Do Sprinters and Jumpers Differ in the Acute Countermovement-Jump Response to Isometric Conditioning Protocols? An Exploratory Study

Sprinters and jumpers differ in their force–velocity demands, so this exploratory study compared their acute countermovement jump (CMJ) response to isometric conditioning. Methods: Twenty-two competitive track and field athletes (10 sprinters, 12 jumpers; 19.1 ± 3.3 y) were alternately allocated from a randomised list to a 3 × 5 s isometric knee-extension or isometric half-squat (n = 11 each). Discipline was not manipulated, and no control condition was included. CMJ height was assessed from flight time by frame-by-frame video analysis, with take-off and landing timestamps read to the nearest 0.01 s. The best of three jumps was the primary trial summary. Percentage change (ΔCMJ) was the primary outcome. Results: Sprinters increased (+2.40 ± 4.46%) whereas jumpers decreased (−2.02 ± 6.44%). Discipline and protocol were analysed jointly in one additive model. The protocol contrast was small and imprecise (−0.25 percentage points [ISO-SQ relative to IKE], 95% CI −5.50 to 5.00; p = 0.921). The unadjusted discipline difference was non-significant (4.42 percentage points, 95% CI −0.46 to 9.30; p = 0.074) and the parallel Mann–Whitney U test was borderline and implementation-dependent (p = 0.043–0.050). After age adjustment it attenuated to +2.51 percentage points (95% CI −2.65 to 7.66; p = 0.320), whereas age remained associated with ΔCMJ (−0.86% per year; p = 0.042). Post hoc averaged trial summaries gave larger contrasts. Conclusions: The primary comparison was inconclusive and materially attenuated by age adjustment but directionally consistent across trial summaries and protocols. The observed discipline-dependent pattern is hypothesis-generating and requires confirmation in adequately powered, controlled trials.