Effects of high intensity interval training on plasma

levels of growth hormone and insulin like growth

factor-1 in healthy males

Seyyed Mahmoud Hejazi

Department of Physical Education, Mashhad Branch, Islamic Azad University, Mashhad, Iran

ABSTRACT

It is well-recognized that exercise has a signi cant impact on the growth hormone / insulin-like growth factor GH/

IGF system but less is known about the effects of high intensity training (HIT) on this axis. Aim of the present study

was to evaluate the effect of ten weeks of HIT on plasma levels of GH and IGF-I in healthy men. Twenty young men

(age 23.34±2.56 weight 72.47±12.01 height 174.10 ± 5.75) recruited and randomly assigned into Control (n=10) and

HIT (n=12) groups. HIT protocol was started with 4 cycles. Then, every two weeks one cycle was added to the previ-

ous ones. Finally it was to 8 cycles/session in tenth weeks that lasted 16 minutes. Blood samples were collected prior

to and after HIT program for all subjects and IGF-I and GH levels were measured. HIT subjects showed a signiﬁcant

increase in IGF-I (P=0.002, F=12.38). However no signi cant change was shown in GH levels (P=0.716, F=0.62).Our

ﬁndings indicate that the HIT caused increase in circulating levels of IGF-I independently from GH levels. Both hor-

mones may contribute to positive effects of anabolic conditions.

KEY WORDS: IGF-I/GH AXIS, HIT, ADAPTATION

199

ARTICLE INFORMATION:

*Corresponding Author: Sm.hejazi37@gmail.com

Received 27

Dec, 2016

Accepted after revision 2

March, 2017

BBRC Print ISSN: 0974-6455

Online ISSN: 2321-4007

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Online Contents Available at: http//www.bbrc.in/

Biosci. Biotech. Res. Comm. Special Issue No 1:199-202 (2017)

INTRODUCTION

Growth hormone (GH) is the principal regulator of the

hepatic synthesis of insulin-like growth factor I (IGF-

1). IGF-1 itself is the primary downstream mediator of

GH actions, and circulating IGF-1 plays an important

role in the feedback regulation of GH secretion. However

IGF-1, produced in skeletal muscle during exercise, is

also released into the circulation which might explain

an increase in Circulating IGF-1 levels as well Frystyk

(2010) and Nindl (2010). IGF-1 has widespread anabolic

and insulin-sensitizing effects, and plays a critical role

in formation, maintenance, and regeneration of skeletal

muscles. IGF-1 also plays a direct role in whole body

glucose homeostasis primarily by stimulating skeletal

muscle glucose uptake (Berg and Bang 2004).

200 EFFECTS OF HIGH INTENSITY INTERVAL TRAINING ON PLASMA LEVELS OF GROWTH HORMONE BIOSCIENCE BIOTECHNOLOGY RESEARCH COMMUNICATIONS

Seyyed Mahmoud Hejazi

Nindl et al. (2010) stated that IGF-1 is an important

metabolic biomarker associated with a variety of health

and exercise-related outcomes. It is well-recognized that

exercise has a signi cant impact on the GH/IGF sys-

tem, number of factors have led to interest in the effect

of exercise on the growth hormone/insulin-like growth

factor-I (GH/IGF-I) axis, including its possible role in

maintenance of lean mass in a variety of physiological

actions like protein synthesis, cellular proliferation and

glucose metabolism, (Brill et al., 2002 and Weltman et

al 2003).

Although most modes of exercise stimulate an

increased GH secretory response that is linear with

exercise intensity evidence suggests IGF-I responses are

independent of GH. Insulin-like growth factor I (IGF-1)

is a polypeptide of 70 amino acids (7650 daltons), and

is one of a number of related insulin-like growth factors

present in the circulation.The molecule has a number of

biological activities similar to insulin. IGF-1 concentra-

tions change with age, nutritional status, body composi-

tion and physical activity, m(Roy et al 1985, Hornum et

al 1985, Stitt et al.2004).Whether previous studies have

reported exercise-induced alterations of IGF-I seems to

depend on several factors, including exercise model.

Both low- and high-intensity cycling have been shown

to increase IGF-I concentrations. However, neither low-

volume nor high-volume resistance exercise has been

shown to change total IGF-I concentrations, (Cappon et

al., 1994 and Nindl et al., 2001).

Moreover, no change in IGF-I concentrations has

been found following a marathon, a 20 km run, and

treadmill exercise at 60% of Vo max. The ability of IGF-I

to promote muscle hypertrophy is unchallenged; how-

ever, several lines of evidence have demonstrated that

load-induced hypertrophy can occur independently of

IGF-I and/or activation of the IGF-I receptor. Conversely,

evidence in support of IGF-I as a “regulator or ampliﬁer”

of muscle remodeling cascades also exists, (Hagberg et

al., 1988, Ban et al., 1994, Spangenburg et al., 2008

and Flueck and Goldspink 2011).

HIT exercises are high intensity and interval that can

be done in a short time, although has the bene ts of

long-term endurance exercise. Even though the recent

studies have shown endurance training can induce an

increase of GH, IGF-1, levels in the circulation, but less

is known about the effects of different training inten-

sities (e. g. high-intensity training (HIT) on circulating

levels of these growth factors. Only a few studies have

addressed this issue in a strictly experimental way. The

purpose of the present study was to evaluate the effect

of ten weeks of HIT on plasma levels of GH and IGF-I

in healthy men. The present study differs from previ-

ous studies, the protocol was more rigorous and exercise

responses were compared with a non-exercise control

trial, (Schwarz et al 1996 and Laursens and Jenkins

2002).

METHODS

STUDY DESIGN /PARTICIPANTS

Trial design was semi-experimental with control

group. Twenty two young men (age 23.34±2.56 weight

72.47±12.01 height 174.10 ± 5.75) recruited via a recall

in Ferdowsi university of Mashhad campuses and those

approved participation were randomized into either a

training group (HIT) or a control group (CON). Informed

consentwas obtained from each patient included in the

study and the study protocol conforms to the ethical

guidelinesof the1975 Declaration of Helsinki.Exclusion

criteria include professional athletics history as well as

the current regular exercise, smoking, cardiovascular

and metabolic disease or any complication that disrupt

the implementation of exercise.

HIT group after became acquainted with the correct

training performances, carried out the exercises, every

other day, three sessions a week, for 10 weeks. Exer-

cises included warm up, HIT training, cool down. Sub-

jects warmed up by stretching and easy walking for 5

minutes. The HIT interventions consisted of four 30 s

maximal effort (“all-out”) shuttle run bouts (from cone-1

to cone-2 ,20 meter sweep) separated by 1.5 min passive

rest each (Fig. 1).

HIT protocol began with 4 cycles and every two weeks

added one cycle. Finally it was 8 cycles in tenth week

that lasted 16 minutes. Cooling Down also included 5

BIOSCIENCE BIOTECHNOLOGY RESEARCH COMMUNICATIONS EFFECTS OF HIGH INTENSITY INTERVAL TRAINING ON PLASMA LEVELS OF GROWTH HORMONE 201

Seyyed Mahmoud Hejazi

Table 1. Study variables before (pre) and after (post) 10 weeks of study protocol

Variable Control HIT ANOVA

(Repeated

Measurement)

Pre test Post test Pre test Post test

IGF-I (ng /mL) 193.10± 33.54 190.60 ± 32.32 199.27 ± 28.69 222.27 ± 32.90 F=12.38

P=0.002

GH (ng /mL ) 3.053±0.73 3.004±0.53 3.241±0.41 3.158±0.61 F=0.62

P=0.716

Data are mean ± SD

min of walking and stretching. During the HIT interven-

tions all subjects were vocally encouraged to maintain

Maximal effort. Quality of training was controlled by a

physical education expert and subject’s heartbeat was

constantly checked by polar device. Control group asked

to be sedentary in this period.

Twenty four hours before starting the exercise pro-

gram, while all the subjects were fasten; 5 cc of blood

was taken from their brachial vein. Also sampling

repeated after 48 hours of last session in same condition.

Blood samples were frozen in -20 for future analysis.

LDN (Germany) ELISA assay Kit was used to measure

IGF-I concentrations which Sensitivity was 1.292 ng /

mL and monobind (USA) ELISA assay Kit was used to

measure GH concentrations which Sensitivity was 0.072

ng /mL.

Data normality was tested using Shapiro-wilk and the

homogeneity of the variances was tested using levene.

After making sure of the normality and equality of the

groups, variance analysis with repeated measuring was

used to study the differences between groups. Statistical

analysis was done by the SPSS Software.

RESULTS AND DISCUSSION

After ten weeks HIT subjects showed a signiﬁcant

increase in IGF-I (P=0.002, F=12.38). However no signif-

icant change was shown in GH levels (P=0.716, F=0.62).

(Table 1).

Previous studies have been reported that exercise has

a signi cant impact on the levels of several hormones,

and can increase resistance and performance, as well

as muscle mass. Hormone levels can change according

to several parameters, including the type and length of

exercise, the duration of time following exercise, the

age and gender of the athletes, among others, Kraemer

et al (2006). Based on the  ndings from the present

research, plasma levels of IGF-I had been signi cantly

increased due to HIT protocol. To our knowledge, no

previous research has directly investigated the impacts

of HIT on IGF-I/GH axis. However, other types of train-

ing have been published. Most of the training time dur-

ing the HIT intervention was spent in recovery between

short, intense bursts of all-out shuttle running. This is

in accordance with previously published studies, (Wahl

et al 2010).

Several studies have indicated that anabolic hor-

mones, such as insulin, GH, testosterone and IGF-1,

stimulate neural tissue and muscle development dur-

ing resistance exercise, (Crewther et al 2006). The serum

concentration of anabolic hormones is elevated during

and following resistance exercise compared to the level

at rest, which leads to hypertrophy and remodeling of

muscle ( Widdowson et al., 2009). Circadian rhythm

has speci c effects on the release of IGF-1 in the body,

where the hormone levels are higher in the morning and

lower in the afternoon, (Hayes et al., 2010).

In the present study GH concentrations did not sig-

ni cantly changed as a result of relative long term HIT.

That regard should be considered that due to our study

limitation, GH only measured at one point in time. Also

regarding Circadian rhythm and the pulsatile man-

ner of GH it will probably cause different results when

compared with multi-time point, whereas long-term

exercise training approximately doubles integrated GH

concentrations when measured on non-exercising days.

Linnamo et al. reports that GH levels are increased in

response to submaximal and maximal heavy resistance

exercise. However, the prominent increase was detected

just after the exercise session was completed, and the

response returned to normal level two hours post exer-

cise, (Weltman et al., 1992 and Linnamo et al., 2005).

Different training intensities, such as high-intensity

training and high volume, low-intensity training may

have a different impact on hormone levels. Although pH

is generally well regulated, a more increase in the acidity

of the circulating blood and the skeletal muscle occurs

when performing HIT. One can speculate that these sys-

temic and local changes in the extracellular environment

might in uence the release, the af nity, and association/

dissociation of GH, IGF-1. The extracellular pH has been

recognized to regulate the IGF-1 interactions with dif-

ferent cells, components of the extracellular, (Gordon

et al 1994 and Gibala et al 2006).

Seyyed Mahmoud Hejazi

202 EFFECTS OF HIGH INTENSITY INTERVAL TRAINING ON PLASMA LEVELS OF GROWTH HORMONE BIOSCIENCE BIOTECHNOLOGY RESEARCH COMMUNICATIONS

In summary, we undertook a randomized trial of the

impact of 10 weeks of HIT on IGF-I/GH axis in previ-

ously untrained subjects. The major  nding was HIT

caused increase in circulating levels of IGF-I indepen-

dently from GH levels. Both hormones may contribute to

the positive effects of anabolic conditions as it has been

shown by previous studies.

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