Static-dynamic (slow, no-relaxation) for endurance?

It builds muscle and strength in untrained people, about as much as or somewhat less than heavy lifting. In 24 untrained young men, 12 weeks of knee extension at about 50% 1RM, 3 s up and 3 s down with no relaxing phase, 3 sets to failure at an 8RM load, grew quadriceps CSA 5.4% against 4.3% at about 80% 1RM (not significantly different, 8 per arm), while the same load and work at normal speed, not to failure, did not; 1RM rose in all three groups with no significant group difference, isometric strength rose more with heavy loads (REF-1171, B+).

A whole-body version (5 exercises, about 55-60% 1RM, twice a week for 13 weeks) raised summed muscle thickness 6.8% and summed 1RM 33.0% against 9.1% and 41.2% with heavy loads — about three-quarters of the heavy gains, no between-group test in the abstract (REF-1172, B+).

The Moscow IBMP trial of training without relaxation at 50% MVC gave +21% strength and +9% muscle volume against +35% and +17% at 80% MVC, not significantly different with 9 per group, on half the work (REF-1169, B); the lab's summary states the heavy gains were larger (REF-1170, C+, abstract).

In adults aged 59-76 the slow style at 50% 1RM raised thigh muscle thickness and knee strength; normal speed at that load raised strength with limited growth (REF-1174, B+, abstract, no heavy group).

Effort, not slowness, is the likely driver (the base's inference). With sets taken to failure, repetitions of 0.5-8 s grew muscle alike, and very slow ones (over 10 s) looked inferior on few studies (REF-1176, A-, abstract); with all else equal, about 3.5-s repetitions grew muscle no better than about 1-s ones (difference 0.09 favouring faster, 95% CrI −0.04 to 0.22; REF-1177, A-, abstract).

Light (≤60% 1RM) and heavy loads gave similar hypertrophy when sets went to failure, while 1RM rose more with heavy loads (REF-677, A).

The light arms that did not grow were ones that, as far as the entries say, stopped short of failure: normal-speed 50% 1RM sets of a fixed 8 or 10 repetitions in REF-1171 and REF-1175 (probably far from failure — the entries' inference) and volume-matched 30% 1RM sets short of failure in REF-1178 (B+, abstract; failure and total volume confounded).

In the LST trials the slow arm differed from its light control in tempo, continuous tension and proximity to failure at once, so tempo was never isolated; failure itself is not required, stopping a little short gave nearly the same growth (REF-678, A-).

Type I fibre growth: a low-level signal, and not specific to the method. The IBMP summary reports that growth in the area occupied by type I fibres predominated after no-relaxation training at 50% 1RM and type II after 80-85% 1RM — no numbers, n or statistics in the abstract, cohorts likely overlapping, size and fibre share not separated (REF-1170, C+).

In 21 young men, 30% 1RM and 80% 1RM both taken to failure each increased type I fibre CSA (REF-1178, B+, abstract, about 7 per arm, tempo not reported).

Across 8 small randomised biopsy trials (195 young adults, six of eight trials untrained or physically active, loads 15.5-92.5% 1RM, seven of eight to failure; tempo stated only for Schuenke 2012, at 1-2 s per phase, whose slow-speed arm was not among the arms analysed — so no slow no-relaxation sets as far as the review reports, the base's reading), type I fibre growth showed no clear change with load (slope −0.005 SMC per 10% 1RM, 95% CI −0.082 to 0.072) while type II growth leaned upward with heavier loads (0.054, −0.038 to 0.145); the type II minus type I contrast ran from −0.147 at 20% 1RM to 0.265 at 90%, every 95% CI including zero (REF-1195, A-, exploratory).

On the point estimates most of that tilt toward type I at light loads came from type II fibres growing less rather than type I fibres growing more, but the type I slope's CI is wide and in the review's aggregated type II model the two slopes were about equal and opposite (−0.017 vs 0.019), so which fibre type drives it is unsettled (inference).

After 6 weeks of 30% 1RM squats to failure, type I CSA did not rise significantly (P = 0.116; REF-1179, B). In young elite cyclists, 16 weeks of added strength training (programme not described in the abstract) shifted fibres from IIX to IIA with no change in fibre area or capillarisation (REF-075, B).

Mitochondria and capillaries: never measured after the method itself; the indirect data are mixed. Light sets to failure at normal tempo (30% 1RM, 1.75 s down and 1.75 s up, about 50-105 s per set by the entry's calculation) raised type I capillary contacts about 18% (4.53 → 5.33) and maximal mitochondrial respiration about 30% in 10 men, with no change in any measured mitochondrial protein; the authors judged resistance exercise insufficient to raise mitochondrial content in 6 weeks, and a thigh cuff on the other leg added no oxidative gain (REF-1179, B, no non-training control). 30% 1RM to failure raised mitochondrial proteins of autophagy, fission and fusion — markers of turnover and remodelling, with no content marker reported (REF-1178, B+, abstract).

One bout of 6-s up / 6-s down repetitions at 30% 1RM to failure raised mitochondrial protein synthesis 114% over 0-6 h, but by 24-30 h a fast bout short of failure had raised it too (REF-1180, C+, n = 8, acute).

LST does deoxygenate the muscle more deeply than heavy or light normal-speed lifting and produces lactate similar to heavy lifting — an acute state, not an adaptation (REF-1171, B+).

Endurance training itself raised mitochondrial content 23-27% across modes (REF-465, A), and capillaries per fibre rise about 10-20% within weeks in untrained people, more slowly in well-trained endurance athletes (REF-466, B+).

Endurance performance: no trial in trained endurance athletes. In 34 soldier-runners (12-22 km a week), 4 weeks of slow bodyweight strength work (7-s repetitions, 84-s sets, 4 sets, 90 s rest, twice a week, no progression) raised knee-extension torque 13.3% (slow dynamic sets) and 14.2% (holds) against 2.5% — significant against controls for the holds only — and jump height 5.4% and 4.1% against 0.7%, while the 3000 m improved −2.8% and −2.6% against −0.8% in controls, not significantly (interaction P = 0.421); the trial was underpowered for the time trial and did not measure running economy (REF-1181, B+).

Thirteen weeks of slow no-relaxation squats at about 60% 1RM made pedalling force and quadriceps EMG less variable in non-cyclists (CV −18% and −21%), heavy squats did not; no power, efficiency or performance was measured, so the direction of the effect for cycling is unknown (REF-1173, B).

In runners, submaximal-load strength work (40-79% 1RM) did not significantly improve economy while heavy work did, and across endurance sports heavy maximal-force training beat lighter intensities (SYNTH-44, citing REF-801 and REF-074, A-; the tempo of those lighter programmes is not stated there).

Fast strength and power: no significant gain in the loaded trials. Slow squats at 50% 1RM for 8 weeks raised squat 1RM 10% and quadriceps thickness 6-10% but did not significantly change lifting power, leg extension power, the rate of EMG rise or jump height (n = 9; REF-1175, B, abstract).

LST raised no isokinetic knee torque at 90-300 deg/s, and its authors advise adding fast exercise (REF-1171, B+). In isometric training, early rapid force rose only with "fast and hard" contractions (REF-1161, B+, untrained men) — intent the slow method does not train.

The one exception is a low-baseline one: in soldier-runners with little strength-training background, 4 weeks of slow bodyweight sets raised countermovement jump 5.4% against 0.7% in controls (P = 0.003; REF-1181, B+) — an early gain in novices, not evidence that slow sets build power in trained athletes (the base's inference).

Lower mechanical stress, not lower metabolic stress. Peak systolic pressure during LST was lower than during heavy lifting (heavy 227.6 ± 24.9 mmHg) at about 60% of the heavy load (REF-1171, B+, acute, untrained young men); creatine kinase rose less and blood lactate more after no-relaxation than after heavy training (REF-1169, B).

The growth-hormone, IGF-1 and cortisol rises after no-relaxation sessions (REF-1169, REF-1170) do not explain the gains: the heavy groups grew at least as much with smaller or no rises, and the metabolite case for hypertrophy is indirect (REF-682, C). The occlusion literature itself lists fast-twitch fibre recruitment among its proposed mechanisms (REF-106, C+).

For an endurance athlete with gym access, heavy lifting stays the strength default (SYNTH-43 B+, SYNTH-44 B+); static-dynamic work is not a substitute for it, because lighter-load strength work did less for economy and performance in endurance athletes (SYNTH-44, citing REF-801 and REF-074) and no static-dynamic trial in trained endurance athletes exists.

When heavy loading is ruled out or unwanted (a joint, a technique or equipment limit, an introductory block, an athlete who will not lift heavy), slow no-relaxation sets are a reasonable way to keep or build muscle — provided each set ends close to failure, which is what the light arms that grew appear to have had in common (REF-1171, REF-1172, REF-677; "close to failure" rather than "slow" as the active ingredient is the base's inference).

Keep something fast in the week — the heavy lifts with fast intent, jumps, or high-cadence riding — because in the loaded trials the slow method did not significantly raise fast strength or power (REF-1175, REF-1171; the jump gain in REF-1181 was in runners new to strength work); the choice of fast element is practice.

Build the engine with endurance training, not in the gym: no entry shows the method adding mitochondria or capillaries (REF-465, REF-466; the indirect light-load data are in Key Finding 4).