Isokinetic exercise combined with blood flow restriction (BFR) may produce a greater change in the angle of peak torque

Isokinetic exercise combined with blood flow restriction (BFR) may produce a greater change in the angle of peak torque

GÖKHAN BÜYÜKLÜOĞLU1, BIHTER AKINOĞLU2, HÜSEYIN GÜNAYDIN1, İSMAIL KÜÇÜK1, AYDAN ÖRSÇELIK1, TUĞBA KOCAHAN1

1Department of Sports Medicine, Gülhane Training and Research Hospital, Ankara, Turkey; 2Faculty of Health Science, Physiotherapy and Rehabilitation Department, Yıldırım Beyazıt University, Ankara, Turkiye.

Summary. Background. Blood flow restricted (BFR) training represents a new approach to exercise. The angle of peak torque (APT) is the joint angle at which a muscle reaches maximal torque, measured with an isokinetic dynamometer. Time to peak torque (TPT) is the duration until the point above is reached. This study aimed to examine the impact of isokinetic training with BFR on APT and TPT. Methods. The data of two groups of patients who underwent knee concentric exercise on the isokinetic device were utilized. One group consisted of isokinetic exercise combined with BFR and the other group consisted of concentric isokinetic exercise only. The assessments of APT, TPT, and peak torque/body weight (PT/BW) for both knee flexor muscles were conducted using an isokinetic dynamometer at angular velocities of 60º and 180º/sec. Results. Before the implementation of the exercise protocols, no significant difference was observed between the BFR and control groups concerning APT, TPT, and PT/BW values at speeds of both 60º and 180º/sec angular velocities (p>0.05). After the completion of the exercise protocol, the APT of flexion at 60º/sec angular velocity exhibited a more pronounced decline in the BFR group relative to the control group. (p= 0.017). Conclusıons. As BFR can affect different fiber types by different mechanisms, it may have caused a change in APT even though it made no difference to peak torque. This may also signify a comparatively substantial augmentation in the eccentric strength, but further research is needed to confirm these assumptions.

Key words. Blood flow restricted training, angle of peak torque, time to peak torque, isokinetic exercise.

L’esercizio isocinetico combinato con la restrizione del flusso sanguigno (BFR) può produrre una maggiore variazione nell’angolo di coppia massima

Riassunto. Background. L’allenamento con restrizione del flusso sanguigno (BFR) rappresenta un nuovo approccio all’esercizio fisico. L’angolo di piccola coppia (APT) è l’angolo articolare al quale un muscolo raggiunge la coppia massima, misurata con un dinamometro isocinetico. Il tempo al picco di coppia (TPT) è la durata necessaria per raggiungere tale punto. Questo studio esamina l’impatto dell’allenamento isocinetico con BFR su APT e TPT. Metodi. Sono stati analizzati i dati di due gruppi di pazienti sottoposti a esercizi concentrici del ginocchio su dispositivo isocinetico. Un gruppo ha svolto esercizi isocinetici associati a BFR, mentre l’altro gruppo ha eseguito solo esercizi concentrici isocinetici. Le valutazioni di APT, TPT e della coppia di picco/peso corporeo (PT/BW) per entrambi i muscoli flessori del ginocchio sono state effettuate utilizzando un dinamometro isocinetico a velocità angolari di 60º e 180º/sec. Risultati. Prima dell’applicazione dei protocolli di esercizio, non sono state osservate differenze significative tra i gruppi BFR e di controllo in riferimento ai valori di APT, TPT e PT/BW alle velocità angolari di 60º e 180º/sec (p>0,05). Dopo il completamento del protocollo di esercizio, l’APT in flessione alla velocità angolare di 60º/sec ha mostrato una riduzione più marcata nel gruppo BFR rispetto al gruppo di controllo (p=0,017). Conclusioni. Poiché il BFR può influenzare diversi tipi di fibre muscolari attraverso differenti meccanismi, potrebbe aver determinato una variazione nell’APT pur non modificando la coppia massima. Questo potrebbe indicare anche un potenziamento relativamente maggiore della forza eccentrica, ma sono necessarie ulteriori ricerche per confermare tali ipotesi.

Parole chiave. Allenamento con restrizione del flusso sanguigno, angolo della coppia massima, tempo al picco di coppia, esercizio isocinetico.

Introduction

Blood flow-restricted (BFR) training represents a relatively novel approach to exercise. In this method, partial obstruction of blood flow is achieved by applying a band or cuff to the proximal arm or leg1. The objective of this technique is to achieve outcomes comparable to those of high-intensity exercises with low resistance2,3. This can be particularly advantageous in rehabilitation processes and in preventing muscle loss in elderly individuals, as well as providing an alternative method for athletes who do not have the opportunity to perform high-intensity training. It has been shown to positively impact muscular strength, endurance, and overall performance, while also speeding up the healing process1-3.

Long-term physical activity gives rise to alterations in the moment–angle relationship of the human skeletal muscles. This relationship can be evaluated in vivo by isokinetic tests4. (Alegre et al., 2014) Angle of peak torque (APT) represents the joint angle at which any given muscle reaches its peak torque. This measurement can be obtained through the use of an isokinetic dynamometer5. Time to peak torque (TPT) is the duration of time until the previously mentioned point is reached5.

The strength of the knee flexor muscles is a crucial determinant of performance in activities such as sprinting, jumping, and rapid changes in direction5. The knee flexor peak torque angle indicates the specific joint angle at which the hamstring muscles are capable of generating maximal torque output. The significance of knee flexor peak torque angle lies in its potential applications in enhancing sports performance, preventing injuries, optimizing rehabilitation processes, and biomechanical analysis. Furthermore, the knee flexor peak torque angle has been identified as a predictor of injury risk and a measure of return to play in the context of hamstring injuries5-7. Alterations in the moment–angle relationship towards longer muscle lengths have been associated with a reduced risk of injury in the knee flexor and extensor muscles, as the sarcomeres of the muscle operate near the plateau of their length-tension curves for a greater portion of the joint range of motion4.

The objective of this study was to examine the impact of concentric knee flexion/extension training with an isokinetic dynamometer in conjunction with BFR on APT and TPT.

Patients and methods

Participants and study design

The study was designed retrospectively. Following the approval of Ankara Yıldırım Beyazıt University Ethics Committee with decision number 06-774 on 07.06.2024, the requisite institutional permissions for the study were obtained. The study has been conducted in accordance with the principles set forth in the Helsinki Declaration. The data of recreational and professional athletes who underwent knee concentric exercise on the isokinetic device for various reasons between 01/01/2019 and 01/06/2024 in Health Sciences University Gülhane Training and Research Hospital Sports Medicine Clinic were utilized. The patients were divided into two groups: one comprising those who had undergone combined exercise with continuous BFR and the other, those who had only undergone concentric isokinetic exercise.

To be included in the study, patients had to meet the following criteria: they had to have complete and accessible data for both groups, they had to be aged 18 or over, and they had to have exercised on the isokinetic device for a minimum of 6 weeks and a maximum of 8 weeks.

Procedure

In the BFR group, the application was performed using a Biodex IV (USD) isokinetic dynamometer device and a KAATSU C3 cuff. The pneumatic cuff was attached to the proximal thighs of the participants. Arterial occlusion pressures were determined with a Doppler device from the dorsalis pedis artery in the isokinetic dynamometer test position. Isokinetic protocol was applied with 80% of the occlusion pressure because it provides more strength and less fatigue8.(Kose et al., 2023)The maximum duration of the BFR protocol was 20 minutes. In the control group, the exercise protocol was administered without any restriction on blood flow.

Isokinetic dynamometer training was performed 2 times a week for a total of 6-8 weeks, 3 sets of 10 repetitions at a speed of 60º/sec and 3 sets of 30 repetitions at a speed of 180º/sec. The rest between the sets was 30 seconds. It was ensured that there was at least one day gap between training days. Prior to training, the athletes engaged in a 10-minute warm-up cycle on a bicycle ergometer, maintaining a pedaling speed between 60 and 80 revolutions per minute (rpm).

The peak torque angle of the knee flexor muscles was measured using a Biodex IV (USD) isokinetic dynamometer. The strength of both knee flexor muscles was assessed concentrically using an isokinetic dynamometer at angular velocities of 60º and 180º/sec with 5 and 15 repetitions, respectively. Before each angular velocity, 3 repetitions of the exercise were performed to understand the movement and to warm up.

Statistical analysis

The data gathered from this study were analyzed utilizing the SPSS (Statistical Package for the Social Sciences) version 23 software. The mean, standard deviation, confidence intervals, and median were calculated for quantitative variables, while frequencies (n) and relative frequencies (percentages) were determined for qualitative variables. Intergroup comparisons were conducted using the chi-square test for categorical variables, the t-test for independent variables, and the paired samples t-test for dependent variables9. The results were evaluated at the 0.05 significance level.

Results

The isokinetic test values of 64 extremities belonging to 32 participants (17 females and 15 males) were subjected to analysis. A total of 36 extremities completed the combined isokinetic exercise protocol with BFR, while 28 extremities completed only the isokinetic exercise protocol.

The chi-square test revealed no significant difference between the BFR and control groups in terms of gender (p=0.801). There was no statistically significant difference in anthropometric measurements (height, weight and body mass index) between the BFR and control groups (p=0.985, p=0.986, p=0.981, respectively). Furthermore, no significant differences were observed when the BFR and control groups were compared in terms of mean age or peak torque/bodyweight at 60 and 180 degrees/sec angular velocity (p=0.240, p=0.301, p=0.166, respectively) (table 1).

The results of the comparison between the groups are presented in table 2, while the comparison of the groups within themselves over time is illustrated in table 3.

Discussion

Numerous studies in the literature examine how eccentric exercise protocols can positively influence hamstring APT10-13. In this study, unlike these studies, the effect of BFR application on APT, TPT, and PT/BW values in addition to concentric isokinetic exercise protocol was investigated. At the beginning of the study, no statistically significant difference was observed between the BFR and control groups with regard to APT, TPT, and PT/BW values for both angular velocities.

The most significant outcome of this investigation was the observation that the alteration in the peak torque angle of flexion at 60º/sec in the BFR combined group exhibited a more pronounced decline than that observed in the control group. With this decline, the peak torque angle shifted closer to knee extension and reached a longer muscle length. It has been demonstrated that shifting the peak torque angle to the longer muscle state is frequently observed in the case of eccentric hamstring training exercises12,14,15.

In contrast to the aforementioned studies, this study achieved this outcome through the utilization of concentric isokinetic hamstring exercises. Furthermore, the BFR combined group exhibited a statistically significant advantage over the control group. It is not possible to ascertain whether the BFR or control groups would prove more efficacious than the eccentric exercise groups, as they were not included as a third group in the study. Nevertheless, given that alterations of up to 42% have been documented in the existing literature, this study observed a change of 41% for 60º/sec flexion APT when considering the averages of all participants12. It has also been shown in the study below that this development can be a result of several different training methods being in use.

In Matthews et al. study, demonstrated that a soccer-specific fatigue program resulted in acute displacement of APT to a shorter muscle size. Furthermore, they proved that this change could be attenuated by hamstring training, which was administered in two different forms: one focusing on strength and the other on endurance10.

Coratella et al. evaluated peak joint torque angle before and after a fatigue protocol application. Their findings indicated that the APT for flexion of the hamstrings increased after the fatigue protocol, suggesting a shorter muscle position. However, they reported that a similar result was not observed for the quadriceps muscle13. It was proposed that this outcome may be attributable to the disparate fiber composition of the hamstring and quadriceps muscles. The hamstring muscles are characterized by a greater prevalence of fast-twitch fibers, which exhibit low endurance and high fatigability16. Given the existing literature on quadriceps muscle and the prevalence of hamstring strains, this study focused exclusively on flexion values. The difference observed at 60º/sec was not evident at 180º/sec, which may be attributed to the impact of BFR on the hypertrophy of diverse fiber types.

In the hamstring muscle group, the capacity to resist the concentric contraction of the quadriceps muscle is reduced due to fatigue, and the flexion peak torque angle increases17. This results in a shift away from extension and towards a shorter muscle state. This biomechanical basis for the increased incidence of hamstring strain at the end of competitions is therefore evident13,17. Consequently, any intervention to minimize these changes may ultimately serve to reduce hamstring injuries. Given the prevalence of hamstring strains as a cause of injury and absence from sports, particularly in sprint-based disciplines, the value of preventive programs becomes evident10. This study suggests that BFR combined isokinetic exercise may be useful in preventing hamstring strains, as an alternative to eccentric exercises that are already known to be useful. However, this idea needs to be supported by further clinical trials.

A review of the literature indicates that studies show a combined BFR and high-resistance exercise regime is not superior to an isolated high-resistance exercise regime18. The results of this study corroborate this finding with respect to the PT/BW value. However, the combination of isokinetic exercise with BFR may result in the hypertrophy and strength increase of different muscle fibers, which may explain the observed difference in the 60º/sec flexion APT value.

Strengths and limitations of the study: BFR combined exercise that was performed for at least 6 weeks and the presence of a control group are the strengths of the study. The absence of a notable discrepancy between the BFR and control groups with regard to gender, age, and PT/BW at the outset is a noteworthy aspect, as it demonstrates the homogeneity and similarity of the two groups. The study’s limitations are attributed to its relatively small sample size and the absence of an eccentric exercise, intervention, or measurement.

Conclusions

The findings demonstrate that both the BFR combined and isolated isokinetic concentric strength protocols result in a reduction in APT and TPT values and an increase in PT/BW values. It is noteworthy that the BFR combined concentric isokinetic exercise with 80% AOP has been observed to result in a greater reduction in peak torque angle at 60º/sec than that achieved by the isolated isokinetic exercise. This may indicate an enhancement in eccentric strength, but this needs to be supported by further studies. The findings of this study may inform the decision-making process regarding the implementation of BFR training in the context of sports performance enhancement.

Conflicts of interest. The authors declare that there is no conflict of interest.

Authors’ contributions. GB and HG have given contributions to the conception and the design of the manuscript, BA to interpretation of the data. GB, AO and TK have participated to drafting the manuscript and final revision. All authors read and approved the final version of the manuscript.

References

1. Büyüklüoğlu G, Akkaya Z, Özer O, Kaya İ, Gül S, Çelebi M. A validity and reliability study of pressure prescription methods for upper extremity blood flow restriction training. Gazzetta Medıca Italıana Archıvıo per le Scıenze Medıche 2024; 183.

2. Scott BR, Loenneke JP, Slattery KM, Dascombe BJ. Exercise with blood flow restriction: an updated evidence-based approach for enhanced muscular development. Sports Med 2015; 45: 313-25.

3. Patterson SD, Hughes L, Warmington S, et al. Blood flow restriction exercise: considerations of methodology, application, and safety. Front Physiol 2019; 10: 533.

4. Alegre LM, Ferri-Morales A, Rodriguez-Casares R, Aguado X. Effects of isometric training on the knee extensor moment–angle relationship and vastus lateralis muscle architecture. Eur J Appl Physiol 2014; 114: 2437-46.

5. Nishida S, Tomoto T, Maehara K, Miyakawa S. Acute effect of low-intensity eccentric exercise on angle of peak torque in subjects with decreased hamstring flexibility. Int J Sports Phys Ther 2018; 13: 890.

6. Centner C, Jerger S, Lauber B, et al. Similar patterns of tendon regional hypertrophy after low‐load blood flow restriction and high‐load resistance training. Scand J Med Sci Sports 2023; 33: 848–56.

7. Timmins RG, Shield AJ, Williams MD, Opar DA. Is there evidence to support the use of the angle of peak torque as a marker of hamstring injury and re-injury risk? Sports Med 2016; 46: 7-13.

8. Kose DE, Aksit T, Akyildiz ZI, Erman B, Ozkol MZ, Vural F. The acute effects of different percentages of blood flow restrictions on all-out back squat exercise. Medicina dello Sport 2023; 76: 319-32.

9. Fagerland MW. T-tests, non-parametric tests, and large studies: a paradox of statistical practice? BMC Med Res Methodol 2012; 12: 1-7.

10. Matthews MJ, Heron K, Todd S, et al. Strength and endurance training reduces the loss of eccentric hamstring torque observed after soccer specific fatigue. Phys Ther Sport 2017; 25: 39-46.

11. Maciel DG, Dantas GAF, Cerqueira MS, et al. Peak torque angle, acceleration time and time to peak torque as additional parameters extracted from isokinetic test in professional soccer players: a cross-sectional study. Sports Biomech 2023; 22: 1108-19.

12. Delextrat A, Bateman J, Ross C, et al. Changes in torque-angle profiles of the hamstrings and hamstrings-to-quadriceps ratio after two hamstring strengthening exercise interventions in female hockey players. J Strength Cond Res 2020; 34: 396-405.

13. Coratella G, Bellin G, Beato M, Schena F. Fatigue affects peak joint torque angle in hamstrings but not in quadriceps. J Sports Sci 2015; 33: 1276-82.

14. Clark R, Bryant A, Culgan JP, Hartley B. The effects of eccentric hamstring strength training on dynamic jumping performance and isokinetic strength parameters: a pilot study on the implications for the prevention of hamstring injuries. Phys Ther Sport 2005; 6: 67-73.

15. Cohen DD, Zhao B, Okwera B, Matthews MJ, Delextrat A. Angle-specific eccentric hamstring fatigue after simulated soccer. Int J Sports Physiol Perform 2015; 10: 325-31.

16. Garrett Jr WE, Califf JC, Bassett FH. Histochemical correlates of hamstring injuries. Am J Sports Med 1984; 12: 98-103.

17. Hawkins RD, Hulse MA, Wilkinson C, Hodson A, Gibson M. The association football medical research programme: an audit of injuries in professional football. Br J Sports Med 2001; 35: 43-7.

18. Dankel SJ, Buckner SL, Jessee MB, et al. Can blood flow restriction augment muscle activation during high‐load training? Clin Physiol Funct Imaging 2018; 38: 291-5.