A comparative study of the acute effects of knee brace vs. kinesiotape on selected isokinetic strength variables of the knee muscles

Abstract

BACKGROUND:

Different methods of treatment for preventing knee injuries, enhancing knee strength and minimising post-injury risks have been explored. Among these methods, Kinesio tape (KT) and knee braces (KB) are commonly used.

OBJECTIVE

: To investigate the acute effects of KT and KB on isokinetic knee strength parameters.

METHODS:

A total of 15 healthy sedentary male subjects voluntarily participated in the study. Concentric isokinetic knee extension (EX) and flexion (FLX) strength were measured at three sessions: 1. Baseline 2. with KT (’KT’) 3. with KB (’KB’). Tests were performed at 60, 180 and 240 ${}^{\circ}$ /s. Peak moment (PM), Hamstring/Quadriceps ratio (HQR), and joint angle at peak moment (JAPM) were measured.

RESULTS:

‘KT’ and ‘KB’ were associated with increase in PM ${}_{\text{EX}}$ , PM ${}_{\text{FLX}}$ , HQR at 60 and 240 ${}^{\circ}$ /s ( $p<$ 0.05) and increased JAPM ${}_{\text{EX}}$ . No significant difference was observed at 180 ${}^{\circ}$ /s ( $p>$ 0.05).

CONCLUSION:

In healthy individuals, ‘I’ shape KT and KB positively affect EX and FLX strengths and HQR, especially at low angular velocity.

Keywords

Strength imbalance acceleration time isokinetic H/Q ratio

1. Introduction

Physically active individuals who participate in recreational, amateur, or professional level activities continually look for recourses or new methods to enhance their muscle strength and prevent injuries [1]. Knee injuries are known to account for up to 60% of all sport injuries, while anterior cruciate ligament (ACL) accounts for almost 50% of knee injuries not excluding others such as meniscal injuries and patello-femoral pain [2, 3]. One of the primary causes of knee injury is the knee joint taking a position contrary to its structure during movement because of strength imbalance in the muscles affecting knee strength [4, 5].

Different methods and treatments are being tested by researchers to prevent knee injuries, enhance knee strength and minimise post-injury risks. Among these methods, Kinesio tape (KT) and knee braces (KB) are the widely applied methods [3, 6, 7, 8]. At present, KT is being extensively used by athletes, physiotherapists and researchers because it has been shown to influence inflammation by increasing blood and lymph circulation, thus stimulating movement as a result of intense contraction in the muscle, reducing pain by decreasing the pressure on subcutaneous nociceptors and facilitating movement in joint and muscle functions by muscle alignment and activation [9, 10, 11, 12, 13]. KT is highly elastic (up to 75% of its original length) depending on the contraction and direction of movement of the muscle group to which it is applied [9, 14]. However, KB has been available for the last 40 years and has been used to help individuals with knee injuries, specifically ACL-reconstructed knees [15, 16, 17]. Moreover, studies have been conducted on KB in relation to physical performance and knee injuries, but these studies generally focused on soccer players. These studies examined the effects of KB on the tendency, severity and incidence of knee injury during physical performance, but they did not indicate any positive finding [18, 19]. Teitz et al. [19] reported that the group using KB was more disabiled than the non-users. In addition, researchers who have examined the effect of KB on neuromuscular activities of the knee joint reported that the use of KB reduced such activity, especially in the quadriceps muscles, but did not reduce the strength by providing a mechanical support to the patellofemoral joint [16, 17].

However, there is still no consensus on whether KT and KB have positive effects in terms of performance [6, 13, 15]. In terms of KT, the reason for this may be that although there are different taping methods, subjects are tested by applying only one taping method to different muscles, especially to the quadriceps (Q) and the hamstring (H) while in terms of KB, it may be attributed to the limited number of studies conducted and the different brands and structures of KB [3, 6, 8, 10, 14, 15, 16, 17, 18, 19, 20, 21, 22].

Therefore this study aimed at investigating the acute effects of ‘I’ shape KT on Rectus Femoris (RF) and the application of KB on isokinetic knee strength, the HQR and the angle of peak moment (JAPM).

2. Methods

2.1 Participants

Fifteen healthy sedentary male subjects (mean age $=$ 22.80 years; mean height $=$ 177.60 cm; mean weight $=$ 70.0 kg) without previous knee injuries voluntarily participated in this study (Table 1). A priori test with GPower 3.1 was used to determine the number of subjects. The power analysis test was conducted following a pilot application which indicated that 12 subjects were sufficient (Effect size: 0.83, Actual power: 0.97); however, to increase the reliability of study and decrease possible risks, the study was conducted with 15 subjects. The study was approved by the Clinical Research Ethics Committee of Gaziantep University (2019/392) and was conducted in accordance with the Declaration of Helsinki.

Table 1
Descriptive parameters of subjects

Variables	Mean	Std. deviation
Age (years)	22.80	1.48
Height (cm)	177.60	7.75
Weight (kg)	70.00	5.96

Figure 1.

Comparison of PM ${}_{\text{EX}}$ and PM ${}_{\text{FLEX}}$ values between trials. PM ${}_{\text{EX}}$ Peak moment extension; PM ${}_{\text{FLX}}$ Peak moment flexion; *significant differences between trials in $p<$ 0.05; **significant differences between trials in $p<$ 0.01; a; significant differences from Baseline, b; significant differences from KT.

2.2 Experimental design

The study was designed as a randomised, double-blind and cross-controlled experiment. The participants visited the laboratory four times comprising one familiarisation session followed by three repeated testing sessions for all subjects. In the first session, the participants were informed about the test protocols and their height, weight and body mass index were measured. After first session, they were randomly assigned to either baseline, ‘KB’ or ‘KT’.

2.3 Isokinetic knee strength measurement

A Cybex Humac Norm, USA isokinetic dynamometer was used for testing in the seated position. Dominant limb of the subjects was fixed to an isokinetic seat with belt. Isokinetic tests were performed at three different velocities (60, 180 and 240 ${}^{\circ}$ /s) with 15 repetitions in each test condition and a rest interval of 45-s between each velocity [23]. Warm-up was performed with 10 repetitions at 300 ${}^{\circ}$ /s on an isokinetic dynamometer before the measurements Each subject was informed about basic push/pull and the number of remaining repetitions. Moreover, loud verbal encouragement was continuously given to help the participants attain the highest level of their PM values during the tests.

2.4 Kinesio taping

Kinesio Tex Gold tape, 5-cm wide (Albuquerque, NM, USA), was used in the study and applied with an I-shaped pattern on a clean and dry skin. The KT was applied in a standardised manner (origin to insertion) running from a point 10 cm below the anterior superior iliac spine to superior pole of the patella on RF muscle with 25% tension [9] to ease the RF muscle activation. For consistency of tension the KT was applied by the same investigator to all subjects.

2.5 Knee brace

DonJoy Tru-pull Advance System (11-1289/90-X- 06000) was used for this study. This brace features an elastomeric pull device with pull straps above and below the patella. It has a rubber band effect that provides a strong dynamic pull on the patella as the knee extends. The brace was worn on the dominant leg during the test [3].

2.6 Data analysis

Data were analysed using the SPSS and expressed as the mean and standard deviation. The Shapiro–Wilk test was used for assessing normality of data. Repeated measures one-way analysis of variance and LSD correction were used for analysing differences between the trials. Partial ETA was used to calculate effect size (ETA) between the trials. According to ETA ( $\eta$ ), value of $<$ 0.2 was defined as weak effect size, value of 0.5 was defined as moderate, and value of $>$ 0.8 was defined as strong effect size. Significance was defined as $p\leqslant$ 0.05.

Figure 2.

Comparison of HQR values between trials. *significant differences between trials in $p<$ 0.05; **significant differences between trials in $p<$ 0.01; a; significant differences from Baseline, b; significant differences from KT.

3. Results

For tests at 60 ${}^{\circ}$ /s, significant differences were found for PM ${}_{\text{EX}}$ ( $p=$ 0.001, $\eta=$ 0.551), PM ${}_{\text{FLX}}$ ( $p=$ 0.001, $\eta=$ 0.552) (Fig. 1), HQR ( $p=$ 0.001, $\eta=$ 0.530) between baseline, KT and KB (Fig. 2). According to these results, KT and KB developed isokinetic knee strength in both EX and FLX phases. However, at 60 ${}^{\circ}$ /s, KB was associated with a higher increase in strength compared to KT. In terms of HQRs, KB and KT increased the ratios; however, these ratios were particularly high in KB. There were no significant differences when comparing certain isokinetic strength values between Baseline, KT and KB at 180 ${}^{\circ}$ /s ( $p>$ 0.05). At 240 ${}^{\circ}$ /s, significant differences were reported in PM ${}_{\text{EX}}$ ( $p=$ 0.044, $\eta=$ 0.293), PM ${}_{\text{FLX}}$ ( $p=$ 0.001, $\eta=$ 0.555), HQR ( $p=$ 0.048, $\eta=$ 0.271) (Figs 1 and 2). In addition, the effect sizes at 60 and 240 ${}^{\circ}$ /s were moderate level with respect to PM ${}_{\text{EX}}$ , PM ${}_{\text{FLX}}$ , and the HQR.

Figure 3.

Comparison of JAPM ${}_{\text{EX}}$ , and JAPM ${}_{\text{FLEX}}$ , values between trials. JAPM ${}_{\text{EX}}$ Joint angle at peak moment in extension; JAPM ${}_{\text{FLX}}$ Joint angle at peak moment in flexion; *significant differences between trials in $p<$ 0.05; **significant differences between trials in $p<$ 0.01; a; significant differences from Baseline, b; significant differences from KT.

For JAPM ${}_{\text{EX}}$ . significant differences were found only at 60 ${}^{\circ}$ /s ( $p=$ 0.001, $\eta=$ 0.553) between baseline, KT and KB. The effect size was moderate at this speed. No significant differences were found at either speed for JAPM ${}_{\text{FLX}}$ or JAPM ${}_{\text{EX}}$ between baseline, KT and KB ( $p>$ 0.05) (Fig. 3). The application of the KB delayed the JAPM in extension while KT produced an opposite effect.

4. Discussion

This main finding of this study is that for both 60 and 240 ${}^{\circ}$ /s, KT and KB applications increased PM ${}_{\text{EX}}$ , PM ${}_{\text{FLX}}$ and HQR. Moreover, KB decreased JAPM ${}_{\text{EX}}$ , while KT increased JAPM ${}_{\text{EX}}$ . No major finding was observed at 180 ${}^{\circ}$ /s.

Previous studies reported that KT had no acute effect on muscle strength in different contractions and velocities [1, 8, 22, 23, 24, 25, 26]. Similarly, researchers have reported that KT applied to muscle groups in different joints did not have an acute effect on isokinetic strength [13, 27, 28]. However, others have shown that acute KT application improved isokinetic muscle strength and activation [6, 8, 10, 24]. Researchers have also stated that, in addition to effects of the training (especially in athletes), the increase in PM caused by KT application to the quadriceps could affect neural activation and regeneration of muscle fibres [29, 30]. In summary, there is a diversity of findings relating to the acute strength effects of KT and KB which could be attributed to the differences in training history, injury history and cutaneous afferent applications of subject groups in which KT and KB were applied. It brings to mind the idea that muscle groups, which are already developed especially in athletes, will not be significantly affected compared to the situation in sedentary individuals and individuals with a history of injury.

Studies investigating the effects of KB on isokinetic knee strength are limited. Aktaş and Baltaci [3] reported that KT and KB application increased isokinetic knee strength at 60 ${}^{\circ}$ /s and 180 ${}^{\circ}$ /s; however, the increase in strength was significant in KT application but not in KB. Lysholm et al. [31] studied females with patellofemoral pain syndrome and found greater effect of KT than KB. In another study, knee strength effects on performance could predict prophylactic KB application concluding that wearing a protective KB did not improve performance [32]. Aktaş and Baltaci [3] recommended the application of KB on knee function, but this should be stopped if it negatively affected athletic performance. The effects of KB on isokinetic strength have been studied in individuals with knee injuries and in athletic population but for the current participants wearing KB proved to be of little or no difficulty. Moreover, the results suggest that using KB will not cause any problems as long as it does not noticeably interfere with performance in athletes. Thus the choice of intervention, KB or KT, largely depends on compliance and comfort.

In this study, the increase in knee isokinetic strength in both EX and FLX phases of KT measurements is considered to be due to the ‘I’ shape technique, which is specifically aimed at increasing muscle strength in the EX phase. This result can be supported by the following theories of researchers. KT may affect the functions of muscle and myofasia by increasing blood circulation in the region where it is taped [33]. According to Ridding et al. [34], activity in both the central and peripheral nervous system may be augmented by cutaneous afferent applications, increasing motor unit stimuli and motor activation by the intense stimulation of the motor cortex. Moreover, it was suggested that motor units were stimulated more quickly and easily by reducing neuron threshold with cutaneous applications and that the increase in muscle activations increased tension in the muscle applied with KT and the muscle reflex and activation [35, 36]. Unlike the results of this study and other theories, some researchers have reported that cutaneous application of KT could increase motor activations by changing motor neuron stimuli; however, the stimuli were not strong enough to affect strength [8].

As for the asymmetry issue, asymmetric strength for the lower limb can be defined as inability of the right and left Q and H muscles to produce equal amounts of similar contraction types and may thus expose the knee [37, 38]. In this study, KT and KB applications increased HQRs and this increase was significant at 60 ${}^{\circ}$ /s and 240 ${}^{\circ}$ /s. As is known, high H/Q ratio represents a relative weakness of Q muscle or enhanced relative H strength. In healthy elite athletes, these ratios are probably at a normal level. In the studies investigating the effect of KT on knee EX and FLX strengths, it was observed that the application did not have negative effects on the ratio asymmetry [39, 40, 41]. In this study, the KB increased the HQR at 60 ${}^{\circ}$ /s and 240 ${}^{\circ}$ /s. KT, but KT did not. When the effects of KB on strength were examined, it was observed that this intervention increased exclusively the extension strength. At this point in time we can offer no explanation for the absence of a parallel effect at the medium velocity.

Our results support the idea that KT stimulates cutaneous mechanoreceptors in the taped region and that this stimulation may affect the range of motion in the lower extremity [34, 42, 43, 44]. It is suggested that in the higher angular velocities, the application of KT meant reaching the JAPM in lower angles (compared to KB) due to a possible inhibitory effect on the cutaneous mechanoreceptors.

In terms of limitations of this study, the most important is the bilateral application of KT on the RF only. Another limitation concerns the fact that we tested isokinetically in the concentric fashion only, which reveals only part of the full effect on the muscular performance.

5. Conclusion

In view of the foregoing findings and analysis we suggest that both interventions may be beneficial. Investigating further the effects of different KT taping techniques and different KB types on isokinetic variables and ultimately on the athletic performance is thus warranted.

Author contributions

CONCEPTION: Mustafa Özdal and Mehmet Vural.

PERFORMANCE OF WORK: Mustafa Özdal and Mehmet Vural.

INTERPRETATION OR ANALYSIS OF DATA: Mustafa Özdal and Mehmet Vural.

PREPARATION OF THE MANUSCRIPT: Ali Kerim Yılmaz and Menderes Kabadayı.

REVISION FOR IMPORTANT INTELLECTUAL CONTENT: Ali Kerim Yılmaz and Menderes Kabadayı.

SUPERVISION: Ali Kerim Yılmaz and Mustafa Özdal.

Ethical considerations

The study was approved by the Clinical Research Ethics Committee of Gaziantep University (2019/392).

Funding

The authors report no funding.

Footnotes

Acknowledgments

We would like to thank all of the subjects who volunteered their time to participate in the study.

Conflict of interest

The authors have no conflict of interest to report.

References

Almeida Lins

Neto

de Amorim

ABC

de Brito Macedo

Brasileiro

. Kinesio Taping® does not alter neuromuscular performance of femoral quadriceps or lower limb function in healthy subjects: Randomized, blind, controlled, clinical trial. Manual Therapy. 2013; 18(1): 41-45.

Parkkari

Kujala

Kannus

. Is it possible to prevent sports injuries? Review of controlled clinical trials and recommendations for futurework. SportsMed. 2001; 31: 984-995.

Aktas

Baltacı

. Does kinesiotaping increase knee muscles strength and functional performance. Isokinetics and Exercise Science. 2011; 19(3): 149-155.

Lehance

Binet

Bury

Croisier

. Muscular strength, functional performances and injury risk in professional and junior elite soccer players. Scandinavian Journal of Medicine & Science in Sports. 2009; 19(2): 243-251.

Masuda

Kikuhara

Demura

Katsuta

Yamanaka

. Relationship between muscle strength in various isokinetic movements and kick performance among soccer players. Journal of Sports Medicine and Physical Fitness. 2005; 45(1): 44.

Doğan

Yilmaz

Özdal

Mayda

Yilmaz

Ermiş

. Acute effects of reverse Kinesio Taping on knee muscle strength, fatigue index and H/Q ratio in healthy subjects. Isokinetics and Exercise Science. 2019; 27(2): 135-141.

Ozmen

Aydogmus

Dogan

Acar

Zoroglu

Willems

. The effect of kinesio taping on muscle pain, sprint performance, and flexibility in recovery from squat exercise in young adult women. Journal of Sport Rehabilitation. 2016; 25(1): 7-12.

Wong

Cheung,

. Isokinetic knee function in healthy subjects with and without Kinesio taping. Physical Therapy in Sport. 2012; 13(4): 255-258.

Kase

Wallis

Kase

. Clinical therapeutic applications of the kinesio taping method. Ken Ikai Co Ltd, Tokyo, 2003.

10.

Ebersole

O’Connor

Wier

. Mechanomyographic and electromyographic responses to repeated concentric muscle actions of the quadriceps femoris. J Electromyogr Kinesiol. 2006; 16(2): 149-157.

11.

Nakajima

Baldridge

. The effect of Kinesio® tape on vertical jump and dynamic postural control. Int J Sports Phys Ther. 2013; 8(4): 393.

12.

Williams

Whatman

Hume

Sheerin

. Kinesio taping in treatment and prevention of sports injuries. Sports Med. 2012; 42(2): 153-164.

13.

Zhang

Pan

Wang

Xia

Liu

. Acute effects of kinesio taping on muscle strength and fatigue in the forearm of tennis players. J Sci Med Sport. 2016; 19(6): 459-464.

14.

Thelen

Dauber

Stoneman

. The clinical efficacy of kinesio tape for shoulder pain: a randomized, doubleblinded, clinical trial. J Orthop Sports Phys Ther. 2008; 38(7): 389-395.

15.

Albright

Saterback

Stokes

. Use of knee braces in sport: current recommendations, Sports Med. 1995; 20: 281-312.

16.

Osternig

Robertson

. Effects of prophylactic knee bracing on lower extremity position and muscle activation during running. Am J Sports Med. 1993; 21: 733-737.

17.

Gulling

Lephart

Stone

Irrgang

JJ.

Pincivero

. The effect of patellar bracing on quadriceps EMG activity during isokinetic exercise. Isokin Exerc Sci. 1996; 6: 133-138.

18.

Deppen

, Landfried, Efficacy of prophylactic knee bracing in high school football players. J Orthop Sports Phys Ther. 1994; 20(5): 243-246.

19.

Teitz

Hermanson

Kronmal

. Evaluation of the use of braces to prevent injury to the knee in collegiate football players. J Bone Joint Surg. 1987; 69A: 2-9.

20.

Anandkumar

Sudarshan

Nagpal

. Efficacy of kinesio taping on isokinetic quadriceps torque in knee osteoarthritis: a double blinded randomized controlled study. Physiother Theory Pract. 2014; 30(6): 375-383.

21.

Janwantanakul

Gaogasigam

. Vastus lateralis vastus medialis obliquus muscle activity during the application of inhibition and facilitation taping techniques. Clin Rehabil. 2005; 19(1): 12-19.

22.

Osorio

Vairo

Rozea

Bosha

Millard

Aukerman

Sebastianelli

. The effects of two therapeutic patellofemoral taping techniques on strength, endurance, and pain responses. Phys Ther Sport. 2013; 14(4): 199-206.

23.

Perrin

. Isokinetic exercise and assessment. Human Kinetics, 1993.

24.

Serra

Vieira

Brunt

Goethel

Gonçalves

Quemelo

. Kinesio Taping effects on knee extension force among soccer players. Braz J Phys Ther. 2015; 19(2): 152-158.

25.

Yeung

Sakunkaruna

Mingsoongnern

Hung

Fan

Iao

. Acute effects of kinesio taping on knee extensor peak moment and electromyographic activity after exhaustive isometric knee extension in healthy young adults. Clin J Sport Med. 2015; 25(3): 284-290.

26.

Herrington

. The effect of patella taping on quadriceps strength and functional performance in normal subjects. Physical Therapy in Sport. 2004; 5(1): 33-36.

27.

Chang

Chou

Lin

Wang

. Immediate effect of forearm Kinesio taping on maximal grip strength and force sense in healthy collegiate athletes. Phys Ther Sport. 2010; 11(4): 122-127.

28.

Poon

Roper

Wong

MKM

Wong

Cheung

RTH

. Kinesiology tape does not facilitate muscle performance: A deceptive controlled trial. Manual Ther. 2015; 20(1): 130-133.

29.

Jones

Rutherford

Parker

. Physiological changes in skeletal muscle as a result of strength training. Q J Exp Physiol. 1989; 74(3): 233-256.

30.

Huang

Hsieh

. Effect of the Kinesio tape to muscle activity and vertical jump performance in healthy inactive people. BioMed Eng OnLine. 2011; 10(1): 70.

31.

Lysholm

Nardin

Ekstrand

. et al. The effect of patella brace on performance in a knee extension strength test in patient with patellar pain. Am J Sports Med. 1984; 12: 110-112.

32.

Sforzo

Chen

Gold

Frye

. The effect of prophylactic knee bracing on performance. Med Sci Sport Exerc. 1989; 21: 254-257.

33.

Kase

Stockheimer

. Kinesio Taping for Lymphadema and Chronic Swelling Albuquerque, NM: Kinesio Taping Association, 2007.

34.

Ridding

Brouwer

Miles

Pitcher

Thompson

. Changes in muscle responses to stimulation of the motor cortex induced by peripheral nerve stimulation in human subjects. Exp Brain Res. 2000; 131(1): 135-143.

35.

Kandel

Schwartz

Jessell

. Principles of neural science. 4th ed. New York: McGraw-Hill, 1991.

36.

Hsu

Chen

Lin

Wang

Shih

. The effects of taping on scapular kinematics and muscle performance in baseball players with shoulder impingement syndrome. J Electromyogr Kinesiol. 2009; 19(6): 1092-1099.

37.

Maly

Mala

Zahalka

Hank

Simkova

. Muscular strength of knee extensors and flexors and bilateral and ipsilateral ratio in elite male kickboxers. Arch Budo. 2017; 13: 107-116.

38.

Andrade

De Lira

Koffes

Mascarin

Benedito-Silva

Da Silva

. Isokinetic hamstrings-to-quadriceps peak torque ratio: the influence of sport modality, gender, and angular velocity. J Sports Sci. 2012; 30: 547-553.

39.

Chen

Hong

Huang

Hsu

. Effects of kinesio taping on the timing and ratio of vastus medialis obliquus and vastus lateralis muscle for person with patellofemoral pain. J Biomech. 2007; 40: 318.

40.

De Hoyo

Álvarez-Mesa

Sañudo

Carrasco

Domínguez

. Immediate effect of kinesio taping on muscle response in young elite soccer players. J Sport Rehabil. 2013; 22(1): 53-58.

41.

García-Muro

Rodríguez-Fernández

ÁL

Herrero-de-Lucas

. Treatment of myofascial pain in the shoulder with Kinesio taping. A case report. Manual Ther. 2010; 15(3): 292-295.

42.

Halseth

McChesney

DeBeliso

Vaughn

Lien

, The effects of Kinesio taping on proprioception at the ankle, J Sport Sci Med. 2004; 3: 1-7.

43.

Murray

Husk

. Effect of kinesio taping on proprioception in the ankle, J Orthop Sports Phys Ther. 2001; 31: A-37.

44.

Johnson

Palmieri-Smith

Lepley

. Contribution of Neuromuscular Factors to Quadriceps Asymmetry After Anterior Cruciate Ligament Reconstruction. Journal of Athletic Training. 2018; 53: 347-354.

A comparative study of the acute effects of knee brace vs. kinesiotape on selected isokinetic strength variables of the knee muscles

Abstract

BACKGROUND:

OBJECTIVE

METHODS:

RESULTS:

CONCLUSION:

Keywords

1. Introduction

2. Methods

2.1 Participants

Table 1 Descriptive parameters of subjects

2.3 Isokinetic knee strength measurement

2.4 Kinesio taping

2.5 Knee brace

2.6 Data analysis

5. Conclusion

Author contributions

Ethical considerations

Funding

Footnotes

Acknowledgments

Conflict of interest

References

Table 1
Descriptive parameters of subjects