Rethinking The Role of A- and B-Skips in Improving Sprinting Performance
Go to any track on any given day and the chances are you’re going to see athletes doing A-skips and B-skips at some point. But how well do these drills actually replicate the movements of maximal sprinting? This article will look into the results of an article examining the kinematic and spatiotemporal differences between sprinting and these popular drills, providing valuable insights for coaches aiming to maximise sprint performance.
What Are A- and B-Skips?
A-skip: Focuses on high knee lift, dorsiflexion of the foot (toes up), and a rapid downward strike of the foot.
B-skip: Similar to the A-skip but adds an exaggerated "pawing" motion where the foot cycles down and extends slightly in front before striking beneath the hip.
These drills aim to reinforce key aspects of sprinting form, such as proper knee drive, foot positioning, and rhythm. However, their effectiveness as true sprint-specific training tools has been questioned.
Key Findings from the Study
1. Hip Flexion Velocity: Faster in Sprinting
One of the standout differences is how fast the leg swings forward at the hip:
Sprinting: 754.9°/second
A-skips: 487.1°/second
B-skips: 463.7°/second
This means that during sprinting, the leg moves forward significantly faster than in either drill. The slower velocities in the drills suggest they may not fully replicate the rapid forward leg motion needed for maximal sprinting.
2. Knee Angles: Differences in Flexion and Extension
The study also measured the angles at which the knee bends and straightens during each movement.
Peak Knee Flexion (when the leg is most bent):
Sprinting: 107.3°
A-skips: 98.4°
B-skips: 102.1°
The knee bends more during sprinting, indicating a more dynamic leg recovery compared to the drills.
Peak Knee Extension (minimum bend at push-off):
Sprinting: 3.3° (slightly bent)
A-skips: -5.5° (hyperextended)
B-skips: -7.6° (hyperextended)
This shows that in the drills, the leg straightens more than it does in sprinting, which could alter force application during push-off.
3. Ankle Kinematics: The Importance of Push-Off Power
Plantar Flexion Angular Velocity (speed of toes pointing down during push-off):
Sprinting: -1326.8°/second (much faster)
A-skips: -642.1°/second
B-skips: -707.9°/second
The rapid downward movement of the foot during push-off is a critical part of generating sprinting power. In both drills, the speed of this movement is much slower than in sprinting, potentially limiting the drills' ability to replicate the explosive push-off required for high-speed running.
Dorsiflexion (toes pointing up):
Sprinting: 12.7°
A-skips: 18.8°
B-skips: 19.9°
The higher dorsiflexion in the drills suggests that the drills may place the foot in a position that differs from the midfoot strike typically seen during sprinting.
4. Step Rate: Sprinting Is Significantly Faster
Step rate measures how many steps an athlete takes per minute.
Sprinting: 253.9 steps/min
A-skips: 94.8 steps/min
B-skips: 92.1 steps/min
The difference is striking: athletes take far fewer steps during the drills than during sprinting. This slower rate is likely due to the additional aerial phase and exaggerated movement pattern in the skips.
Key Takeaway Messages
1. Use A- and B-Skips as Dynamic Warm-Ups, Not Sprint Replacements
The study suggests that A- and B-skips may be better suited as part of a dynamic warm-up rather than as sprint-specific training tools. These drills can help activate key muscle groups and prepare athletes for the demands of sprinting but may not directly improve sprint mechanics.
2. Reinforce Key Movement Patterns with Cues
To get the most out of these drills, coaches should emphasise specific cues:
For A-skips: "Knee up, toes up, punch down."
For B-skips: "Paw down under the hips, not in front." These cues help athletes focus on foot placement and timing, which are crucial for efficient sprinting.
3. Complement with Resisted Sprinting
For drills that more closely mimic sprinting mechanics, consider incorporating resisted sprinting, such as sled pulls or banded sprints. These exercises exaggerate sprinting movements under load, reinforcing proper joint angles and ground contact patterns.
Final Thoughts
While A- and B-skips are popular components of sprint training, this study shows that they differ significantly from maximal sprinting in terms of joint angles, velocities, and step rate. Coaches that are questioned about their use and efficacy should steer clear of describing them as tools for the improvement of sprint biomechanics. Instead, coaches should present the idea that A- and B-drills are dynamic movement drills that increase the athlete’s capacity to sprint by preparing the body for the explosive demands of sprinting.