Strength and jump performance were mostly kept or improved when HIIT was combined with resistance training, in a narrative systematic review of 18 small controlled trials (14 to 120 participants; older and middle-aged adults, recreationally active adults, team-sport and military samples); with no effect sizes and many trials lacking a resistance-only comparison, it cannot say how large any interference is
Main caveat: The authors' own: small samples, mostly athletic and older cohorts; heterogeneous duration, exercises, sequencing and workload; blinding rarely possible.
Chang and colleagues asked what combining high-intensity interval training with resistance training does to muscle and tendon function in healthy adults: maximal strength, explosive performance, EMG, muscle size and architecture, tendon outcomes, adherence and safety.
They searched four databases to November 2025 and kept 18 controlled trials, from 14 to 120 participants, in older or middle-aged adults (6 trials), recreationally active or trained adults, team-sport athletes and military-aged volunteers.
Most programmes ran 8-12 weeks with 2-3 resistance sessions a week; the intervals were mostly 15-60-s bouts at roughly 90-120% of maximal aerobic power, plus sprint and repeated-sprint formats. Because protocols and outcomes differed so much, the authors did not pool; they described the direction of results by domain.
Maximal strength usually rose or held when resistance loading stayed moderate to high; jump and sprint performance mostly held or improved, especially when the lifting kept a power component; 2-week programmes did not consistently improve strength or jump. EMG and muscle-size data were sparse, no trial imaged a tendon, attendance was mostly 85-95% and adverse events were rare.
The authors conclude that well-designed combinations can maintain or improve musculoskeletal performance and say the absence of consistent interference is not evidence that concurrent and resistance-only training are equivalent.
Participants
18 trials, 14 to 120 participants each; total not reported.
Older and middle-aged adults (6 trials): inactive women about 40-64, older men about 65-80, middle-aged adults with low lean mass, other older adults.
Recreationally active or trained adults: young men in several trials; men and women in two military-aged or recreationally active samples.
Athletes: young competitive soccer players (three trials), amateur rugby sevens players (about 36), water-polo players the review calls elite, professional soccer players (one trial).
Excluded: clinical populations, adolescents, people recovering from injury or surgery (the youth soccer trials were nevertheless included).
Sex split and baseline strength across trials: not reported.
Protocol
Search: PubMed, Web of Science Core Collection, Scopus, PsycINFO (EBSCO), no start date, to 30 November 2025, English, reference lists hand-searched. 1,416 records, 474 duplicates, 942 screened, 75 full texts, 57 excluded, 18 included.
Eligibility: healthy adults; HIIT (sprint-interval and repeated-sprint formats counted) and resistance or power training within one programme, same session or separate days; at least one comparator (resistance-only, HIIT-only, endurance, or another sequencing or configuration); at least one musculoskeletal outcome with pre and post data. Programmes combining resistance training only with steady aerobic work were excluded.
Risk of bias: Cochrane tool for randomised trials, two reviewers by consensus; used to temper confidence, not to exclude.
Synthesis: narrative by domain; no pooled effects, heterogeneity statistics or subgroup analyses (too few comparable trials, by the authors).
Funding and interests: no external funding; no conflicts declared.
Key Results
| Domain | Direction reported (no effect sizes) |
|---|---|
| Maximal strength, older and middle-aged adults | Small to moderate gains over 8-12 weeks in leg press, knee extension and functional strength |
| Maximal strength, recreational adults and athletes | 1RM usually rose when resistance loading stayed moderate to high; 2-week programmes did not consistently raise it |
| Jump and sprint | Mostly held or improved over 4-8 weeks in athletes; not consistently improved in 2-week programmes; better with power-oriented lifting |
| EMG | A handful of trials; lower or unchanged activation at submaximal loads in older adults, preserved or slightly higher in explosive tasks in younger samples |
| Muscle size and architecture | Small gains or maintenance in older adults; larger gains in some younger samples with progressive loading; no significant gain with very brief sprint programmes |
| Tendon | No trial measured tendon stiffness, cross-sectional area or elongation directly |
| Adherence and safety | Attendance mostly 85-95%; no injuries or complications attributed to the programmes in most trials; mild soreness most common |
Risk of bias (Table 1): 16 trials "some concerns" (unclear randomisation or allocation concealment, no blinding, small samples, contamination in team settings); 2 high (a single-group pre-post programme with no control; a non-randomised in-season study). None rated low.
Design features linked by the authors with better strength outcomes (Table 4, narrative): 2-3 progressive resistance sessions a week, 1-3 HIIT sessions, HIIT on separate days or after upper-body work; less favourable: programmes of 2 weeks or less, low resistance volume, frequent lower-body HIIT just before heavy lifting.
Comparators: several trials compared two concurrent formats, concurrent training with usual team practice, or had no resistance-only arm; only some (for example a recreationally trained 8-week trial and a rugby sevens trial) compared directly with lifting alone.
Practical Application
Short HIIT sessions added to a lifting programme usually left strength and jump intact or still improving when the lifting stayed heavy and progressive. This is a direction counted across 18 small trials, most of them not against lifting alone, with no effect size; it does not show that HIIT costs nothing.Where a trial had a strength-only arm, as in 8 weeks of training in recreationally trained young men, 1RM rose in both groups and the strength-only group tended to accumulate more volume load.
The design advice matches the base's. Keep 2-3 progressive resistance sessions, put the intervals on other days or after the lifting, and keep a power element if jump or sprint matters; this is the same scheduling logic as SYNTH-21 (explosive strength is what concurrent training costs, separate by ≥3 h, REF-330). The review's version is narrative, not tested.
Inference, not tested here: an endurance athlete's main load is long aerobic volume, which this review excluded; it says little about interference for a cyclist or runner lifting around a large weekly volume of riding or running.
Tendons: no trial measured them, so the review cannot support claims that tendons keep up with muscle in concurrent training (SYNTH-21 Key Finding 4 stays the base's framing).
Limitations
The authors' own: small samples, mostly athletic and older cohorts; heterogeneous duration, exercises, sequencing and workload; blinding rarely possible; EMG, architecture and tendon outcomes sparse; no long-term follow-up; adherence measured in different ways; narrative synthesis with no pooled estimates; protocol not registered.
Comparators: many trials had no resistance-only arm (usual practice, another concurrent format, or none), so the review mostly shows that concurrent programmes improve or hold strength, not whether HIIT reduced the gain.
Inclusion inconsistencies: a single-group pre-post study with no control (rated high risk) and a single-session crossover of acute signalling are among the 18 controlled training trials; Table 2 calls the single-group study randomised; youth soccer samples were included although adolescents were excluded; one trial's endurance work was moderate to high-intensity cycling or running rather than defined HIIT.
Internal contradictions: Table 3 reports no change to a slight increase in tendon stiffness in older adults while the text states no trial measured tendons; Table 2 describes several trials' comparators only by example or as uncertain ("and/or", "e.g."), which suggests the extraction did not pin the designs down.
Supplementary tables (item-level risk of bias, adherence) were not available to us.
How this entry was checked and changed
Why this level
systematic review of mostly small controlled trials with serious heterogeneity, risk of bias read in full (none low, 16 some concerns, 2 high), so A- at most; its narrative synthesis gives no effect sizes, most comparators are not resistance-only, and its tables contradict each other (see Limitations)