Technical Sprinting in the Early Phase of Hamstring Injury Rehabilitation to Accelerate Return to Full Participation in Track and Field Athletes: A Comparative Study of Two Rehabilitation Strategies

Introduction: Hamstring injuries are common in track and field athletes with a higher incidence in males than females. It causes a significant loss in training time and a decline in performance. This study evaluated rehabilitation strategies to accelerate return to full participation following hamstring injury. Methods: Thirty-three athletes (22 males; 11 females) were screened from November 2021 to October 2023 until their final major competition. Out of these, 17 athletes with hamstring injuries were included in this study which were further divided into two groups, A (n=8) and B (n=9), using stratified random sampling with single blinding. Group A received technical sprints using mini hurdles as part of their training from the early stages of rehabilitation, while Group B underwent high-volume low-intensity rehabilitation before progressing to sprints. The progress of each group was monitored on a weekly basis. The average time loss was calculated using Microsoft Excel (Microsoft® Corp., Redmond, WA) and Google Forms (Google, Inc., Mountain View, CA) with built-in validation. Results: The two groups demonstrated a significant difference in recovery times. In group A, the length of hamstring tenderness (LHT) improved from 9 ± 2.7 (95% CI 2.27) to 0.15 ± 0.3 (95% CI 0.62), active total knee extension (ATKE) from 161.8 ± 7.1 (95% CI 5.95) to 175.4 ± 2 (95% CI 2.3), and Numeric Pain Rating Scale (NPRS) in the isometric test from 5.6 ± 1.09 (95% CI 0.88) to 0.6 ± 0.5 (95% CI 0.63) with p<0.05, and in Group B, LHT improved from 6.8 ± 2.1 (95% CI 1.62) to 0.6 ± 0.7 (95% CI 0.55), ATKE improved from 168.7 ± 8.2 (95% CI 6.3) to 178.7 ± 2.7 (95% CI 2.06) and NPRS with resisted isometric test improved from 6 ± 1.4 (95% CI 1.08) to 0.8 ± 0.7 (95% CI 0.51) with p<0.05. However, Group A took an average of 3.55 weeks (1.22 SD 95% CI 1.08) and Group B took an average of 4.53 weeks (1.98 SD, 95% CI 1.52) to resume full participation. Three athletes from Group A and six athletes from Group B experienced hamstring tightness during the competition, two athletes from Group B were forced to withdraw from the competition due to hamstring reinjury. Conclusions: The findings indicate that an early technical sprint program can facilitate an early return to full participation. This research can be a guide toward accelerated and integrated hamstring injury rehabilitation among track and field athletes.


Introduction
Sprinting is a sport that requires exceptional strength and speed.The most prevalent muscle injury in highintensity sprinting is the hamstring which comprises 17% of all injuries in track and field.Studies have consistently demonstrated that male athletes are at a higher risk of injury than female athletes, particularly in the hamstring region [1].These injuries often result in substantial loss of training time and have a detrimental impact on athletic performance.The hamstring reinjury rate is high.Hence, a good hamstring injury rehabilitation program is imperative [2,3].
Additionally, sprint kinematics play a significant role in hamstring injuries and performance.Previous research has evaluated the effect of physiotherapy, strength training, and coaching cues on improving posture and biomechanics, which may contribute to a reduced risk of hamstring injuries during highintensity sprinting [25].The rehabilitation program for hamstring injuries has been extensively researched, however, there is a lack of data regarding effective strategies for promoting an early return to full participation following hamstring injury in track and field athletes.Therefore, this study aims to investigate the effectiveness of incorporating technical sprinting in the early phase of hamstring injury rehabilitation to accelerate return to full participation as compared to isolated exercises in track and field athletes.

Samples
A prospective screening of 33 athletes (22 male and 11 female) was done between November 2021 and October 2023, out of which 17 hamstring injuries were recorded and included in this study.The injured athletes were then divided into two groups based on a coaching strategy using stratified random sampling using single blinding.Group A comprises athletes with a mean age of 21.2 ± 3.2 years, height of 175.9 ± 10.2 cm, and mass of 62.

The athletes' training blocks
The season was structured into several training periods, known as training blocks, which typically consisted of three weeks of training followed by one week of testing and de-loading.These blocks were categorized into several phases, including General Preparation (GP), Specific Preparation (SP), Competition Preparation (CP), and competition (Comp).

Assessment
The clinical examination was done for both groups at baseline and repeated every fourth day until the criteria for full participation was met and three outcome measures were recorded namely the Numeric Pain Rating Scale (NPRS) score during prone hamstring isometric contraction, length of hamstring tenderness (LHT), and active total knee extension (ATKE) range of motion (ROM) in degrees in supine lying with 90 degrees hip flexion.
The NPRS score of hamstring pain was recorded on the injured side during prone isometric contraction hold for five seconds at 90 degrees knee flexion.ATKE ROM was noted at an angle of perceived pain and restriction in the supine lying position with the hip at 90 degrees flexion wherein the athlete was instructed to actively extend the knee.The palpation method was utilized to identify the LHT area over the muscle or tendon to determine the location and extent of injury i.e. medial, lateral, proximal, or distal injury.These outcome measures were monitored on a regular basis to guide the criteria for return to full participation.

Interventions
During the initial stages of the injury, the athletes received relative rest with pain management strategies using various techniques including sports massage, ice, gentle stretching, and icing in both groups.Further management changed from the third day onwards as given below: Group A from the third day onwards, technical training through sprints was introduced, with feedback provided by a coach.The sports physiotherapist present on the field led the identification of predisposing factors such as forward lean [5], spine or sacroiliac joint pathologies [14][15][16], flexibility in the hamstring and lumbopelvic complex [17][18][19][20], and poor conditioning, overtraining, undertraining, excessive stretching, and muscle imbalances [19,[21][22][23][24]. Strength training was included based on training blocks/phases to maintain conditioning.Technical sprints were included along with strength training to prevent overstriding, with the help of mini hurdle runs over 50-60 meters.The cue was to "hit the foot under the hip, within the tolerable pain threshold."Soft tissue therapy and sports massage were used to reduce stiffness and pain post-training.
Athletes were educated to train through pain within the tolerable pain threshold, and supportive care such as taping and strapping was provided if required.Once the pain was reduced, the technical aspect was transferred to flat running with 60 meters, including 20 meters of mini hurdles.The mini hurdles were gradually weaned off as the athlete became more aware of the technical aspects of sprints.Repeated sprints were given in the form of speed endurance, with 60 meters x 5 repetitions into three sets, with one-minute rest between reps and six minutes rest between sets.The decision of intensity increment was based on Table 2, in which the athletes were asked to do technical sprints as per the yellow zone derived within the center.

Red Zone Yellow Zone Green Zone
Pain

TABLE 2: Zones of training
In zones of the training, athletes were educated to use this table to push through the intensity as the symptoms improved.
Group B, from the third day onwards, low-intensity and high-volume, isolated rehabilitation exercises were introduced, which consisted of strength exercises for the hamstring, gluteal muscles, and core.The progression was based on symptoms, starting with isometric exercises, then moving to concentric exercises, and finally to eccentric exercises.Once the participants in Group B met the criteria for a return to full participation, sprinting was introduced.

Zone for training
Zones of training were defined in collaboration with Coaches and Sports Physiotherapist for sprints which primarily included pain levels.The Traffic Light analogy is described in Table 2.

Criteria for return to full participation
Due to the absence of established clinical criteria for determining when track and field athletes are ready to resume full participation, our criteria were based on clinical outcome measures, which included assessments of the extent of the injury, loss of ROM, and pain provocation.These measures were evaluated every fourth day by a physiotherapist to track progress.The criteria were deemed met when the LHT (in cm) was reduced by more than 90%, the ATKE ROM was achieved at 95% or greater compared to the unaffected side, and the NPRS score on the resisted isometric test was less than 1/10.

Statistical analysis
Descriptive statistical analysis was introduced using Microsoft Excel 365 software (paid version, Microsoft® Corp., Redmond, WA), and the mean, standard deviation, and confidence interval were used for analysis.Google Forms (Google, Inc., Mountain View, CA) was used to collect data on a daily basis to analyze the effect of rehabilitation planning and modification in intensity.All Google Forms data were collected in Google Sheet format and later extracted the sheets between 2021 and 2023 and filters were created to track the improvement in various outcome measures, which were then copied into different Excel Sheets and it was analyzed.

Injuries reported in different blocks
The season was structured in different training blocks/phases as mentioned earlier, and different blocks/phases reported hamstring injuries which is described in Table 5.

TABLE 5: Injuries reported in different training blocks/phases
Different blocks/phases of training in which hamstring injuries were reported.This includes GP, SP, and CP.
Both the groups exhibited considerable improvements in LHT, NPRS with the resisted isometric test, and ATKE with a p value of less than 0.05 as shown in Table 6.Group A showed significant improvement between the 24th and 28th day post-injury.LHT improved from 9 ± 2.7 (95% CI 2.27) to 0.15 ± 0.  In ATKE ROM, the baseline data for Groups A and B showed 8.1% and 4.2%, and the final result showed a 1.2% and 1.8% difference compared to the uninjured side respectively.
The difference in the time taken for full participation to be resumed between Group A and Group B was notable, with Group A requiring an average of 3.55 weeks (with a standard deviation of 1.22 and a 95% confidence interval of 1.08) compared to Group B's 4.53 weeks (with a standard deviation of 1.98 and a 95% confidence interval of 1.52).Group A was able to resume full participation one week prior to Group B.
Figure 1 shows the LHT in Groups A and B, and reduction over a period of every fourth day until it achieved the desired return to full participation criteria.

FIGURE 1: Length of hamstring tenderness in Groups A and B
In Figure 1A, the graph represents the length of hamstring tenderness, which improved between the 24th and 28th day from the initial assessment.However, in Figure 1B, the improvement was recorded between the 32nd and 36th day from the initial assessment.Error bars represent the 95% confidence interval of the data.
Figure 2 shows NPRS in resisted isometric hold in Groups A and B, and reduction over a period of every fourth day until it achieved the desired return to full participation criteria.Active total knee extension (ATKE) range of motion (ROM) was measured using a goniometer and the maximum ROM taken was 180 degrees.Figure 3A shows improvement in the overall ROM in Group A which was recorded between the 24th and 28th day; however, in Figure 3B, the improvement was recorded between the 32nd and 36th day post-initial assessment.Error bars represent the 95% confidence interval of the data.
Corresponding to injury reported during the different blocks and reinjury or hamstring tightness reported post-competition are shown in Table 7.In Group B we recorded two re-injury which corresponded to SP and CP, however, the tightness reported post-competition was three and six in Groups A and B respectively as shown in Table 7.

Blocks/Phases Hamstring Injuries
>5/10 during and after and next morning Pain <5/10 during and after but not next morning No pain during, after and next morning Pain on muscle contraction or weak contraction Pain on muscle contraction but strong contraction Pain free contraction or strong contraction Pain with stretch or movement does not respond to therapy Pain with stretch or movement but responds to therapy No pain in stretch or movement >5/10 pain with basic functional activity <5/10 pain with basic functional activity No pain

FIGURE 2 :Figure 3
FIGURE 2: NPRS in resisted isometric hold in Groups A and B Figure 2A represents the NPRS score in Group A and recorded the improvement between the 24th and 28th day; however, Figure 2B recorded the improvement between the 32nd and 36th day which represents the NPRS score in Group B. The error bars represent a 95% confidence interval.NPRS: Numeric Pain Rating Scale

FIGURE 3 :
FIGURE 3: Active total knee extension (ATKE) range of motion (ROM) inGroups A and B 5 ± 11.0 kg, and Group B comprises athletes with a mean age of 20.31 ± 3.19 years, height of 173.21 ± 8.25 cm, and mass of 61.88 ± 7.9, with no statistical baseline difference among groups p>0.05.Athletes who included sprinting as part of their training program were included in this study and competed in national-level competitions organized by the National Federation.The athlete characteristics are presented in Table 1.

Table 4 ,
with no significant difference between the groups (p>0.05).
NPRS: Numeric Pain Rating Scale; LHT: length of hamstring tenderness; CI: confidence interval

TABLE 6 :
ResultsLHT: length of hamstring tenderness; NPRS: Numeric Pain Rating Scale, ATKE (ROM): active total knee extension range of motion; # indicates mean; * indicates standard deviation (+ or -), CI: confidence interval at 95%; p value of less than 0.05 is taken as statistically significant.