**3. Results**

#### *3.1. Sprint Speed*

Sprint speed was not a ffected by protocol for the distances 0–5 m (F(2,26) = 0.34, *p* > 0.05, η2 = 0.03), 5–10 m (F(2,26) = 0.27, *p* > 0.05, η2 = 0.04), 0–10 m (F(2,26) = 0.46, *p* > 0.05, η2 = 0.10) and 0–20 m (F(2,26) = 0.79, *p* > 0.05, η2 = 0.06) (Table 2). However, a statistically significant e ffect of protocol on sprint speed was detected for the 10-20m distance (F(2,26) = 5.85, *p* = 0.008, η2 = 0.31). More specifically, post-hoc tests revealed significantly higher sprint speed over the 10-20m distance after the BwR protocol compared to control (*p* = 0.019, CI95%: 0.025 to 0.30).

The percent change in sprint speed after the BwR and FwR relative to the CON protocol was highly variable among subjects for the distances 0–5 m, 5–10 m and 0–10 m, revealing participants with either lower or higher performance than the CON protocol (Figure 1). More systematic trends were observed for 10–20 m and 0–20 m distances. More specifically, for the distance 10–20 m the speed after the BwR protocol was 2.4 ± 2.9% higher than the CON and it was statistically di fferent from zero (CI95%: 0.8 to 4.1% *p* = 0.008) while the increase by 1.6 ± 2.9% for the FwR compared to the CON was not significantly di fferent from zero (CI95%: −0.1 to 3.3%, *p* = 0.065). Regarding the 0–20 m distance speed after the BwR was 0.9 ± 2.6% higher than the CON and 0.0 ± 2.4% after the FwR protocol. Both percentages were not significant from zero (BwR CI95%: −0.6 to 2.4 *p* = 0.241, and FwR CI95%: −1.4 to 1.4 *p* = 0.972, respectively).

**Table 2.** Mean and standard deviation (SD) values of sprint speed (m/s) for the 20 m sprint and its intermittent distances for the warm-up protocols (CON: typical warm–up; BwR: typical warm–up plus 3 × 10 m backward running bouts; FwR: typical warm–up plus 3 × 10 m forward running bouts). Significantly higher values compared to the CON protocol are designated with asterisks (\*: *p* < 0.01).


**Figure 1.** Percent change in 20 m sprint speed and its intermittent distances after the BwR and FwR protocols relative to the control protocol. Gray area corresponds to the CI95% and vertical lines to the SD of mean, shown as a horizontal line in the middle of the gray area.

#### *3.2. Rate of Perceived Exertion*

A statistically significant effect of protocol was found on RPE (F(2,26) = 24.2, *p* < 0.001). Post-hoc tests revealed a statistically significantly lower RPE in the CON protocol (1.9 ± 0.8, *p* < 0.001) compared to the BwR (4.1 ± 1.5) and FwR (4.2 ± 1.2) warm-up protocols. This indicates that implementing either 3 × 10 m BwR or FwR after a typical warm-up causes a similar RPE, which is higher relative to the typical warm-up per se.
