down, but take it too easy and nothing changes. Athletes and gym-goers are constantly chasing the sweet spot where adaptation happens without creating unnecessary damage. A recent study has taken a close look at this balance, examining how different types of exercise impact hormones, muscle damage, inflammation and oxidative stress. The findings shed light on the best way to train for maximum benefit with minimal downside. For coaches designing programmes and anyone studying pt courses, this research is especially relevant.
The study, published in Sports in June 2025, tested three popular training methods including high-intensity interval training (HIIT), concurrent training (CT) and high-intensity resistance circuit training (HRC) (Martínez-Noguera et al., 2025). Each training method is well known and commonly used. HIIT for example, is well known for improving VO₂max and fat loss. Concurrent training blends strength and endurance in the same session. Circuit-based resistance work has long been used in performance sport as a way to build both strength and conditioning. What the researchers wanted to know was how these different protocols affect the body’s internal environment, not just immediately after the workout but up to 48 hours later. For anyone progressing through a personal trainer course, these insights are valuable for understanding how to build programmes that drive adaptation while protecting recovery.
The Study in Detail
Thirty-three recreationally active young men were recruited. They trained regularly, had healthy body mass indexes, and decent VO₂max scores. Each participant performed all three training protocols in a crossover design, separated by five days of rest to avoid carryover effects. The protocols were carefully controlled:
- HIIT involved short sprints with brief rest periods.
- HRC consisted of heavy resistance exercises performed in circuit fashion, using loads at six-repetition maximum with 40–45 seconds rest between stations.
- CT combined a block of heavy resistance work with a 20-minute treadmill run at ventilatory threshold.
Blood samples were taken at baseline, immediately post-exercise, after 30 minutes, after 24 hours and after 48 hours. The researchers measured hormones like testosterone, cortisol and growth hormone, along with biomarkers of inflammation (IL-6 and TNF-α), muscle damage (creatine kinase and myostatin) and oxidative stress (TBARS and protein carbonyls).
What the Researchers Found
The results told an interesting story. High-intensity resistance circuit training stood out as the most favourable option for promoting recovery and adaptation. Testosterone levels rose higher in HRC than HIIT at 30 minutes and again at 48 hours. This was important because testosterone drives protein synthesis, muscle repair and strength gains. Alongside this, myostatin levels dropped more in HRC than CT, which is notable because myostatin limits muscle growth by inhibiting satellite cell activity. In simple terms, HRC created an anabolic environment that supported muscle building and repair.
All three protocols increased creatine kinase, a marker of muscle damage, but HRC did not produce more damage than the others. Inflammatory responses followed a similar pattern. IL-6 spiked across all exercise types immediately post-exercise, but levels returned to baseline within an hour. TNF-α, another inflammatory cytokine, rose only in the concurrent training condition. This suggests that HRC, despite being high in intensity, does not overload the inflammatory system any more than the alternatives.
Oxidative stress markers added another layer to the picture. HIIT caused a sharp increase in protein carbonyls, a sign of acute oxidative damage, while HRC and CT did not. TBARS, which reflect lipid peroxidation, did rise in HRC, but this elevation was considered manageable and part of the hormetic effect where small amounts of oxidative stress stimulate adaptation. Overall, the findings pointed to HRC as the protocol that provided hormonal benefits without disproportionate damage or inflammation.
Why These Responses Matter
Hormonal, inflammatory and oxidative markers might sound abstract, but they directly influence how training translates into results.
- Testosterone encourages muscle protein synthesis and recovery, while myostatin acts like a brake on growth.
- Cortisol mobilises energy but can promote muscle breakdown if chronically elevated.
- IL-6 is both an inflammatory marker and a signalling molecule that recruits satellite cells for repair.
- Oxidative stress can help trigger adaptations at low levels but causes tissue damage if excessive.
When these systems tilt too far toward stress, recovery slows and injury risk climbs. When they line up in balance, the body adapts quickly and training becomes more effective. The standout finding of the study was that HRC created this balance. It delivered an anabolic punch without tipping the body into prolonged catabolism or systemic stress.
The Case for HRC
Other research supports the benefits of high-resistance circuit training. Alcaraz and colleagues (2008, 2011) showed that circuit-based resistance training improved both strength and aerobic capacity while being time-efficient. It delivered cardiovascular responses similar to traditional aerobic exercise while still building maximal strength. Kraemer and Ratamess (2005) highlighted that short rest intervals and higher workloads tend to drive greater hormonal responses, particularly testosterone and growth hormone. HRC fits this profile neatly, combining high loads with short rest to maximise metabolic and hormonal stimulation.
HIIT, in contrast, is excellent for cardiovascular fitness and metabolic health but carries higher oxidative stress. Concurrent training can be useful for mixed goals, but it often interferes with strength and hypertrophy due to competing adaptations (Leveritt et al., 1999). HRC appears to bridge the gap, providing strength, conditioning and hormonal benefits in a single package.
A Practical HRC Programme
Based on the study’s design and what we know from the wider literature, here is a practical HRC session that captures the essence of the protocol:
Warm-up (10 min):
- Dynamic mobility (hips, shoulders, thoracic spine)
- Bodyweight squats, push-ups, light band pull-aparts
- 5 min of light cardio (rower or bike)
Circuit A (Push–Pull–Leg)
- Back Squat – 6 reps @ 6RM
- Pull-Up or Weighted Lat Pulldown – 6 reps @ 6RM
- Barbell Bench Press – 6 reps @ 6RM
Rest: 40–45 seconds between exercises.
Repeat circuit 3 times.
Circuit B (Hip–Core–Shoulder)
- Romanian Deadlift – 6 reps @ 6RM
- Standing Overhead Press (Barbell or Dumbbell) – 6 reps @ 6RM
- Hanging Knee Raise or Weighted Cable Crunch – 12–15 reps
Rest: 40–45 seconds between exercises.
Repeat circuit 3 times.
Circuit C (Accessory / Finisher)
- Walking Lunges – 12 steps each leg (heavy dumbbells)
- Barbell Row – 6 reps @ 6RM
- Dips or Weighted Dips – 6 reps
Rest: 40–45 seconds between exercises.
Repeat circuit 2 times.
Session Notes:
- Tempo: explosive concentric, controlled 3-second eccentric.
- Rest Between Circuits: 4–5 minutes.
- Duration: ~45–55 minutes.
- Frequency: 2–3x per week, with at least 48 hours recovery.
- Progression: increase load when you can hit 7 reps with solid form, or reduce rest slightly.
This programme balances volume and intensity to stimulate hormones, challenge the cardiovascular system and keep oxidative stress within an adaptive range. Over time, progression can come from increasing load, adding sets or slightly reducing rest.
Download this programme to share with your clients.
And Finally…
The pursuit of gains often comes with the cost of stress and fatigue, but it does not have to be that way. This research highlights high-intensity resistance circuit training as a method that maximises anabolic signals while keeping damage and inflammation in check. It creates an internal environment that supports recovery and growth, making it a smart choice for athletes, coaches and anyone serious about long-term progress. For us as personal trainers, this is a reminder that programming decisions shape not just performance but also the recovery landscape.
Reference
- Martínez-Noguera, F.J., Chung, L.H., Guadalupe-Grau, A., Montoro-García, S., & Alcaraz, P.E. (2025). Comparison of Hormonal, Inflammatory, Muscle Damage and Oxidative Stress Biomarkers Changes in Response to High-Intensity Interval, Circuit and Concurrent Exercise Bouts. Sports, 13(184). Click here to review the full research article.
- Alcaraz, P.E., Sánchez-Lorente, J., & Blazevich, A.J. (2008). Physical performance and cardiovascular responses to heavy resistance circuit training versus traditional strength training. J Strength Cond Res, 22(3), 667–671. Click here to review the full research article.
- Alcaraz, P.E., Perez-Gomez, J., Chavarrias, M., & Blazevich, A.J. (2011). Similarity in adaptations to high-resistance circuit vs. traditional strength training in resistance-trained men. J Strength Cond Res, 25(9), 2519–2527. Click here to review the full research article.
- Kraemer, W.J., & Ratamess, N.A. (2005). Hormonal responses and adaptations to resistance exercise and training. Sports Med, 35(4), 339–361. Click here to review the full research article.
- Leveritt, M., Abernethy, P.J., Barry, B.K., & Logan, P.A. (1999). Concurrent strength and endurance training. Sports Med, 28(6), 413–427. Click here to review the full research article.
Learn How Smart Design Drives Real Adaptation
Recent research published in Sports (Martínez-Noguera et al., 2025) showed that high-intensity resistance circuit training raised testosterone significantly higher than HIIT at both 30 minutes and 48 hours after training, while also lowering myostatin, the protein that blocks muscle growth. In other words, the right training design doesn’t just work muscles, it shapes the internal environment that drives adaptation. On our Gym Instructor & Personal Trainer Practitioner, Specialist and Master Diplomas, you’ll learn how to apply this science in practice, designing programmes that maximise gains while minimising unnecessary stress on the body. With the latest knowledge from hormonal responses to exercise through to practical circuit design, these PT qualifications prepare you to coach clients with confidence and credibility.
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