It's a disturbing thought, one that usually hits after an unexpected physical challenge. Maybe you've been unable to maintain your usual workout levels, or recovery is taking a lot longer than it used to. Perhaps fixes to the house are just a bit more difficult, or you find yourself feeling tired more often.

What's most startling about this realization is that you don't normally "feel old" but, nevertheless, you know you're not the man you used to be.

And the issue? It could be a decrease in your testosterone.

Most people don't realize that testosterone is a vital hormone for maintaining overall good health. An article from Livestrong.com noted that when testosterone levels start to decline, men experience a gradual reduction in muscle density, size and strength. Testosterone stimulates the use of stored body fat for energy and keeps you looking lean, but when your levels decrease fatigue can set in from the breakdown of muscle tissue and poor energy production.

"You also see an increased incidence of cardiovascular disease, diabetes, osteoporosis and other age-related illness that occur as testosterone levels slowly decline with age," the article adds. "Lower testosterone levels are associated with increased obesity, diabetes, fatigue, lower cognitive abilities, depression and heart disease."

Testosterone replacement therapy is one possible way of handling the situation, but it must be done through a doctor and research is mixed on whether or not it actually works. The real trick is getting the body to safely start producing more testosterone on its own, and one of the most exciting approaches has been the recent development of a safe and effective supplement which actually triggers the body to raise free testosterone levels naturally.

It’s called Natural-T and it’s now available to the public. Natural-T relies on well-researched natural testosterone boosting ingredients such as Fenugreek, Tribulus Alatus, Basella Alba, Brassinosteroids, Safed Musli, White Button Mushroom, Ursolic Acid, Bioperine®, and Astravar™ which can significantly pump up a person’s free testosterone levels.

The product has no harmful side effects and has been shown to deliver improvements in strength and endurance in just days. In fact, the company states that results of Natural-T include enhanced physical performance and stamina.

What kind of a difference can a testosterone boosting supplement like this make?

According to users of the product, it’s nothing short of spectacular. From increased muscle definition and quicker recovery times, to increased feelings of alertness and greater endurance, these users are reporting virtual transformations as a result of safely boosting their free testosterone with Natural-T.

Natural-T is manufactured under the strictest quality standards and is available at GNC online and at select stores across the nation.

Best of all, right now, the company that manufacturers Natural-T is giving away samples of the products to qualifying customers who request them online.

The teenage bombing suspect who was captured Friday night hiding in a boat in the Watertown neighborhood near Boston reportedly attended a party at two nights after the incident, The Boston Globe reported.

"He was just relaxed," said a student from Umass Dartmouth who saw the suspect, Dzhokhar Tsarnaev, mingling with friends from intramural soccer.

Tsarnaev is registered at the school and the campus sent out an alert on its website Friday saying, "The campus is closed. Individuals on campus should shelter in place unless instructed otherwise."

Several students were interviewed in the report and expressed disbelief that their fellow classmate was a suspect in the Boston Marathon bombing that killed three and injured over 180 people.

Pamala Rolon, 22, a senior at the school, told the paper that when images of the suspect first appeared in the media, students made jokes that the person looked similar to Tsarnaev but ‘then we thought it just couldn’t be him. Dzhokhar? Never.’

Sonia Ribeiro, 19, of Boston, was in a philosophy class with Tsarnaev. She also said he was on campus this week, although not in class.

"He was laid back. I would never expect this at all from him," she said.

Law enforcement officials and family members identified the suspects as Dzhokhar Tsarnaev and his older brother Tamerlan.

They were ethnic Chechen brothers who had lived in Dagestan, which neighbors Chechnya in southern Russia. Tamerlan was killed in a shootout with police while Dzhokhar escaped.

Florida Addy, 19, of Lynn, lived on the same dormitory floor as Dzhokhar Tsarnaev last year. She called him "drug" — the Russian word for friend, pronounced "droog" — and said they would sometimes hang out together in his room.

She said she hung out with him and some other Russian students at an apartment in New Bedford, not far from campus. She said they would always speak Russian among themselves.

Amber Rose took to her Twitter this week to show off the latest addition in her tattoo collection: a large portrait of her fiance and baby daddy, Wiz Khalifa.

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Tattooist Bobby Serna confirmed that this indeed was not a joke on his Instagram, writing, "Khalifa Man @mistercap , Tattoed on my Homegirl @muvarosebud , thanks y'all for the opportunity and congrats to the both of you!#CamAndAmb#youngwildNFree#TGOD."

However, the "Black and Yellow" rapper isn't the only person whose face occupies a part of Rose's body.

The model -- who's been engaged to Khalifa since March 2012 and welcomed son Sebastian Taylor Thomaz just almost two months ago -- also had a portrait of her mother done by the same artist.

Production on the David O. Russell drama "American Hustle" has been stopped for the time being, this according to Deadline.com. The film -- which is based on the ABSCAM sting operation on the East Coast that happened during the late 1970s and early 1980s -- stars Bradley Cooper, Jennifer Lawrence, Christian Bale, Amy Adams and Jeremy Renner.

Sony, the studio behind "American Hustle," is releasing Russell's latest in the fourth quarter of 2013; it's expected to be another Oscar contender for the director, following in the footsteps of "The Fighter" and "Silver Linings Playbook."

"American Hustle" was filming in Worcester, Mass. on Monday when bombs went off at the finish line of the Boston Marathon, killing three and injuring more than 170. The city is located 46 miles west of Boston. According to EW.com, production on "American Hustle" returned to the Boston city limits on Wednesday. With a manhunt underway, however, for Dzhokhar Tsarnaev (the 19-year-old bombing suspect who evaded police after a shootout early on Friday morning), "American Hustle" filming has been put on hold for now.

Earlier on Friday, a photo of "American Hustle" star Cooper and New England Patriots wide receiver Julian Edelman visiting bombing victim Jeff Bauman circulated on social media and news sites (including The Huffington Post). Bauman helped authorities identify Tsarnaev and his brother, Tamerlan, who died earlier on Friday during the same police shootout.

For more on "American Hustle," including what Sony had to say about the delay, head over to Deadline.com.