Physical Development in Early Adulthood

What you’ll learn to do: explain developmental tasks and physical changes during early adulthood

A group of women doing a forward bend in a yoga class

In this section, we will see how young adults are often at their peak physically, sexually, and in terms of health and reproduction; yet they are also particularly at risk for injury, violence, substance abuse, sexually transmitted diseases, and more. As you read, consider whether or not you think young adults are in the prime of their lives.

Learning Outcomes

  • Summarize the developmental tasks of early adulthood
  • Describe physical development and health in early adulthood
  • Summarize risky behaviors and causes of death in early adulthood
  • Describe sexuality and fertility issues related to early adulthood

Developmental Tasks of Early Adulthood

College students studying and talking on the grass.
Figure 1. How old do you think this group of young adults are? What clues can you use to help you estimate their age?

Before we dive into the specific physical changes and experiences of early adulthood, let’s consider the key developmental tasks during this time—the ages between 18 and 40. The beginning of early adulthood, ages 18-25, is sometimes considered its own phase, emerging adulthood, but the developmental tasks that are the focus during emerging adulthood persist throughout the early adulthood years. Look at the list below and try to think of someone you know between 18 and 40 who fits each of the descriptions.

Developmental Tasks of Early Adulthood

Havighurst (1972) describes some of the developmental tasks of young adults. These include:

  1. Achieving autonomy: trying to establish oneself as an independent person with a life of one’s own
  2. Establishing identity: more firmly establishing likes, dislikes, preferences, and philosophies
  3. Developing emotional stability: becoming more stable emotionally which is considered a sign of maturing
  4. Establishing a career: deciding on and pursuing a career or at least an initial career direction and pursuing an education
  5. Finding intimacy: forming first close, long-term relationships
  6. Becoming part of a group or community: young adults may, for the first time, become involved with various groups in the community. They may begin voting or volunteering to be part of civic organizations (scouts, church groups, etc.). This is especially true for those who participate in organizations as parents.
  7. Establishing a residence and learning how to manage a household: learning how to budget and keep a home maintained.
  8. Becoming a parent and rearing children: learning how to manage a household with children.
  9. Making marital or relationship adjustments and learning to parent.


Think It Over

To what extent do you think these early adulthood developmental tasks have changed in the last several years? How might these tasks vary by culture?

Physical Development in Early Adulthood

The Physiological Peak

Young man in great physical condition doing a side plank.
Figure 2. Early adulthood is generally a time of peak physical health.

People in their twenties and thirties are considered young adults. If you are in your early twenties, you are probably at the peak of your physiological development. Your body has completed its growth, though your brain is still developing (as explained in the previous module on adolescence). Physically, you are in the “prime of your life” as your reproductive system, motor ability, strength, and lung capacity are operating at their best. However, these systems will start a slow, gradual decline so that by the time you reach your mid to late 30s, you will begin to notice signs of aging. This includes a decline in your immune system, your response time, and in your ability to recover quickly from physical exertion. For example, you may have noticed that it takes you quite some time to stop panting after running to class or taking the stairs. But, remember that both nature and nurture continue to influence development. Getting out of shape is not an inevitable part of aging; it is probably due to the fact that you have become less physically active and have experienced greater stress. The good news is that there are things you can do to combat many of these changes. So keep in mind, as we continue to discuss the lifespan, that some of the changes we associate with aging can be prevented or turned around if we adopt healthier lifestyles.

In fact, research shows that the habits we establish in our twenties are related to certain health conditions in middle age, particularly the risk of heart disease. What are healthy habits that young adults can establish now that will prove beneficial in later life? Healthy habits include maintaining a lean body mass index, moderate alcohol intake, a smoke-free lifestyle, a healthy diet, and regular physical activity. When experts were asked to name one thing they would recommend young adults do to facilitate good health, their specific responses included: weighing self often, learning to cook, reducing sugar intake, developing an active lifestyle, eating vegetables, practicing portion control, establishing an exercise routine (especially a “post-party” routine, if relevant), and finding a job you love.[1]

Being overweight or obese is a real concern in early adulthood. Medical research shows that American men and women with moderate weight gain from early to middle adulthood have significantly increased risks of major chronic disease and mortality (Zheng, et al, 2017).[2] Given the fact that American men and women tend to gain about one to two pounds per year from early to middle adulthood, developing healthy nutrition and exercise habits across adulthood is important (Nichols, 2017).[3]

Watch It

This video explains how the brain continues to develop into adulthood.

A Healthy, but Risky Time

Early adulthood tends to be a time of relatively good health. For instance, in the United States, adults ages 18-44 have the lowest percentage of physician office visits than any other age group, younger or older. However, early adulthood seems to be a particularly risky time for violent deaths (rates vary by gender, race, and ethnicity). The leading causes of death for both age groups 15-24 and 25-34 in the U.S. are unintentional injury, suicide, and homicide. Cancer and heart disease follow as the fourth and fifth top causes of death among young adults (Centers for Disease Control and Prevention, 2019).

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Substance Abuse

Rates of violent death are influenced by substance abuse, which peaks during early adulthood. Some young adults use drugs and alcohol as a way of coping with stress from family, personal relationships, or concerns over being on one’s own. Others “use” because they have friends who use and in the early 20s, there is still a good deal of pressure to conform. Youth transitioning into adulthood have some of the highest rates of alcohol and substance abuse. For instance, rates of binge drinking (drinking five or more drinks on a single occasion) in 2014 were: 28.5 percent for people ages 18 to 20 and 43.3 percent for people ages 21-25.[4] Recent data from the Centers for Disease Control and Prevention show increases in drug overdose deaths between 2006 and 2016 (with higher rates among males), but with the steepest increases between 2014 and 2016 occurring among males aged 24-34 and females aged 24-34 and 35-44. Rates vary by other factors including race and geography; increased use and abuse of opioids may also play a role.

Watch It

To learn more about opioid drugs and the current opioid crisis, please watch the following video:

Drugs impair judgment, reduce inhibitions, and alter mood, all of which can lead to dangerous behavior. Reckless driving, violent altercations, and forced sexual encounters are some examples. College campuses are notorious for binge drinking, which is particularly concerning since alcohol plays a role in over half of all student sexual assaults. Alcohol is involved nearly 90 percent of the time in acquaintance rape (when the perpetrator knows the victim). Over 40 percent of sexual assaults involve alcohol use by the victim and almost 70 percent involve alcohol use by the perpetrator. [5].

Link to Learning

After she was the victim of an assault in London, college student Ione Wells published a letter to her attacker in a student newspaper that went viral and sparked the #NotGuilty campaign against sexual violence and victim-blaming. Watch Ione Wells’ TED talk “How We Talk About Sexual Assault Online” ( to learn more [Note: this is a sensitive topic.]

Drug and alcohol use increase the risk of sexually transmitted infections because people are more likely to engage in risky sexual behavior when under the influence. This includes having sex with someone who has had multiple partners, having anal sex without the use of a condom, having multiple partners, or having sex with someone whose history is unknown. Such risky sexual behavior puts individuals at increased risk for both sexually transmitted diseases (STDs) and human immunodeficiency virus (HIV). STDs are especially common among young people. There are about 20 million new cases of STDs each year in the United States and about half of those infections are in people between the ages of 15 and 24. Also, young people are the most likely to be unaware of their HIV infection, with half not knowing they have the virus (Centers for Disease Control and Prevention, 2019).

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Sex and Fertility in Early Adulthood

Sexual Responsiveness and Reproduction in Early Adulthood

Sexual Responsiveness

Men and women tend to reach their peak of sexual responsiveness at different ages. For men, sexual responsiveness tends to peak in the late teens and early twenties. Sexual arousal can easily occur in response to physical stimulation or fantasizing. Sexual responsiveness begins a slow decline in the late twenties and into the thirties although a man may continue to be sexually active throughout adulthood. Over time, a man may require more intense stimulation in order to become aroused. Women often find that they become more sexually responsive throughout their 20s and 30s and may peak in the late 30s or early 40s. This is likely due to greater self-confidence and reduced inhibitions about sexuality.

There are a wide variety of factors that influence sexual relationships during emerging adulthood; this includes beliefs about certain sexual behaviors and marriage. For example, among emerging adults in the United States, it is common for oral sex to not be considered “real sex”. In the 1950s and 1960s, about 75 percent of people between the ages of 20–24 engaged in premarital sex; today, that number is 90 percent. Unintended pregnancy and sexually transmitted infections and diseases (STIs/STDs) are a central issue. As individuals move through emerging adulthood, they are more likely to engage in monogamous sexual relationships and practice safe sex.


For many couples, early adulthood is the time for having children. However, delaying childbearing until the late 20s or early 30s has become more common in the United States. The mean age of first-time mothers in the United States increased 1.4 years, from 24.9 in 2000 to 26.3 in 2014. This shift can primarily be attributed to a larger number of first births to older women along with fewer births to mothers under age 20 (CDC, 2016).[6]

Couples delay childbearing for a number of reasons. Women are now more likely to attend college and begin careers before starting families. And both men and women are delaying marriage until they are in their late 20s and early 30s. In 2018, the average age for a first marriage in the United States was 29.8 for men and 27.8 for women.[7]


Infertility affects about 6.7 million women or 11 percent of the reproductive age population (American Society of Reproductive Medicine [ASRM], 2006-2010. Male factors create infertility in about a third of the cases. For men, the most common cause is a lack of sperm production or low sperm production.  Female factors cause infertility in another third of cases. For women, one of the most common causes of infertility is ovulation disorder. Other causes of female infertility include blocked fallopian tubes, which can occur when a woman has had pelvic inflammatory disease (PID) or endometriosis. PID is experienced by 1 out of 7 women in the United States and leads to infertility about 20 percent of the time. One of the major causes of PID is Chlamydia, the most commonly diagnosed sexually transmitted infection in young women. Another cause of pelvic inflammatory disease is gonorrhea. Both male and female factors contribute to the remainder of cases of infertility and approximately 20 percent are unexplained.

Watch It

Watch this video to learn more about the reasons for infertility and the main treatment methods available for conceiving.

Fertility Treatment

The majority of infertility cases (85-90 percent) are treated using fertility drugs to increase ovulation or with surgical procedures to repair the reproductive organs or remove scar tissue from the reproductive tract.  In vitro fertilization (IVF) is used to treat infertility in less than 5 percent of cases. IVF is used when a woman has blocked or deformed fallopian tubes or sometimes when a man has a very low sperm count. This procedure involves removing eggs from the female and fertilizing the eggs outside the woman’s body. The fertilized egg is then reinserted in the woman’s uterus. The average cost of an IVF cycle in the U.S. is $10,000-15,000 and the average live delivery rate for IVF in 2005 was 31.6 percent per retrieval.  IVF makes up about 99 percent of artificial reproductive procedures. [ASRM, 2006-2010]

Less common procedures include gamete intrafallopian tube transfer (GIFT) which involves implanting both sperm and ova into the fallopian tube and fertilization is allowed to occur naturally. Zygote intrafallopian tube transfer (ZIFT) is another procedure in which sperm and ova are fertilized outside of the woman’s body and the fertilized egg or zygote is then implanted in the fallopian tube. This allows the zygote to travel down the fallopian tube and embed in the lining of the uterus naturally. 

Insurance coverage for infertility is required in fourteen states, but the amount and type of coverage available vary greatly (ASRM, 2006-2010). The majority of couples seeking treatment for infertility pay much of the cost. Consequently, infertility treatment is much more accessible to couples with higher incomes. However, grants and funding sources may be available for lower-income couples seeking infertility treatment.

Fertility for Singles and Same-Sex Couples

The journey to parenthood may look different for singles same-sex couples.  However, there are several viable options available to them to have their own biological children. Men and women may choose to donate their sperm or eggs to help others reproduce for monetary or humanitarian reasons. Some gay couples may decide to have a surrogate pregnancy. One or both of the men would provide the sperm and choose a carrier. The chosen woman may be the source of the egg and uterus or the woman could be a third party that carries the created embryo.

Reciprocal IVF is used by couples who both possess female reproductive organs. Using in vitro fertilization, eggs are removed from one partner to be used to make embryos that the other partner will hopefully carry in a successful pregnancy.

Artificial insemination (AI) is the deliberate introduction of sperm into a female’s cervix or uterine cavity for the purpose of achieving a pregnancy through in vivo fertilization by means other than sexual intercourse. AI is most often used by single women who desire to give birth to their own child, women who are in a lesbian relationship, or women who are in a heterosexual relationship but with a male partner who is infertile or who has a physical impairment which prevents intercourse. The sperm used could be anonymous or from a known donor.

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artificial insemination: the deliberate introduction of sperm into a female’s cervix in order to become pregnant by means other than sexual intercourse
chlamydia: a sexually transmitted infection caused by the bacterium chlamydia trachomatis
endometriosis: a condition in which the layer of tissue that normally covers the inside of the uterus, grows outside of it
gamete intrafallopian tube transfer: involves implanting both sperm and ova into the fallopian tube which allows fertilization to occur naturally
gonorrhea: a sexually transmitted infection (STI) caused by the bacterium neisseria gonorrhoeae
in vitro fertilization: this procedure involves removing eggs from the female, fertilizing the eggs outside the woman’s body, and then reinserting into the woman’s uterus
pelvic inflammatory disease: an infection of the upper part of the female reproductive system, namely the uterus, fallopian tubes, and ovaries, and inside of the pelvis
zygote intrafallopian tube transfer: sperm and ova are fertilized outside of the woman’s body and the zygote is then implanted in the fallopian tube to allow the zygote to travel and embed in the lining of the uterus naturally

  1. Parker-Pope, T. (October 17, 2016). The 8 Health Habits Experts Say You Need in Your 20s. NY Times.
  2. Zheng, Y., Manson, J.E., Yuan, C., Liang, M.H., Grodstein, F., Stampfer, M.J., Willett, W.C., & Hu, F.B. (2017, July 18). Associations of weight gain from early to middle adulthood with major health outcomes later in life. JAMA, 318(3): 255-272. doi:10.1001/jama.2017.7092
  3. Nichols, H. (2017, July 18). Weight gain in early adulthood linked to health risks later in life. Medical News Today.
  4. Substance Abuse and Mental Health Services Administration (2018). SAMHSA. Retrieved from
  5. (2018). Sexual Assaults on College Campuses Involving Alcohol. Retrieved from
  6. T.J. Mathews, M.S. and Brady E. Hamilton, Ph.D. Mean Age of Mothers is on the Rise: United States, 2000–2014. NCHS Data Brief No. 232, January 2016. Retrieved from
  7. U.S Census Bureau (2018) Historical Marital Status Tables. Retrieved from


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