Regular exercise may help slow the early blood sugar changes that often appear years before diabetes is diagnosed.
A review of clinical trials suggests that combining aerobic and strength training can improve glucose control in sedentary adults, even before medication becomes necessary.
Changing blood sugar without meds
New World Health Organization data put adult inactivity at 31% worldwide, and prevention keeps losing ground.
Researchers at the University of Coimbra (UC) pull together evidence on workouts that can change blood markers in sedentary adults.
The work was led by Fernanda M. Silva, a sport science researcher at UC, and her focus stays on metabolism.
That focus matters because early changes in glucose handling can show up years before diabetes, when habits still feel flexible.
What combined training means
Combined training pairs steady aerobic movement with resistance work, so the heart and muscles train in the same week.
During aerobic sessions, working muscles pull more glucose from blood, because contractions open transport channels without needing much insulin.
Resistance sets add muscle fibers and increase storage space for sugar, which can ease the day-to-day load on insulin.
When people keep both pieces in their routine, the body gets two separate nudges that often stack together.
How the evidence was gathered
Instead of leaning on one small trial, UC researchers reviewed controlled experiments that compared combined training against doing nothing new.
Their 2024 meta-analysis, a method that combines results across many trials, pools 24 controlled studies and follows 852 sedentary adults.
Each randomized controlled trial, participants assigned by chance to exercise or control, helped separate training effects from normal drift.
Even with that design, differences in workout intensity and testing schedules mean the summary cannot name one perfect routine.
Blood markers that signal trouble
Clinicians track fasting glucose and insulin because those numbers reflect what the body does between meals and overnight.
In prediabetes, insulin resistance, when cells respond poorly to insulin, often rises first and pushes insulin higher.
Researchers often summarize this strain with HOMA-IR, a calculation from fasting glucose and insulin, to estimate whole-body insulin sensitivity.
Longer-term exposure shows up in HbA1c, a 3-month average of blood sugar, which can stay normal despite brief swings.
Where the biggest moves appear
Overall, people who followed combined training showed lower fasting blood sugar and needed less insulin than those who stayed inactive.
Their bodies also handled insulin more efficiently after training, pointing to better metabolic control.
“Findings from this systematic review and meta-analysis suggest that combined exercise training improves some glucose metabolism markers and inflammatory parameters in sedentary adults without diabetes,” wrote Silva, lead author of the analysis.
Not every blood signal budged, and several longer-term or hormone-related measures stayed much the same across studies.
Inflammation sits in the background of many metabolic problems, because immune cells can interfere with how muscles respond to insulin.
The review sees declines in TNF-alpha, an immune signal that can block insulin action, dropping to -0.972 after combined training.
It also reports lower C-reactive protein, a liver-made marker that rises with inflammation, with a pooled change of -0.507.
Those markers suggest a calmer immune state, yet the evidence cannot show exactly which training details drive the drop.
Why HbA1c can resist change
The review does not find a clear HbA1c change, even when fasting glucose and insulin improve after combined training.
The American Diabetes Association test ties HbA1c to sugar stuck on hemoglobin, so short programs can miss the window.
Most sedentary adults without diabetes start near normal, and only three trials in the review even measured HbA1c.
That gap leaves room for larger studies that run longer and start earlier, before people drift into prediabetes.
What programs looked like
Across the trials, programs last from 8 to 24 weeks, often meeting 3 days each week for about 60 minutes.
Aerobic blocks use walking, cycling, or running, then resistance uses weights or body-weight moves, sometimes in one session.
Federal guidelines recommend 150 minutes of moderate aerobic activity weekly and strength work at least 2 days.
Those targets match many study protocols, but real life often demands shorter bouts that people can repeat without injury.
Exercise and blood sugar
Many included trials are small, and their results vary, which makes any single estimate less firm than it looks.
The paper flags moderate variation across trials and hints of missing negative studies for fasting measures, so the real effect could be smaller.
The timing of blood tests varies, and some inflammation markers rise briefly after exercise before returning to normal.
Until study methods become more consistent, the results point to combined training as a reliable option, not a finely tuned solution for insulin resistance.
Taken together, the evidence says that mixing aerobic and resistance training can improve fasting glucose control in sedentary adults.
It also points to possible inflammation benefits, yet future trials must clarify which people respond best and why TNF-alpha falls.
The study is published in Scientific Reports.
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