Random thoughts on the latest research on hamstrings injuries and programming

"If You Want to Prevent Hamstring Injuries in Soccer, Run Fast: A Narrative Review about Practical Considerations of Sprint Training"

Pedro Go?mez-Piqueras and Pedro E. Alcaraz (2024)

This paper effectively summarizes key aspects of sprinting in football, offering valuable insights into periodization strategies, monitoring sprinting, and defining appropriate dosage. One of the highlights is the mention of MD-2 as the "most tactical" and "speed" day of the week. However, as the authors point out, the accumulated load from MD-4 and MD-3 can negatively impact a player's performance and potentially increase the risk of injury on MD-2.

When defining a player's reaction to this load and its impact, we need to consider the player's "battery"—their physical state on that day. It's crucial to understand both the game demands and position-specific demands for that player, as the study emphasizes. Knowing the acute and chronic loads the player is exposed to is paramount. Between these two categories, training sessions and drills selected by coaches play a key role in developing or addressing game situations.

In Croatia, it's common to place significant focus on tactical actions on MD-2, but we must also consider how to best use the first day of the week and other training days to provoke adaptations and simulate game demands. While the total number of sprints and distances covered in specific speed zones are valuable, I have always been more interested in the distribution of these actions and the specific situations in which they occur. It's important to examine the frequency of these actions and how often they happen during games. Furthermore, I want to understand what kind of actions precede these high-intensity efforts and the movements players make before transitioning into them.

Lets use one game scenario

Overview of Key Metrics:

• Average Sprint Distance: 93.72 meters – This is the average distance covered by the players in sprinting zones (Zone 5).
• Average HSR (High-Speed Running) Distance: 379.6 meters – The average distance players covered in high-speed running.
• Intensity: 7.08 – This value likely reflects the intensity of the match, calculated from factors such as distance, speed, and workload.

Selected Player Data:

Below are the metrics collected for individual players based on the selected variables in the dashboard.

1. Player 1:

• Total Distance: 7848.05 meters
• Total Duration: 90.48 minutes
• Sprint Distance (Zone 5): 231.45 meters
• HSR Distance (Zone 4): 604.89 meters
• Meters per minute: 84.39 m/min
• Max Velocity: 31.57 km/h
• Accelerations (Zone 4): 8
• Decelerations (Zone 4): 26

1. Player 2:

• Total Distance: 10783.96 meters
• Total Duration: 108.68 minutes
• Sprint Distance (Zone 5): 201.7 meters
• HSR Distance (Zone 4): 653.36 meters
• Meters per minute: 93.77 m/min
• Max Velocity: 29.88 km/h
• Accelerations (Zone 4): 2
• Decelerations (Zone 4): 7

As you can see, when we compare the frequency of actions and the total volume in individual variables, player 1 and player 2 are very similar in most aspects. Both players have comparable values in terms of total distance, sprint distance, and high-speed running distance. However, there is a noticeable difference in the number of high-intensity accelerations and decelerations, where player 1 has significantly more of these actions compared to player 2. This suggests that while their overall physical output during the match is similar, player 1 was involved in more intense stop-start actions, which could indicate a difference in their roles or positioning on the field.

Let's take it a step further and analyze what happens with these two players in the raw data. It is already visually apparent that these activities are distributed differently throughout the match. However, to avoid complexity with graphs, I will attempt to present this in a table format with values in the next display.

To analyze the frequency of actions, duration, and distance covered, along with the profiles of Player 1 and Player 2, let's break it down into several key components (have in mind, i just took first 15 minutes of the match and just for efforts above 19.8km/h):

1. Frequency of Actions

• The frequency of actions refers to how often high-speed or sprint efforts occurred for each player during the match. Both players have their efforts spread across different times, as shown by the Start Time and End Time columns.

For Player 1:

• The high-speed actions are relatively frequent, with intervals between efforts typically ranging from a few seconds to several minutes.
• Example: Between 4m 28s and 10m 16s, there is approximately a 6-minute gap, showing a recovery or rest period between those high-speed efforts. In contrast, between 12m 13s and 13m 28s, the gap is shorter (about 1 minute).

For Player 2:

• Similarly, Player 2 has frequent actions, but the intervals between efforts vary slightly more, with some actions happening back-to-back within seconds and others spaced by several minutes.
• Example: Between 4m 28s and 12m 11s, there is a nearly 8-minute gap, but between 12m 13s and 12m 15s, actions occur within just 2 seconds.

2. Duration of Actions

Both players have high-intensity actions that mostly last for 1 second (with some very brief bursts measured as 0.5 seconds).

For Player 1:

• Actions typically last 1 second (e.g., Vmax of 29.88 km/h over a duration of 0m 1s).
• Some efforts are exceptionally brief, lasting only 0 seconds, which likely represents very sharp bursts of speed that are difficult to measure at longer intervals.

For Player 2:

• Similarly, most actions last 1 second, showing that Player 2 also performs short, sharp sprints (e.g., Vmax of 28.8 km/h over 0m 1s).

3. Distance Covered

The distance covered in each high-speed action is crucial for understanding the intensity of the efforts.

For Player 1:

• Distance ranges from 3.68 meters to 16.69 meters during high-speed efforts.Example: At 4m 28s, Player 1 covers 11.31 meters with a Vmax of 29.88 km/h.

For Player 2:

• Distance varies from 3.68 meters to 11.99 meters.Example: At 4m 28s, Player 2 covers 7.88 meters with a Vmax of 28.8 km/h.

This suggests that Player 1 covers slightly more distance per effort on average, especially in the higher velocity zones.

4. Profile Before Reaching Max Velocity (T-1s, T-2s, T-3s)

The columns T-1s, T-2s, and T-3s represent the velocity in the 1, 2, and 3 seconds leading up to the max velocity. This helps show how quickly players accelerate before hitting their peak speed.

For Player 1:

• T-1s (1 second before max velocity) values are typically around 21-26 km/h, suggesting a gradual acceleration.Example: At 4m 28s, T-1s is 28.8 km/h, which shows a very steep acceleration just before hitting Vmax.
• T-2s and T-3s are slightly lower, typically in the range of 16-20 km/h, indicating a smooth buildup of speed.

For Player 2:

• T-1s values are similar, usually around 21-27 km/h, with more consistent accelerations across efforts.Example: At 4m 28s, T-1s is 29.88 km/h, showing a rapid buildup right before the sprint.

This suggests both players have similar acceleration profiles, but Player 1 may engage in sharper increases in speed before hitting their max velocity in certain efforts.

5. Recovery Durations Between Actions

Recovery durations (the time between high-speed efforts) are critical to understanding how players are distributed across phases of activity.

For Player 1:

• Recovery between actions varies significantly, with rest periods ranging from 1 second to 8 minutes.Example: The gap between 4m 28s and 10m 16s is around 6 minutes, indicating a prolonged rest after a burst of sprinting.

For Player 2:

• Similarly, the recovery periods vary from a few seconds to several minutes.Example: Between 4m 28s and 12m 11s, there is a nearly 8-minute gap.

6. Defining the Profile or Coefficient of Activity

We can define a sprint-to-recovery coefficient to represent the ratio of sprint efforts to recovery time. This will give us an idea of how often a player engages in high-intensity actions relative to their recovery.

For Player 1:

• With 54 records of efforts, and assuming an average match time of around 90 minutes, Player 1 performs a high-speed effort approximately every 1.67 minutes (or once every 100 seconds).
• However, the wide variability in recovery time (from seconds to minutes) suggests a mixed sprint profile, with some periods of intense back-to-back sprints and others of prolonged recovery.

For Player 2:

• With 55 records, Player 2 performs a high-speed effort roughly every 1.64 minutes, similar to Player 1.
• The distribution of recovery periods is also varied, but Player 2 tends to perform slightly more frequent but shorter sprints, with more consistent recovery times.

Conclusion:

• Player 1 engages in longer, more explosive sprints, covering more distance per effort, with slightly longer recovery periods between high-speed efforts.
• Player 2 performs shorter sprints more frequently, with consistent bursts of speed but covering less ground per effort.

To summarize, Player 1 seems to play a role that requires intense, sustained high-speed efforts with occasional long recovery periods, while Player 2 demonstrates a more consistent sprint profile, engaging in shorter sprints with more balanced recovery times. The sprint-to-recovery coefficient for both players is similar, but the nature of their high-speed actions suggests different tactical responsibilities on the field.

Why This Analysis is Important:

The detailed analysis of frequency of actions, duration, distance covered, and pre-velocity profiles offers insights that go far beyond simply summing up the total workload. Understanding when and how these high-speed efforts occur provides a clearer picture of the players' physical demands during the game. Here's why this is crucial:

1. Context Matters:Summing total loads (e.g., total distance covered, number of sprints) can provide a basic idea of workload, but it lacks the context of how these efforts are distributed. Two players might cover the same distance or perform the same number of sprints, but the way these efforts are spread throughout the match (frequency, intensity, and duration) can tell us vastly different things about their performance and recovery needs. For example, Player 1 tends to have longer recovery periods between high-speed actions, allowing them to engage in more explosive and sustained sprints. Meanwhile, Player 2 performs shorter but more frequent sprints, indicating they may be involved in a more consistent, high-tempo role. These differences affect how each player should be managed in training and recovery.
2. Fatigue Management: Simply summing up total loads can lead to misinterpretation of fatigue. A player who performs frequent sprints with shorter recoveries (like Player 2) will experience a different kind of fatigue compared to a player who has long recovery periods but performs more explosive efforts (like Player 1). Thus, analyzing effort distribution and rest times helps determine when and how fatigue might accumulate, ensuring we can prevent injuries and improve performance.
3. Game Demands:Understanding the exact nature of a player's actions provides insights into their tactical role. Player 1 may be a player who is called upon for sudden, powerful bursts (e.g., a winger or a forward making long sprints), while Player 2 could be a midfielder who engages in frequent but shorter bursts to cover more ground in a box-to-box role. Knowing when and how these actions happen allows coaches to align training with game demands, ensuring players are prepared for the specific stresses they’ll face in competition.

Training Suggestions for the Microcycle:

To effectively train these two players and tailor their preparation for upcoming games, we need to consider their unique profiles and adjust the microcycle accordingly.

For Player 1 (Longer Sprints with More Recovery):

Focus: Player 1 excels in longer, high-speed efforts with more recovery between actions. The training should aim to maintain or enhance this explosive capability while managing the player's recovery.

1. Early Week (MD-5/MD-4): Speed Endurance Sessions: Include long sprint intervals (e.g., 40-60 meters) with long recovery periods (e.g., 90 seconds to 2 minutes). Focus on maintaining maximum velocity throughout the sprints. Strength Training: Target power development in the gym (e.g., Olympic lifts, plyometrics) to support the explosive bursts seen in matches.
2. Mid-Week (MD-3/MD-2):Sprinting under Fatigue: Set up tactical drills that force Player 1 to sprint after engaging in technical or small-sided games. These should mimic the need to perform explosive sprints even when fatigued, similar to game conditions. Acceleration and Deceleration Training: Shorter sprints focusing on quick changes of direction and high-speed decelerations to build strength in these movements.

For Player 2 (Frequent, Shorter Sprints with Less Recovery):

Focus: Player 2 needs training that supports frequent bursts of effort with shorter recovery periods. The training should focus on high-intensity interval training and endurance-based drills to simulate frequent actions in a game.

1. Early Week (MD-5/MD-4):Repeated Sprint Ability: Use shorter sprints (10-30 meters) with limited recovery (15-30 seconds). The goal is to maintain high-speed efforts across multiple repetitions to mirror the frequent sprints seen in the match. Aerobic Power: Include high-intensity interval training (HIIT) to enhance the player’s ability to recover quickly between bursts of effort. This could involve repeated small-sided games or shuttle runs.
2. Mid-Week (MD-3/MD-2):Small-Sided Games: Tactical drills that involve frequent changes in intensity and short sprints in tight spaces. This simulates Player 2’s need to perform many sprints with minimal recovery during games. Endurance-Based Sprints: Include shuttle runs that work both aerobic and anaerobic systems, focusing on repeatability rather than pure maximum speed.

Summing total loads does not give us the full picture of a player's demands and physical state. By analyzing the context—frequency of actions, recovery durations, and effort profiles—we gain a more accurate understanding of a player's workload and needs. Player 1 and Player 2 have different tactical roles and physical profiles, and their training should reflect that. A tailored approach in the microcycle ensures that both players are prepared for the specific challenges they will face during competition, whether it's frequent, short sprints or explosive, long-distance bursts.

The dendrogram shown in the graph is a hierarchical clustering visualization, which organizes the 10 players (not real data) based on their activity profiles and metrics.

1. Dendrogram Structure:

• The x-axis lists the players in numerical order.
• The y-axis represents the dissimilarity between players, with greater vertical distances indicating more differences between players’ activity profiles.
• The dendrogram begins with each player as its own cluster and merges them step by step, starting from the most similar pairs of players to the least similar.

2. Hierarchical Grouping:

• Players who are connected lower on the y-axis are more similar to each other in terms of their sprint, velocity, rest interval, and acceleration profiles.
• For example, Player 1 and Player 3 are clustered together at a low level, suggesting that they have similar training demands. They are then grouped with Player 8, showing a slightly higher difference, and finally merged with other players in Cluster 1.
• Player 7 and Player 4 form another group with Player 5, suggesting that these players have different demands compared to players in Cluster 1.

3. Cluster Analysis:

• The colors in the dendrogram represent the three clusters formed based on similarities. These clusters can be interpreted as groups of players who have:Similar sprint and velocity patterns.Similar rest intervals between efforts, orSimilar acceleration profiles before reaching maximum velocities (T-1s, T-2s, T-3s).
• Cluster 1 (orange lines): Represents players who tend to have longer sprints, higher velocities, and longer recovery intervals between high-intensity efforts.
• Cluster 2 (red lines): Represents players with more frequent, shorter sprints and less rest between high-speed actions.

4. Practical Use:

• The dendrogram helps identify groups of players with similar demands, allowing coaches to tailor training programs according to the specific needs of each cluster.
• For example, Cluster 1 might include players who rely more on explosive bursts of speed with ample recovery time, while Cluster 2 players might need more work on their endurance and repeated sprint ability.