REF-1295 · Skovgaard et al., 2017 · Journal of Applied Physiology · Paper · PubMed

Do speed-endurance sessions every second day beat every fourth?

In 18 trained runners, 20 sessions every 2nd or 4th day gave no further 10-km gain after 10 familiarisation sessions; exhaustion time rose in both. B-, abstract.

Main caveat: Abstract only. The SET format, allocation, number of weeks per arm, background training, statistics for between-group comparisons and individual data are not…
limited, mixed evidenceMeasured on trained athletes

Skovgaard, Almquist and Bangsbo asked whether trained runners who already use speed-endurance training (SET) gain more by doing it more often.

After a familiarisation period (FAM) of 10 SET sessions, 18 runners (14 men, 4 women; VO2max 57.3 ± 3.4) completed 20 more sessions either every fourth day (low frequency, LF, n = 7; 2 per 8 days) or every second day (high frequency, HF, n = 11; 4 per 8 days).

During FAM, 10-km performance improved by about 3.5%, time to exhaustion at 90% of vVO2max lengthened 15% (HF) and 22% (LF), running economy improved, VO2max did not change, and muscle NHE1, citrate synthase and phosphofructokinase rose.

During the intervention period (INT), 10-km performance did not change further in either group, while time to exhaustion lengthened a further 12% (HF) and 16% (LF); VO2max, economy and the two enzymes did not change; NKAβ1 rose in both groups, FXYD1 and SERCA1 expression and FXYD1 activity rose in HF, and SERCA2 fell in LF.

The authors conclude that increased or maintained SET frequency improves short-term exercise capacity but not 10-km performance. Our reading: with REF-005 and REF-1293, one more trial in trained athletes where doing quality sessions more often did not improve the endurance outcome; the abstract gives too little to weigh it further.

Protocol

Design (from the abstract): familiarisation (FAM, 10 SET sessions per the abstract's summary statement), then an intervention period (INT) of 20 SET sessions at low frequency (every fourth day) or high frequency (every second day); tests and a vastus lateralis biopsy before FAM and before and after INT. Allocation method and blinding not stated.
Participants: n = 18 runners accustomed to SET (14 men, 4 women); VO2max 57.3 ± 3.4 (units printed "ml/min"); HF n = 11, LF n = 7.
Session: "speed endurance training"; its format (rep length, number, recovery) is not given in the abstract.
Tests: 10-km run; time to exhaustion at 90% of vVO2max; running economy; VO2max; muscle protein expression (NHE1, NKAβ1, FXYD1, SERCA1, SERCA2) and maximal activity of citrate synthase and phosphofructokinase.
Analysis: not described in the abstract beyond P < 0.05.
Funding and interests: not stated in the abstract; PubMed lists the first author's affiliations as the University of Copenhagen and Team Danmark (Danish Elite Sports Organization).

Key Results

OutcomeFAM (10 sessions, all runners)INT, every 2nd day (HF, n = 11)INT, every 4th day (LF, n = 7)
10-km performanceimproved ~3.5% (P < 0.05)no further changeno further change
Time to exhaustion at 90% vVO2max+15% (HF) and +22% (LF) (P < 0.05)further +12% (P < 0.05)further +16% (P < 0.05)
Running economyimproved (P < 0.05)unchangedunchanged
VO2maxunchangedunchangedunchanged
Citrate synthase, PFK maximal activityincreasedunchangedunchanged
Muscle proteinsNHE1 upNKAβ1 up; FXYD1, SERCA1 expression and FXYD1 activity upNKAβ1 up; SERCA2 down
Between groups: the abstract reports no between-group comparison for any outcome; both frequencies produced the same pattern for 10 km (no change) and time to exhaustion (a further rise).
Individual response: not reported in the abstract.

Mechanisms

Measured: after familiarisation, further SET sessions changed ion-transport proteins (Na+/K+ pump subunit NKAβ1 in both arms; FXYD1 and SERCA1 in the high-frequency arm) without changing oxidative enzymes, VO2max or economy.
Authors' interpretation: the better short-term exercise capacity "may be associated with" higher expression of muscle proteins for Na+/K+ transport and Ca2+ reuptake, which matter for fatigue in intense exercise.
Inference: the outcome that improved (time to exhaustion at 90% vVO2max, a few minutes) is closer to what SET trains than a 10-km race is; the 10-km gain came early, in the first 10 sessions, and then plateaued at either frequency.

Practical Application

Do speed-endurance sessions every second day beat every fourth? In 18 trained runners, 20 sessions every 2nd or 4th day gave no further 10-km gain after 10 familiarisation sessions; exhaustion time rose in both. B-, abstract.
More frequent quality sessions were not better for the endurance outcome in trained runners (B-): together with REF-005 (B; three vVO2max sessions a week added nothing over one) and REF-1293 (B-; four short threshold sessions no better than two long ones), this is consistent with SYNTH-26's "Never add hard sessions to compensate for missing hours", though Skovgaard and REF-1293 held total sessions or weekly dose fixed and so did not test adding sessions, and REF-1293 is skiers, not runners.
Expect the early gain and then a plateau (B-, inference from the timeline): about 3.5% on 10 km came in the first 10 sessions; a further 20 sessions held it. Not from this paper; the base's own practice: in the last ~8 weeks "short above-VO2max speed-endurance reps are an option" (SYNTH-47); outside burst-decided racing SYNTH-46 keeps such work "a small standing dose, not a block".

Limitations

Abstract only. The SET format, allocation, number of weeks per arm, background training, statistics for between-group comparisons and individual data are not available here; the full text is not open access.
Small, unequal groups. 11 vs 7, with 4 women among 18.
Matched on sessions, not time. Twenty sessions every second vs every fourth day implies roughly 40 vs 80 days (our arithmetic from the schedule; the abstract gives no durations), so frequency and block length are confounded.
Reporting. VO2max is printed "57.3 ± 3.4 ml/min", which cannot be right for adult runners; presumably mL/kg/min.
Funding and interests: not available from the abstract; the first author is listed with Team Danmark (the Danish elite sports organisation).
How this entry was checked and changed
Why this level

n = 18 trained runners in groups of 11 and 7, read from the abstract only (full text not open). A small two-group study (B); held at B- as an abstract-only small study with key methods missing — the session format, allocation, the length of each arm and the between-group statistics are not in the abstract